This is our most complete and updated guide on climate change.
Climate change can be confusing and time consuming to research, so we’ve aimed to summarise (on one page) some of the key aspects of the issue to be aware of, along with what might be some of the most important lines of information and data.
This might be a good ‘starter guide’ for those looking to better understand some of the basic foundations of the issue.
(*Note – this is just one summary of climate change. You may like to read a wide and diverse range of other content and publications from different sources to ensure you feel you are adequately informed)
Summary – Climate Change & Global Warming
At it’s core, climate change is about the warming trend of Earth’s climate since 1880 (Earth’s global average surface temperature has risen roughly 0.8 degrees celsius since this time)
[Note though that climates can change on both a regional/local level, and also on the global average level … this is it is said that some regional climates might warm, whilst others might cool]
The current scientific consensus is: with all the currently available data, lines of evidence, and studies, and taking into account what is thought to have caused a change in the climate in the past, there is a current scientific consensus that anthropogenic (coming from humans) greenhouse gas emissions (i.e. mainly CO2) from the burning fossil fuels are the primary cause/driver to Earth’s recent Earth warming trend (i.e. the last century or so)
Natural causes are thought to only impact the climate on very short time periods such as over the course of a decade (as opposed to hundreds or thousands, or even millions of years).
The warming trend is thought to be of significance in large part because of how much global average temperature is increasing in such a short amount of time (much of the warming has happened in the last few decades – two thirds of the warming has happened since 1975).
In addition, the warming has happened in unison with increased burning of fossil fuels, and the resultant increased atmospheric levels of carbon dioxide (currently at over 410 parts per million).
Going back even roughly 22,000 years ago when modern humans and civilisations were developing, and Earth was coming out of an ice age, warming was thought to be far more gradual, and happened over a much longer timespan of millennia.
Around the end of the industrial revolution, warming rates and CO2 levels seemed to have changed quickly.
Even taking into consideration the uncertainties about different aspects of the climate change issue (such as Earth’s climate and CO2 levels in the past, and future projections of climate change), the evidence and data links most strongly to CO2 from human emissions being the primary cause behind the recent rapid warming trend of the Earth’s climate (and especially in the last several decades).
In lieu of this, and since assessing the potential risk that the future potential effects of each additional degree of warming climate change may present, it is proposed that the world employs mitigation, sequestration and adaptation measures and solutions.
An example of mitigation is incrementally decreasing and bringing emissions to net zero within relevant timelines to meet warming targets below 2 degrees celsius (above pre industrial levels).
Geo-engineering is another potential response, although it’s seen as controversial by some.
Some solutions might be broad solutions, whilst other can be custom to different countries, States/provinces, cities, sectors, and individuals.
Something that is mentioned about addressing a changing climate is managing the risk.
What that means is that even if greenhouse gas emissions from human sources can’t be proved 100% to be to primary cause of the warming trend, there is still a risk that has to be managed for the possibility that these GHGs are the cause (that possibility could theoretically be 99% or lower).
If nothing is done to address it, then nothing is being done to manage that risk.
So, risk management might unofficially play a part in climate change solutions.
Either way, if the climate changes, adaptation to a changing climate is going to be required in some capacity.
Some of the other key lines of information, and important considerations, central to understanding the climate change and global warming issue (in dot point form) might be:
– From 1880, up until the present, the Earth’s global average surface temperature has risen by between 0.8 to 1 degree celsius
– In the same time period, carbon dioxide levels (measured in parts per million) in the atmosphere have risen to 411ppm as of 2019.
– In at least the last (roughly) 22,000 years since Earth came out of the last ice age, warming has not increased this rapidly in such a short period of time (mixed with some short periods of cooling, Earth has gradually and slowly warmed from about -4.3 degrees celsius since this ice age)
– Additionally, some reports indicate that the carbon dioxide levels we see today have not been seen in at least the last 800,000 years, where carbon dioxide levels have averaged somewhere between 200 to 300 ppm in that time (from what we can interpret from ice cores).
Modern day CO2 levels may not have been seen last on Earth since 15-20 million years ago.
Like the rate of warming, it’s the rate of CO2 increase (that has coincided with the warming trend) in a short period of time that raises questions and potential concerns
– The rapid increase of atmospheric CO2 has coincided with humans burning greater quantities of fossil fuels like coal, oil and natural gas (that release carbon when they are burnt)
– Based on all the lines of evidence (there’s several lines of evidence linking CO2 to global warming), studies, and data available, the current scientific consensus is that human emissions are the primary cause of the warming trend we have seen since 1880, and even more likely in the last 50 to 60 years
– Some reports indicate that if Earth’s climate was primarily being influenced by natural factors right now, the Earth would be cooling, not warming.
The Earth was in a cooling period for the last 6000 years before the current warming trend
– Determinations of the Earth’s temperature history since 1950 have been measured with satellites and balloons, and in 1850, thermometers were being used.
Prior to that, we rely on Paleoclimatology studies and estimates based on proxy records such as tree rings, deep sea sediments, and so on
– Determinations of the Earth’s atmospheric CO2 levels in modern times have been measured at observatories since 1958.
But, prior to that for the last 10,000 years or so, we rely on Antarctic (and Greenland) ice cores.
Prior to that, ancient Earth data like tree rings, deep sea sediments, fossil leaves, and so on are studied
– The Earth is around 4.5 billion years old, and the climate and CO2 levels have varied throughout that time
– With both temperature and CO2 level interpretation of the Earth’s distant past, especially from hundreds of thousands of years ago, and millions of years ago or more, there can be some level of uncertainty, or inconclusiveness.
– Temperature or CO2 level estimates from more than a million years ago may be more qualitative and approximate, and only big signals or trends might be able to be identified, as opposed to detailed and precise temperature and CO2 signals and trends
– If we take geologic temperature records (such as deep sea sediments) for example, sometimes scientists can only classify temperature fluctuations from certain time periods as ‘likely’, because ‘evidence of temperature changes and glaciation is usually too scattered and sporadic to draw firm conclusions’ (wikipedia.org).
– Another example is determining global temperature records from 800,000 years ago with ice cores … with these ice cores, large-scale signals from the cores are clear, [but] there are problems interpreting the detail (wikipedia.org).
These are just two of many examples.
– Carbon dioxide levels from the past may also be in a similar category.
Some ice cores used in some studies interpreting carbon dioxide levels from 10,000 years ago are widely accepted.
Other studies that involve deep sea sediment, fossil leaves, and other proxies and ancient Earth data dating further back in time, may possess some level of approximation and uncertainty
– Additionally, CO2 levels and global average surface temperature are just two parts of the climate change picture (albeit, two important parts)
– There’s other factors that scientists and researchers observe, study, and interpret as part of climate change
– Scientists currently have modern technology set up such as satellites, sensors, buoys, gauges, and new technology that is being developed every year to observe and record various vital signs in the environment – carbon ppm, sea level, surface temperature, ocean temperature etc.
– Scientists also physically observe some of the suspected effects of climate change such as shrinking glaciers, retreating ice, changing animal and plant ranges, and so on
– Scientists have also run climate models simulating Earth’s past climate, and forecasting Earth’s future climate (although forecasting climate change in the future is an estimation only because of the variables involved).
Climate models run on and produce outcomes based on data, calculations, and assumptions fed into them by researchers/modellers.
So, some people question their use and are skeptical of them
– In addition to climate models having their limitations, there are other aspects of climate change contain a level of uncertainty (which we outline in the guide below)
One way to look at climate change might be:
1. What we definitely know,
2. What we think we know, and
3. What we have some uncertainty about or admit we don’t have a definitive answer for
Despite the limitations of interpreting climate change and uncertainties involved, some say these factors don’t remove the potential risk the potential future effects of climate change might pose to humans, the environment and Earth as a whole
Because of this perceived risk, a target of limiting future warming to below 2 degrees celsius above pre industrial levels (and more ideally, below 1.5 degrees) has been recommended to limit the potential negative impact
Solutions such as mitigation (peaking and bringing emissions to net zero, and absorbing and storing atmospheric carbon), and adaptation have been suggested.
Sequestration is another.
One of the key types of geographic areas we might focus on to reduce emissions is cities – where it’s estimated 70% of all emissions come from
Separate to the issue of climate change, we also know that mining and burning of fossil fuels is a major cause for other potential environmental and social issues.
Outdoor air pollution is a major example, and so is resource depletion (if fossil fuels become scarce)
Those critical of climate change might point to studies that indicate there are other climate drivers (other than CO2), or a range of other factors such as the limitations of climate models, or the way in which the ‘scientific consensus’ is developed and finalized
Someone who is undecided about where they stand in regards to the climate change issue might say they don’t know exactly what is causing a change in the climate, but they see that the climate that is changing physically in front of them, and they might support risk management measures such as decreasing emissions
Someone who is skeptical of climate change might point to the cost of the proposed solutions, limitations and drawbacks of the solutions (such as renewable energy, electric cars, and retrofitting buildings), as well as potential the potential impact on the economy and society of these solutions.
They may also point to the short timespan that most recent climate studies are based on, as well as the the uncertainties, limitations, flaws and inconsistencies in some data, studies and tools used to analyse climate change.
What Is The Main Question Posed About Climate Change?
Whether the recent warming trend we are seeing since 1880 (where global average surface temperature has increased 0.8 to 1 degree celsius up until 2019) is caused primarily by greenhouse gas emissions from human activities (mainly from the burning of fossil fuels), or whether it’s primarily from natural factors
What Is The Current Consensus On Climate Change?
There is currently a consensus (from different scientists, researchers and organisations around the world), based on all the lines of data and evidence available, that human emissions are extremely likely (greater than 95 percent probability) the main cause of the current climate warming trend over the last century or so (and natural factors are not)
Additionally, according to edf.org and skepticalscience.com:
Tens of thousands of scientists in more than a hundred nations have amassed an overwhelming amount of evidence that humans are the cause [and, these scientists and researchers come from different organisations – government, media, independent groups and researchers, science academies of all of the major industrialized countries, and so on]
… we are statistically more confident that humans cause climate change than that smoking causes cancer
Natural contributions may influence climate over shorter periods of say a decade, but, it is thought that at least over the last century, human emissions have had the greatest influence on the climate on longer time spans.
Some might question whether this time period is too narrow or short considering how old the Earth is
Definition Of Climate Change
Climate change is a change in the pattern of weather, and related changes in oceans, land surfaces and ice sheets, occurring over time scales of decades or longer [usually at least 30 years or more]
[Climate can be contrasted with weather which is] the state of the atmosphere—its temperature, humidity, wind, rainfall and so on—over hours to weeks.
It is influenced by the oceans, land surfaces and ice sheets, which together with the atmosphere form what is called the ‘climate system’
So, the weather is part of what makes up the climate.
Some people unofficially describe the climate as the weather averaged out over the period of decades to centuries.
Definition Of Global Warming
Global warming is a long-term rise in the average temperature of the Earth’s climate system, an aspect of climate change shown by temperature measurements and by multiple effects of the warming
So, global warming is one aspect of climate change.
A Key Measurement Of The Earth’s Warming – Global Average Surface Temperature
When sources refer to the warming trend, they usually reference …
Global average above land surface temperature – which is the temperature of the air immediately above the ground
[Sometimes, sources also refer to the] Sea surface temperature – which can either be the temperature of the air immediately above the ocean water surface, or of the top millimeter to top 20 metres of water in various parts of the ocean (depending on the methodology being used)
You can keep up with the global above land surface temperature at Nasa.gov
You can keep up with sea surface temperature at a site like Earthobservatory.nasa.gov
*Note that the global average is different to local regional averages.
How Much Has The Earth’s Climate Warmed In The Last Century Or So?
According to an ongoing temperature analysis … the average global temperature on Earth has increased by about 0.8° Celsius (1.4° Fahrenheit) since 1880.
Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade.
Since 1990, there are various sources that indicate we have had some of our warmest years on record when compared to the last century or so.
Earth’s global surface temperature in 2018 was the fourth warmest since modern record keeping began in 1880.
Global temperatures in 2018 were 1.5 degrees Fahrenheit (0.83 degrees Celsius) warmer than the 1951 to 1980 mean
Globally, 2018’s temperatures rank behind those of 2016, 2017 and 2015.
The past five years are, collectively, the warmest years in the modern record.
Eighteen of the 19 warmest years all have occurred since 2001, with the exception of 1998. The year 2016 ranks as the warmest on record.
What Makes The Recent Warming Trend Potentially Concerning?
There’s a few things, but just to note some of the main points:
– The period of warming has happened quite quickly (since 1880), and, even more quickly if you look at the period from 1950 or 1990 until the present day.
So, the fact that the rate of warming is relatively fast is a concern (it is thought that this rate of warming is unprecedented over decades to millennia)
– This rate of warming has coincided with an extremely quick rate of CO2 levels and concentration increasing in the atmosphere (from about 300ppm in 1950, to about 410ppm in 2019).
In the 800,000 years prior, studies indicate that CO2 levels rose and dipped between roughly 200 to 300ppm.
This rise in carbon closely mimics our burning of fossil fuels in the same time
– Based on natural climate factors, some sources say we should actually be in a cooling period now, and not warming (we were in a 6,000 year cooling period before we started this recent warming period in the last century or so)
– Some sources indicate that a rise in global temperature of 1 degree takes a huge amount of energy and heat being reflected back onto the Earth’s surface and oceans from greenhouse gas layers – pointing to how significant the impact humans have had on the Earth’s climate might be in such a short space of time
– Scientists think they have an idea of what was happening on Earth when rapid temperature change or abrupt climate change events happened in the past, and those events might be similar to what is happening now (huge and rapid carbon emissions, a big rapid jump in global temperatures, rising sea levels, ocean acidification, widespread oxygen-starved zones in the oceans etc.)
– In the past, some sources indicate that changes in Earth’s climate (usually drops in climate) of just 1 or 2 degrees celsius may have led to significant events that could have a significant impact of life on Earth for humans (a plunge into a freezing ice age for example)
– Continued warming and continued GHG emissions at the current rate increases the risk that Earth’s climate reaches a point where feedback processes and loops continually warm the Earth, no matter how much humans reduce their emissions – essentially, once we pass a certain threshold, we may no longer be able to do anything to keep the climate on Earth at safe levels anymore (which could mean our survival or well being as a species is in question)
An Asterisk On The Recent Warming Trend: … A Short Period Of Cooling Amongst The Long Term Warming Trend
Over the long term since 1880 to the present, global average surface temperature has risen.
But, there has been some short term cooling too.
… there was a period, roughly from 1998 to 2012, where the Earth’s global average temperature did cool temporarily.
It it thought that various natural factors such as La Niña events were part of the cause of this cooling … shifting some excess heat into the ocean
It is generally thought that natural factors can influence the Earth’s climate over the course of one or several decades, but non natural factors are responsible for long term climate impact (at least in the last century or so).
Another explanation of the above is:
The rate of average surface warming has slowed since 2001 (because decadal variability in the ocean-atmosphere system has redistributed heat in the ocean, and several temporary global cooling influences have come into play including unusually weak solar activity, increased aerosol production, and volcanic activity), but globally averaged near-surface air temperature (global average temperature) rose by around 0.8°C between 1850 and 2012
Global vs Regional Climate Change
There is a difference between global and regional climates and averages.
Regional climates tend to be subject to local weather patterns, and other unique local factors.
Global climate however, takes into account average temperature over the entire surface of the planet.
This is why the Earth’s average temperature can be rising, while some local regions of the world and parts of a country may be experiencing either cooling or warming.
What Is The Significance Of The Year 1880?
1880 is when modern record keeping started for Earth’s global surface temperature [observations did not sufficiently cover enough of the planet prior to that time]
This is also roughly around the time (1870) the second industrial revolution is recognised as having started in the US, and also when humans began burning/consuming fossil fuels like coal, oil and natural gas at a greater rate (this really increased around 1950 too).
What Is The Significance Of The 1950-1980 Baseline/Mean?
The period of 1951-1980 was chosen largely because the U.S. National Weather Service uses a three-decade period to define “normal” or average temperature.
The GISS temperature analysis effort began around 1980, so the most recent 30 years was 1951-1980.
It is also a period when many of today’s adults grew up, so it is a common reference that many people can remember.
Has Earth’s Climate Changed Before, And, How Much Has Earth’s Climate Warmed Throughout History?
Yes, Earth’s climate has changed throughout history.
There’s been various periods where the climate underwent different activity in terms of warming and cooling.
Since 1850, there has been a relatively quick rate of warming.
Other studies on things such as ice cores and more ancient Earth material might indicate:
The last 20,000 years or so has been unusually stable, with gradual warming in that period after coming out of an ice age.
The last 800,000 years has been categorised by recurring ice ages consisting of glacials (cooling) and interglacials (warming).
Prior to that, there was an extended ice age, and prior to that, Earth’s climate could be more unpredictable.
For the most climate activity from the past, scientists think they have a good idea of the factors influencing the climate during a specific time period.
Read more in this guide:
What Earth’s Climate Was Like In The Past: Last Century, Thousand, Million & Billions Of Years (Earth Climate History Timeline)
How Fast Did The Earth’s Climate Change In The Past, & What Are Abrupt Climate Change Events?
Earth’s climate has varied and changed at different rates through different periods in it’s 4.5 billion year history
Abrupt climate change is a significant change in the climate over the course of a few years, a decade, or a human lifetime i.e. a much quicker change than gradual change over decades, centuries and millennia.
It’s thought there has been several abrupt climate change events over Earth’s history.
Although, our ‘scientific understanding of abrupt climate change is considered to be poor’ (wikipedia.org)
It’s thought an abrupt climate change event is unlikely in the future for at least for the next century.
Reducing our emissions as quickly as possible and slowing down the rate of current climate change might be the best ways to prevent an abrupt or rapid climate change event.
Read more in this guide about how fast Earth’s climate changed in the past, and also about abrupt climate change events.
How Do We Know What Earth’s Temperature History Was?
The most detailed information about the global temperature exists since around 1850, when newer and more advanced thermometer, and satellite and balloon temperature measuring technology has since been used.
Prior to 1850, temperatures have either been estimated or studied.
The methods or data used to get an idea of temperature at different times are:
1950’s to now – Satellites and balloons
1850 to now – Thermometers
1000 to 2000 years ago – Tree rings and ice cores, and indirect historical proxies (records and reports from humans at that time)
12,000 years ago – Paleoclimatology studies and estimates
800,000 years ago – Ice cores [large scale signals are clear, but specific detail has interpretation issues]
Millions of years ago – Geologic evidence [such as sediment cores]
Read more about these time periods and methodologies and data used to understand global temperature record in this Wikipedia.org resource
What Factors Cause Earth’s Climate To Change?
There’s many factors, natural and man made, that can impact and influence the Earth’s climate.
Some of these are:
The Earth’s orbit in relation to the sun
The brightness of the sun (solar variations/fluctuations are thought to currently have only a very small contribution to recent warming – only a few percent, science.org.au)
Volcanic eruptions (small and large eruptions – the current contribution to atmospheric CO2 by volcanic activity is thought to be only around 1% of human emissions, science.org.au). Volcanoes also put aerosols into the atmosphere
The natural level of greenhouse gases in the atmosphere (CO2, methane, nitrous oxide and so on),
The ozone layer,
Stratospheric water vapour,
Methane release from termite mounds and other sources,
How reflective the Earth’s surface is (which can be impacted by the level of snow cover for example),
And, natural factors involved in the carbon cycle such as the absorption of CO2 in the atmosphere by soil and plants
Non Natural (Human) Factors
Release of greenhouse gases (like carbon dioxide) from the burning of fossil fuels (for electricity generation and transport, being big sources)
Release of black carbon pollution, more commonly referred to as soot (ucsusa.org)
And changes to land cover such as deforestation (deforestation is the second major human cause after the burning of fossil fuels), agriculture (emissions such as methane and nitrous oxide, but also clearing of land for agricultural use), and land use
Skeptical Science provides a graph of the radiative forcing impact of various factors between 1750 and 2005
They list the various radiative forcings as:
Surface Albedo (how reflective the earth’s surface is)
The Ozone (depletion can impact the ozone layer)
Stratospheric Water Vapour
They mention that 1) CO2 is the most dominant radiative forcing, and 2) CO2 radiative forcing is increasing faster than any other forcing.
There’s also a graphic available here that shows human contributions to warming far outweighing natural contributions in the last 50 to 60 years
At different points in the Earth’s timeline/history, different factors can be impacting the climate, with different variables to consider.
That’s why what is impacting the Earth’s climate today might be different than 40 million years ago (because of variables like the brightness of the sun, because of man made emissions, etc.).
On the different factors influencing climate during different time periods:
… comparisons of present day climate to periods [when CO2 levels were the same or higher than now] need to take into account that the sun was less active than now … When the sun is less active, the CO2-ice threshold is much higher.
Specific events that may have triggered or impacted abrupt climate events from Earth’s history might have included huge volcanic eruptions, changes in ocean currents and ocean circulation patterns (thermohaline circulation), collapse of ice sheets, and release of methane from frozen methane ices at the bottom of the ocean.
What Are Greenhouse Gases?
Greenhouse gases occur naturally and through human activities.
The primary greenhouse gases in Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone.
There are also the the ‘F’ gases, such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs)
What Is The Greenhouse Gas Effect, & The Carbon Cycle?
Greenhouse gases, and carbon dioxide especially, are responsible for the greenhouse effect, whereby these gases rise to the top of the atmosphere, and reflect and re-emit some infrared radiation back to the Earth’s surface – warming the Earth.
The greenhouse effect is a natural process (that humans actually need for Earth to be habitable and not freezing), but increased GHG emissions from humans accelerates or amplifies this effect, and carbon is released into the atmosphere faster than it can be absorbed by other parts of the natural carbon cycle (emissions outpace and are out of balance with carbon ‘sinks’ like oceans, plants and soils).
The movement of carbon between large natural reservoirs in rocks, the ocean, the atmosphere, plants (through photosynthesis, respiration and decay), soil and fossil fuels is known as the carbon cycle.
It’s worth noting that the concentration of water vapor in the atmosphere is not influenced directly by human activities, but rather influenced indirectly through by the production of carbon dioxide.
Water vapor has a much shorter lifetime compared to CO2, and it can be harder to measure the concentration of water vapor in the atmosphere compared to CO2.
What Are The Sources Of Greenhouse Gas Emissions?
GHGs can occur naturally in the atmosphere through various sources, such as the natural carbon and nitrogen cycles, volcanic eruptions, and other natural processes and events.
You can read more about how some of the natural sources of greenhouse gases work here
But, man made greenhouse gas sources are the main area to be concerned about.
Sources of greenhouse gases from humans vary depending on if you are talking about the city, country or global level.
Mainly, greenhouse gases from humans are caused by the burning of fossil fuels such as coal, oil and natural gas (in that order).
Fossil fuels are the major human cause of increased CO2 levels, with deforestation the second major cause (wikipedia.org)
… 87 percent of all human-produced carbon dioxide emissions come from the burning of fossil fuels like coal, natural gas and oil.
The remainder results from the clearing of forests and other land use changes (9%), as well as some industrial processes such as cement manufacturing (4%).
Electricity production, transportation, and the industrial sector tend to be big emitters of carbon dioxide.
Agriculture and land use is a big emitter of methane and nitrous oxide (from fertilizer, livestock, manure, and rice paddy crops).
Forestry is a carbon sink – which is why deforestation and land clearing can be a problem (amongst other issues like loss of biodiversity and land degradation).
As mentioned above, each city and country is different in terms of the greenhouse gas profile they have (i.e. which gases are emitted, from which sectors/industries or activities, and in which quantities).
You can read more about specific industries, countries and cities that emit greenhouse gases in different quantities and %’s further below.
Developing countries might have different GHG profiles to developed countries.
On the global level – you are really taking the average of all countries, so there’s limited specific information you can take from this.
Each fuel or energy source – coal, oil, natural gas, nuclear, renewables etc. – has it’s own carbon footprint and carbon intensity to consider, and even each different type of fossil fuel emits carbon at different rates (natural gas is usually the cleanest and coal the dirtiest, but it can depend on different factors)
More Information On Greenhouse Gases
Read more about greenhouse gases in this guide:
Which Greenhouse Gas Is The Worst?
How Long Do Greenhouse Gases Stay In The Atmosphere?
Which Greenhouse Gas Traps The Most Heat & Is Most Potent?
Which Greenhouse Gas Is Emitted The Most?
What About Aerosols?
Aerosols are not greenhouse gases.
They mainly have a cooling effect, but some of them can contribute to warming.
Human activities are … increasing aerosols in the atmosphere, which reflect some incoming sunlight.
This human-induced change offsets some of the warming from greenhouse gases
There is only one aerosol — soot, also known as black carbon — that actually helps contribute to global warming by boosting the warming effects of greenhouse gases in the atmosphere
[Aerosols aren’t necessarily a good thing because they can have human health effects, and can impact other things like rainfall]
Why Is Carbon Dioxide The Most Important Greenhouse Gas To Track & Monitor?
There are probably three main reasons:
1. Mainly because of the sheer quantity of it that we emit annually (mainly from burning fossil fuels like coal, oil and natural gas) compared to other GHGs
2. Because of how long carbon dioxide stays in the atmosphere once it is emitted before levels reduce (and therefore, it can impact climate change over a much longer duration than other climate drivers and greenhouse gases)
3. And, because increased CO2 leads to more water evaporating into the Earth’s atmosphere, which increases the temperature of the planet.
The higher temperature atmosphere can then hold more water vapor than before
CO2 is responsible for more of an increase in the amount of energy (and therefore heat) reaching Earth’s surface than the other greenhouse gases, even though other gases have more potent heat-trapping ability (global warming potential – GWP) per molecule than CO2 (e.g. over a 100 year time scale, methane might have a 23 to 28 times higher global warming effect compared to CO2).
In total, CO2 has the highest positive RF [radiative forcing] of all the human-influenced climate drivers compared by the IPCC [and positive RF’s indicate warming as opposed to cooling]
After a pulse of CO2 is emitted into the atmosphere, 40% will remain in the atmosphere for 100 years and 20% will reside for 1000 years, while the final 10% will take 10,000 years to turn over.
Water vapor has a short cycle in the atmosphere (10 days on average) [but, water vapor follows on from CO2 and creates a vicious warming cycle with the more CO2 that is added to the atmosphere]
Carbon dioxide is the largest single contributor to human-induced climate change.
NASA describes it as ‘the principal control knob that governs the temperature of Earth’.
Although other factors (such as other long-lived greenhouse gases, water vapour and clouds) contribute to Earth’s greenhouse effect, carbon dioxide is the dominant greenhouse gas that humans can control in the atmosphere.
Scientists have determined that, when all human and natural factors are considered, Earth’s climate balance has been altered towards warming, with the biggest contributor being increases in CO2.
[Water vapor is] the most abundant and powerful greenhouse gas in the Earth’s atmosphere [and] Water vapour accounts for around half the present-day greenhouse effect [but, most water vapor is released into the atmosphere naturally] via evaporation from the oceans [compared to the vast amounts of CO2 released and emitted by humans]
What Are CO2 Levels (PPM) Right Now?
CO2 levels today in 2019 are 411 ppm.
You can keep track of current CO2 ppm levels at Nasa.gov
How Much Have CO2 Levels Increased Recently?
Global annual mean CO2 concentration has increased by more than 45% since the start of the Industrial Revolution, from 280 ppm during the 10,000 years up to the mid-18th century to 415 ppm as of May 2019.
The present concentration is the highest for 14 million years (wikipedia.org)
What Have Been Carbon Dioxide Levels Throughout Earth’s History?
You can read more about carbon dioxide levels throughout Earth’s history here:
A History Of Earth’s Carbon Dioxide Levels Over Time (Carbon Dioxide Level Timeline), & How Fast CO2 Levels Are Increasing
What scientists and researchers think from looking at ice cores and ancient data samples of CO2 levels is that today’s CO2 levels are higher than at any point through the last 800,000 years.
Over the last 800,000 years, it’s thought CO2 levels fluctuated between about 200 and 300ppm, before significantly increasing up to today’s levels.
You can look at a graph of the last 800,000 years of CO2 levels at Nasa.gov
Where Do CO2 Emissions From Humans End Up?
There’s two major places CO2 emissions from humans end up:
‘Between 30% and 40% of the CO2 released by humans into the atmosphere dissolves into the oceans, wherein it forms carbonic acid and effects changes in the oceanic pH balance’ (wikipedia.org)
Currently about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere (wikipedia.org)
Other reports indicate that a large amount of carbon ends up in vegetation such as trees and forests, and also soils.
Are Ice Cores Reliable/Accurate?
Ice cores have been taken from ice sheets worldwide, but also from Greenland and Antarctica specifically.
Generally, for finding out accumulation, air temperature and air chemistry from another time in Earth’s history, they can be reliable:
Ice cores provide detailed records of carbon dioxide, methane and nitrous oxide going back over 650,000 years.
Ice core records globally agree on these levels, and they match instrumented measurements from the 1950s onwards, confirming their reliability.
Carbon dioxide measurements from older ice in Greenland are less reliable, as meltwater layers have elevated carbon dioxide (CO2 is highly soluble in water).
Older records of carbon dioxide are therefore best taken from Antarctic ice cores.
… [although] ice cores can also have other complexities
Are Climate Models Reliable?
Climate models can tell us certain things, but do have limitations and uncertainties in telling us other things.
Model supporters will say that although they aren’t perfect, they have gotten far more better and accurate over the years, and are great at identifying overall trends (they may also say model contrarians are yet to produce a model of their own that successfully models past climate change).
Model contrarians may say models don’t match up exactly with what is happening in reality, that they use calculations and formulas that serve to confirm the models’ creators beliefs, and that they haven’t been accurate in the past in forecasting future climate change.
Models also can’t yet predict abrupt climate change events.
The best way to view the use of climate models might be as one line of evidence and information among many lines of evidence and information across the climate change/global warming topic (so, they aren’t the one thing to rely on in making a conclusion about climate change, but, one of many pieces of evidence or one of many tools to understand the current data and information).
A summary of current day climate models might be:
While there are uncertainties with climate models, they successfully reproduce the past [by successfully reproducing temperatures since 1900 globally, by land, in the air and the ocean] and have made predictions that have been subsequently confirmed by observations
Models have evolved to the point where they successfully predict long-term trends and are now developing the ability to predict more chaotic, short-term changes
… Models don’t need to be exact in every respect to give us an accurate overall trend and its major effects – and we have that now.
If you knew there were a 90% chance you’d be in a car crash, you wouldn’t get in the car (or at the very least, you’d wear a seatbelt).
To wait for 100% certainty before acting is recklessly irresponsible.
… climate models are not good predictors of specific climate effects, such as the melting of Arctic sea ice or the frequency of major hurricanes in the north Atlantic
… There are two types of widely used climate models: large, complicated, planetary-scale models [also known as general circulation models] … and [smaller] higher-resolution models
… general circulation models are more accurate for long-term, worldwide forecasts, including the key measure of climate sensitivity—the amount of warming, in global mean temperature, that will happen when the amount of carbon in the atmosphere doubles from pre-industrial levels.
… The smaller, high-resolution models are better for examining the likely regional effects of climate change.
… models continue to get better … in the sense that they simulate many processes more realistically … But most climate scientists acknowledge that there are limits: no matter how sophisticated our models become, there will always be an irreducible element of chaos in the earth’s climate system that no supercomputer will ever eliminate
[developing better climate models has not helped] … in decreasing the uncertainty in future projections
Resources that outline some of the limitations or flaws with climate models are:
A list of the various flaws and errors with modern climate models (hoover.org)
Climate model results might conflict with one another, diverge from observations, and might not be fully rooted in established physics (notrickzone.com)
Climate models and reality vary (wattsupwiththat.com)
What Determines The Maximum Temperature Rise For Climate Change?
Maximum temperature rise (and subsequently the probability of limiting warming to 1.5°C) is determined by …
1) cumulative net CO2 emissions and …
2) net non-CO2 radiative forcing due to methane, nitrous oxide, aerosols and other anthropogenic forcing agents
What Are The Other Lines Of Evidence To Link Humans As The Primary Cause Of Recent Global Warming?
Some of the key questions that might have to be answered to validate the consensus on climate change might be:
Prove there is an amplified non natural change in the climate occuring, and that the change isn’t part of natural climate activity or natural climate variables
Identify the primary causes/sources of this amplified non natural change, and link the causes to the change
Identify the effects of this amplified non natural change, and link the effects to the change
Essentially – prove there are changes occuring in the climate caused by human factors, and that these factors wouldn’t be occurring if only natural factors were present.
Also, you have to link the non natural/human factors to the changes.
There’s a few good resources by edf.org and skepticalscience.com that lists some of the various lines of evidence that help establish a link of humans to the recent warming trend:
There are nine main independently studied, but physically related, lines of evidence (research on some of these lines began as early as the 1800’s) …
1. Simple Chemistry
[we know that burning carbon based materials emits CO2]
2. Basic Accounting
[we know how much fossil fuels we’ve burnt, and therefore how much CO2 we’ve emitted]
3. Measuring CO2 Levels
[we can measure levels of CO2 in the atmosphere through modern technology … as well as obtain CO2 levels from the past through ancient forms of Earth data – ocean sediments, tree rings, ice cores (from Antarctica, Greenland and tropical mountain glaciers), coral reefs, layers of sedimentary rocks, and compare CO2 levels throughout different time periods – some sources indicate that the amount of CO2 has risen drastically in the last 150 years].
Ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming (climate.nasa.gov)
4. Chemical Analysis
Of atmospheric CO2 that reveals the increase in CO2 is coming from burning fossil fuels
5. Basic Physics
[shows us that CO2 absorbs heat]
6. Monitoring Climate Conditions
To find that recent warming of the Earth is correlated to and follows rising CO2 emissions.
Additionally, from skepticalscience.com: ‘Throughout earth’s history, earth’s climate conditions and temperature have changed almost in unison with changes in carbon dioxide and greenhouse gas levels (i.e. as GHGs increase, temperature increases and as GHGs decrease, temperatures decrease).’
7. Ruling Out Natural Factors
That can influence climate like the sun and ocean cycles. From royalsociety.org ‘In order to discern the human influence on climate, scientists must consider many natural variations that affect temperature, precipitation, and other aspects of climate from local to global scale, on timescales from days to decades and longer … Examples include the El Niño Southern Oscillation (ENSO), and volcanoes … Scientists routinely test whether purely natural changes in the Sun, volcanic activity, or internal climate variability could plausibly explain the patterns of change they have observed in many different aspects of the climate system … These analyses have shown that the observed climate changes of the past several decades cannot be explained just by natural factors.’
8. Employing Computer Models
To run experiments of natural versus human-influenced simulations of Earth (models use calculations, formulas, data and assumptions fed into the models by humans).
Additionally, using climate models, it is possible to separate the effects of the natural and human-induced influences on climate.
Models can successfully reproduce the observed warming over the last 150 years when both natural and human influences are included, but not when natural influences act alone.
This is both an important test of the climate models against observations and also a demonstration that recent observed global warming results largely from human rather than natural influences on climate (science.org.au)
9. Consensus Among Scientists
Who consider all previous lines of evidence and make their own conclusions
Other lines of evidence might include …
– Measuring The Effect Of CO2
We can use satellites to compare how much energy is arriving from the sun, and how much is leaving the Earth
– Measuring The Wavelength Of CO2 & Linking It To An Increasing Temperature
CO2 traps energy at very specific wavelengths, while other greenhouse gases trap different wavelengths.
In physics, these wavelengths can be measured using a technique called spectroscopy. When looking at the different wavelengths of energy, measured at the Earth’s surface, on a Spectroscopy Graph – among the spikes you can see energy being radiated back to Earth by ozone (O3), methane (CH4), and nitrous oxide (N20).
But the spike for CO2 dwarfs all the other greenhouse gases, and tells us something very important: most of the energy being trapped in the atmosphere corresponds exactly to the wavelength of energy captured by CO2 (skepticalscience.com)
Scientists do ‘fingerprinting’ which allows them to see whether natural or man made climate forcings are leaving their ‘fingerprints’ on the climate and environment.
From royalsociety.org ‘Observed atmospheric temperature changes show a fingerprint much closer to that of a long-term CO2 increase than to that of a fluctuating Sun alone’
Another couple of resources that discuss evidence linking human emissions to the change in climate are:
Why scientists think 100% of global warming is due to humans (carbonbrief.org)
Climate change evidence and causes (royalsociety.org)
In addition to spending time linking human causes/sources to a changing climate, scientists and researchers can observe the environment to try to link a changing climate to the effects of this change.
Some of those effects and observations might include:
Shrinking glaciers and ice sheets, glacial retreat, decreased snow cover, declining arctic sea ice, warming oceans, sea levels rising, ocean warming, ocean acidification (from the ocean absorbing CO2), extreme events like droughts, and more
There’s stats on these environmental observations and measurements available at several sources:
Climate change – how do we know? (climate.nasa.gov/evidence/)
Global temperature (climate.nasa.gov)
Sea level (climate.nasa.gov)
Climate Change Indicators: Sea Surface Temperature (epa.gov)
Some indicators to keep a track of in tracking climate change might be:
CO2 parts per million levels
Earth air surface temperature
What is clear from the above is that there isn’t just one piece of evidence or indicator when it comes to climate change.
There’s many pieces of evidence and many indicators that have to be analysed and linked together.
Classifying The ‘Effects’ Of Climate Change
‘Effects’ of climate change should really be classified as events or things that happen as a full or partial result of the recent climate warming trend (and this of course relies on the consensus that the warming trend is happening, and is happening primarily as a result of anthropogenic/human actions).
They may also be impacted in some way by the recent climate warming trend.
To put that another way – if the event would have happened exactly the way it did regardless of the recent climate warming trend – then, that event isn’t an effect of climate change, but rather an occurence of the natural climate and natural factors.
With this in mind, the question is how you can qualify or measure what events are linked to climate change, and which ones might not be.
The answer is that some events can clearly be linked to a changing climate.
For example, it can clearly be observed or proved with basic/widely accepted logic or calculations that the increased amount of carbon dioxide in the air is impacting a particular event (such as ocean acidification), or, that the increased surface temperature is impacting a particular event (such as it being too hot to grow certain agricultural crops effectively at a certain part of the year).
Another example is physically spending money (an economic effect) to adapt to, or address the effect of increased emissions or a warmer temperature in one region.
The problem is that other events may be far more subjective, or involve calculating a level of probability they are linked to or amplified ro diminished by climate change (i.e. you are relying on a % of probability, and not a near certainty – it’s essentially a speculative or inconclusive link).
One example of this is using a model or evaluation calculation to calculate the probability that a changing climate is increasing the probability of extreme weather events like droughts.
The following two reports discuss the ‘probability’ that Cape Town’s past significant drought was linked to climate change.
They indicate that there’s some level of probability that some droughts are made up to 3 times more likely with every 1 degree celcius that global average temperature warms:
Global warming has already raised the risk of more severe droughts in Cape Town (theconversation.com)
Why Cape Town’s drought was so hard to forecast (theconversation.com)
Event attribution studies are one way that events are analyzed to establish a link to the changing climate.
Effects & Impact Of Climate Change
Some effects are said to have already taken place (such as sea level rise).
Effects that scientists had predicted in the past would result from global climate change are now occurring: loss of sea ice, accelerated sea level rise and longer, more intense heat waves.
Others are forecast for the future (and there can be a level of uncertainty in predicting future events).
The effects can be environmental, but may also directly or indirectly impact humans (and human health), wild life, plant life and living organisms, as well as the economy.
There’s essentially an impact on all areas of the natural and non natural world.
Some effects can be negative, whilst others can be positive, and, some effects can happen worldwide, whilst others happen in specific geographic locations and regions.
With every increment of increased temperature, the effects are projected to change:
There are some significant differences between the risks and impacts on people, animals, the environment and earth overall when going from 1.5 degrees to 2 degrees warming (report.ipcc.ch)
Commonly listed effects of climate change may include, but aren’t limited to:
Rising surface temperature
Warming oceans, and lakes (in some cases, faster than the surrounding environment – Lake Superior is one example, according to livescience.com)
Shrinking ice sheets, loss of ice and ice breaking up earlier than usual (at both polar ice caps)
Glacial retreat and shrinkage
Decreased snow cover
Sea level rise
Declining Arctic sea ice
Changing the frequency, duration and intensity of extreme weather events [natural events like droughts, floods, storms, hurricanes, heatwaves]
Ocean acidification [due to increased carbon levels] – ‘Between 30% and 40% of the CO2 released by humans into the atmosphere dissolves into the oceans, wherein it forms carbonic acid and effects changes in the oceanic pH balance’ (wikipedia.org)
Changes in the natural water hydrological cycle – Perth, Australia is an example of a location where this may have already happened because of a changing climate
Changes in rainfall (precipitation) patterns – Australia’s annual average rainfall has increased in the last century, but several regions have seen a substantial decrease since 1960
Changes in wind patterns
Land subsidence/land sinking to increase in the future
Flooding of coastal and sea side land to increase in the future
Arctic Ocean to become ice free in the future – we’ve put together a separate guide on ice melt and ice loss in the future
Increasing wildfire, insect outbreaks and tree diseases in the future
Potential abrupt climate change events
The possibility of an abrupt shift in the climate system is only one feature of a changing climate that is expected to become more erratic, with extreme weather events like droughts, torrential rainfall, and extreme heat becoming more common (ucsusa.org)
Animals & Plants
Animal migration patterns changing
[The impact of CO2 stimulation of plant life and crop growth can be unclear – it might vary by species, might vary by greenhouse and field plants, and may also have positive effects on some nutrients in crops whilst negatively affecting other nutrients] (wikipedia.org)
Plants changing the dates of activity, such as trees budding their leaves earlier in the spring and dropping them later in the fall (livescience.com)
Frost free and growing seasons lengthening
Both animal and plant ranges have shifted
Altered conditions (temperature and rainfall) for plant life and crops to grow
Humans & Human Health
Humans overall rely on a stable climate for many things – the water we drink, the food we eat, the clothes we wear, the businesses and industries we work in, and so on
Changes to availability of usable water supplies
Changes to agricultural production and food security
Infrastructure, agriculture, fisheries and ecosystems will be increasingly compromised in the future
The groups of people that will see the initial and most significant impact from global warming, and an increase in maximum temperature are vulnerable and disadvantaged groups – less developed countries, regional, island, coastal, dry region, some indigenous and other populations
Some less developed countries and island countries could be most at risk of feeling the impacts of climate change first (due to rising sea levels and not being able to invest in mitigation or adaptation strategies)
Climate change is boosting flood risk in southern England
The consequences will worsen as temperatures climb further.
And with those facing the greatest risks often the least able to absorb the damage, climate change is expected to exacerbate economic inequalities and erode progress on reducing poverty
Event attribution studies have shown that rising temperatures doubled the risk of the torrential rains behind the Louisiana floods last August and that climate change was responsible for 70% of heat-related deaths in Paris during the 2003 heatwave.
Some of the cost of climate change might be:
Costs to adapt to climate change
Costs to reduce emissions and prevent further
Costs to address the effects of climate change that have already happened
Present and future lost economic value caused by changes in water supply (that we use for households, business and agriculture), changes to particular industries like agriculture, and degradation of natural resources
Some reports may indicate that it’s hard to measure the potential impact of climate change on the economy.
Other reports make some estimates.
The share of national GDP at risk from climate change exceeds $1.5 trillion in the 301 major cities around the world. Including the impact of human pandemics – which are likely to become more severe as the planet warms — the figure increases to nearly $2.2 trillion in economic output at risk through 2025
… climate change has cost the U.S. economy around $240 billion per year over the last 10 years.
… another report … found that the U.S. economy will contract by up to 10 percent by the end of the century if climate change continues at its current pace.
These economic losses are the result of extreme weather events, worsened air quality, rising sea levels and other effects
While it’s hard to pin a dollar value on damages, economic models suggest climate change already costs hundreds of billions in damages globally during the 20th century through lost crops, rising seas and more extreme weather.
There’s already been loss and damage from climate change, and there will be into the future.
Loss refers to things that are lost forever and cannot be brought back, such as human lives or species loss, while damages refers to things that are damaged, but can be repaired or restored, such as roads or embankments
According to the IPCC, ‘Net annual costs will increase over time as global temperatures increase’ and ‘the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time’
Read more about potential economic impacts of climate change at wikipedia.org
In addition to the above general effects of climate change, each country and region within a country may experience their own specific effects.
For example, wwf.org.au outlines some of the effects in Australia (effects may differ State to State) relate to weather, extreme events, weed and pest invasion, salt invasion, threatening of the Great Barrier Reef, threatening species extinction because of habitat destruction and environmental change, food and farming, water, coastal erosion, health issues (related to heat waves and increased humidity leading to more mosquito-borne disease), damage to homes, and coral bleaching.
Read more about possible future effects of climate change, and effects observed so far in the US at climate.nasa.gov/effects/
Consider this from ucsusa.org:
… warming has caused changes in rainfall—some regions have become wetter while others have become drier—and droughts and severe rainfall events have become more common.
As we rapidly increase Earth’s average temperature, some regions, such as high latitudes, will experience greater warming than others, such as the tropics.
As warming alters ocean and atmosphere circulation patterns, some regions could even experience cooling.
Future Effects Could Be Better Or Worse Than Forecast
According to the IPCC, the extent of climate change effects on individual regions will vary over time and with the ability of different societal and environmental systems to mitigate or adapt to change … [and there will be] beneficial impacts in some regions and harmful ones in others i.e. climate change could prove to be less severe than current estimates, but could also prove to be worse
Forecasted Future Effects Of Climate Change
Some of the forecasted future effects of climate change are available here:
- In the IPCC’s Fifth Assessment Report (AR5) – http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_FINAL.pdf
Note though – forecasted effects are not a certainty – they are simply an estimate or approximation.
A recent events attribution study worked out that a repeat of the severe floods caused by Hurricane Sandy in 2012 could be up to 17 times more likely by 2100, for example.
What Happens At Each Degree Of Warming In The Future? (Impact At 1.5, 2, 3, 4 & 4+ Degrees Celsius)
The difference in impact for each degree warming in the future might be seen in:
Sea level rise
Temperature of the ocean
Ice in the Arctic
Thawing of permafrost
Size of glaciers
Snow in the northern hemisphere and around the world
Exposure to heat waves
How warm it is over the land
Cold extremes over land
Number of consecutive dry days
Number of consecutive days with rainfall
Intensity of rainfall
Frequency of rainfall extremes over land
Average river flows
Average drought length
Population introduced to water scarcity
Population exposed to drought
Number of tropical cyclones
Number of 4 and 5 category cyclones
Coastal areas flooded
Crop yields for wheat
Crop yields for maize
Crop yields for soy
Crop yields for rice
Plants, and animal species losing their climatic range
Average warming across drylands and humid lands
Global per capita GDP and other GDP related factors
Transmission of diseases like malaria
Other human health related factors
Carbon Brief has extracted data from around 70 peer-reviewed climate studies to show how global warming is projected to affect the world and its regions.
At different temperature levels (1.5 degrees, 2 degrees, and higher), you can see the impact of temperature levels on:
Oceans, Ice, Rainfall & Precipitation, Drought, Storms & Flooding, Crops, Nature/Animals, Plants, The Economy, Health
The World/Globally, Europe, The Americas, The Caribbean & Small Islands, Africa, Asia, China, Australasia
View the full interactive chart at https://interactive.carbonbrief.org/impacts-climate-change-one-point-five-degrees-two-degrees/
The IPCC Summary For Policymakers also outlines the potential differences of impacts between 1.5 and 2 degrees celsius warming/temperature change.
You can read more at http://report.ipcc.ch/sr15/pdf/sr15_spm_final.pdf
Other resources that outline potential impact at different degrees of warming:
- https://www.wri.org/ipcc-infographics (some impacts at 2, 2.9, 3.7 and 4.8 degrees celsius warming)
- http://globalwarming.berrens.nl/globalwarming.htm (degree by degree explanation of what happens when the earth warms – 1, 2, 3, 4, 5, and 6 degrees of warming)
- https://www.dw.com/en/the-world-at-3-degrees-what-it-means-for-five-cities/a-41392444 (the world at 3 degrees, and what it means for 5 cities)
- https://www.theguardian.com/cities/ng-interactive/2017/nov/03/three-degree-world-cities-drowned-global-warming (a 3 degrees world and which cities will be drowned by it)
- http://www.global-greenhouse-warming.com/3-degrees.html (3 degrees of warming)
- https://www.greenfacts.org/en/impacts-global-warming/l-2/1.htm (impacts of 4 degrees global warming)
- https://bigthink.com/strange-maps/what-the-world-will-look-like-4degc-warmer (what the world will look like 4 degrees warmer)
- https://theconversation.com/a-matter-of-degrees-why-2c-warming-is-officially-unsafe-42308 (why 2 degrees celsius warming might be considered unsafe)
Which Countries Emit The Most Greenhouse Gases?
You can read more in this guide about the countries that emit the most greenhouse gases
The United States has emitted to most cumulative greenhouse gases throughout history (as of the year 2019). You can read a summary of the United States’ greenhouse gas emissions here
China (in 2019) currently emits the most annual greenhouse gases (and leads the second placed United States by about double the quantity of annual emissions). You can read a summary of China’s greenhouse gas emission here
Read a Summary Of Global Greenhouse Gas Emissions in this guide
Different reports show different countries as leaders for per capita GHG emissions
There’s good graphs available at this resource showing emissions by different countries according to different measures – https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions
It’s important from the above to outline that there is a big difference between cumulative and annual greenhouse gas emissions.
Annual greenhouse gas emissions is obviously a reflection of which country has the biggest carbon footprint now – ‘[China] has had the world’s largest carbon footprint since 2004 and was responsible for 28.3 percent of global carbon dioxide emissions in 2017.’ (chinapower.csis.org)
China’s economic growth, industrial activity, size of population, and it’s use of coal are all thought to contribute to it’s annual carbon footprint.
In particular, it’s use of coal – ‘China still consumes more coal than the rest of the world combined’ (chinapower.csis.org)
Which Countries Emit The Least Greenhouse Gases?
You can read more in this guide about the countries that emit the most and the least greenhouse gases
Per capita, countries in central South America, the Middle East and both eastern and southern Africa [have some of the lowest national average emissions]
Per capita, Denmark, Finland and Nigeria were the lowest CO2 emitters in 2016
Which Countries Might Be Affected The Most By Climate Change & Global Warming?
… the countries most severely impacted by climate change contributed the least to greenhouse gas emissions
… highly vulnerable regions included central South America, the Middle East and both eastern and southern Africa.
Less vulnerable regions were largely in the northern part of the Northern Hemisphere
Note – a different question to ‘who might be most impacted by climate change’ would be ‘who is least able to adapt to climate change and who is therefore most vulnerable?’.
Poor and under developed countries are obviously at risk in this regard, as well as coastal and island regions (due to factors like sea level rise).
theconversation.com has a good piece available on the imported and exported carbon footprint from developing and poorer countries to developed and wealthier countries.
Their report indicates that richer nations must start making themselves more accountable for the carbon footprint in the materials and products they import from other countries.
Which Countries Might Need To Do More To Reduce Their Greenhouse Gases?
There’s various ways we might assess the countries that need to be doing more, or need to be making more of an effort, to do their ‘fair share’ to address climate change
You can read this guide which outlines countries that might need to do more to address climate change based on measures such as annual, cumulative, per capita greenhouse gas emissions, and more
Which Industries & Sectors Emit The Most Greenhouse Gases?
The different major emitting sectors and a description of each one might include:
Energy & Electricity Generation – the generation, transmission, and distribution of electricity
Transport – the movement of people and goods by cars, trucks, trains, ships, airplanes, and other vehicles. It involves road travel, but also air, rail, water, and so on. It can involve private vehicles, public vehicles, freight and delivery vehicles, and more.
Industrial – the production of the goods and raw materials we use everyday
Commercial and Residential – homes and commercial businesses. Excludes agricultural and industrial activities
Agriculture – crop production, livestock production, farms and ranches.
Land Use & Forestry – the management of land, the conversion in use of land, and forests and vegetation.
Other Sectors – there are also other sectors to consider.
Read more in this guide about the industries and sectors that emit the most greenhouse gases.
What is interesting to note is that emissions by industry can be measured by quantity of GHGs emitted, and also % share.
For example, agriculture in some countries might be responsible for the most nitrous oxide and methane emissions, but not CO2.
But, they can also be measured by CO2 intensity of each industry – and, according to some measures, transportation has the highest CO2 intensity.
There’s also direct and indirect emissions to consider from each industry.
Sectors like agriculture, industrial activity, residential and commercial, and even transport when considering electric cars, all have their own direct emissions, but also indirectly use electricity from power generation, which has an indirect emission footprint
Read more about potential solutions to addressing emission in each sector in these guides:
Read more about the different sectors in these guides:
Solutions For Addressing Climate Change In The Transport Sector
Solutions For Addressing Climate Change In Power & Electricity Production
Solutions For Addressing Climate Change In The Commercial & Residential Sectors
Solutions For Addressing Climate Change In Agriculture, Land Use & Forestry
Solutions For Addressing Climate Change In Industry
How Can We Track How Different Countries Are Managing Their Greenhouse Gas Emissions Over Time?
There are sites like climateactiontracker.org that provide various tracking indicators, methodology and forecasts to communicate how different countries are tracking with their greenhouse gas emissions over time.
Check out https://climateactiontracker.org/countries/ for more info.
Something that is important to note though is that some sources point out that some countries may report incomplete or inaccurate data on their true annual emissions i.e. some countries could be reporting far less emissions than what they are actually producing.
Cities As Significant Greenhouse Gas Emitters
Often, we look at emissions on the global or national/country level.
But, recent reports are starting to look at the significance of cities as emitters.
This guide outlines the basics of what to be aware of in regards to the carbon footprint of cities worldwide.
Which Cities Emit The Most Greenhouse Gases?
You can read more in this guide for the full list of cities that emit the most greenhouse gases in total, and per capita
In 2019 Seoul, Guangzhou and New York were the top 3 emitters in total GHGs
In 2019, Hong Kong SAR, Mohammed Bin Zayed City, and Abu Dhabi were the top 3 emitters in per capita GHGs
Which Cities Have Already Reduced Their Emissions?
As of 2019, there’s already 27 of the world’s biggest cities that have reduced emissions below 10% of what their peak emission quantity was.
You can read more in this guide about the cities that have reduced emissions, and in general, how cities can reduce emissions and address climate change.
How Can We Track How Different Cities Are Managing Their Greenhouse Gas Emissions Over Time?
One place you can go to see how some cities are tracking in terms of how they are addressing greenhouse gas emissions & sustainability is:
What Are The Recent Trends For Greenhouse Gas & Carbon Emissions?
Since 1990, Chinese emissions have increased significantly.
You can see total Chinese CO2 emissions since 1990 at:
Since 1990, gross U.S. greenhouse gas emissions have increased by 1.3 percent
You can see total US GHG emissions since 1990 at:
Global carbon emissions from fossil fuels have significantly increased since 1900.
Since 1970, CO2 emissions have increased by about 90%, with emissions from fossil fuel combustion and industrial processes contributing about 78% of the total greenhouse gas emissions increase from 1970 to 2011.
You can see total Global carbon emissions since 1990 at:
Target/Goal For Future Warming, & How We Achieve It
The Paris agreement set goals in limiting global warming to well below 2°C, and further pursuing efforts to limit it to 1.5°C (it’s expected the negative effects and impact of climate change will be less at 1.5°C, and adaptation will be easier too).
To keep global temperature rise below the agreed 2°C, global carbon emission must peak in the next decade [before 2030] and from 2070 onward must be negative
… warming will slow to a potentially manageable pace only when human emissions are reduced to zero
Other targets say emissions need to peak by 2020, and emissions need to hit zero by 2050.
This is the challenge our world leaders face.
To keep global temperature rise below the agreed 2°C, global carbon emission must peak in the next decade and from 2070 onward must be negative: we must start sucking out carbon dioxide from the atmosphere.
Despite 30 years of climate change negotiations there has been no deviation in greenhouse gas emissions from the business-as-usual pathway, so many feel keeping global warming to less than 2°C will prove impossible.
Projections & Forecasts For Future Warming
There is a graph showing a variety of projections for different pledges and policies by 2100 available at:
What the graph shows is that we are currently on track globally for warming in the range of 3 to 4 degrees with current policies.
But, more climate friendly policies can change that pathway to a lower temperature.
Using scenarios ranging from business-as-usual to strong longer-term managed decline in emissions, the climate model projections suggest the global mean surface temperature could rise by between 2.8°C and 5.4°C by the end of the 21st century.
Even if all the current country pledges submitted to the Paris conference are achieved we would still only just be at the bottom end of this range.
If there were no technological or policy changes to reduce emission trends from their current trajectory, then further warming of 2.6 to 4.8 °C (4.7 to 8.6 °F) in addition to that which has already occurred would be expected during the 21st century.
Projecting what those ranges will mean for the climate experienced at any particular location is a challenging scientific problem, but estimates are continuing to improve as regional and local-scale models advance.
It’s looking extremely unlikely that warming is limited below 1.5 degrees
At the current rate, we will hit 1.5 degrees between 2030 and 2052
Stringent mitigation policies might be able to limit global warming (in 2100) to around 2 °C or below, relative to pre-industrial levels.
Without mitigation, increased energy demand and extensive use of fossil fuels might lead to global warming of around 4 °C.
From the IPCC 4th Report – the best estimate for global mean temperature is an increase of 1.8 °C (3.2 °F) by the end of the 21st century.
This projection is relative to global temperatures at the end of the 20th century.
The “likely” range (greater than 66% probability, based on expert judgement) for the SRES B1 marker scenario is 1.1–2.9 °C (2.0–5.2 °F).
For the highest emissions SRES marker scenario (A1FI), the best estimate for global mean temperature increase is 4.0 °C (7.2 °F), with a “likely” range of 2.4–6.4 °C (4.3–11.5 °F).
The range in temperature projections partly reflects (1) the choice of emissions scenario, and (2) the “climate sensitivity”.
Different scenarios make different assumptions of future social and economic development (e.g., economic growth, population level, energy policies), which in turn affects projections of greenhouse gas (GHG) emissions.
[cumulative emissions are closely related to projected warming]
Without new policies to mitigate climate change, projections suggest an increase in global mean temperature in 2100 of 3.7 to 4.8 °C, relative to pre-industrial levels (median values; the range is 2.5 to 7.8 °C including climate uncertainty).
The current trajectory of global greenhouse gas emissions is not consistent with limiting global warming to below 1.5 or 2 °C, relative to pre-industrial levels.
Pledges made as part of the Cancún Agreements are broadly consistent with cost-effective scenarios that give a “likely” chance (66-100% probability) of limiting global warming (in 2100) to below 3 °C, relative to pre-industrial levels
Note though that projections are like climate budgets – they are an estimation only, and are subject to change in the future.
Warming may be greater or less than the current projections show.
Projections can change over time as different information becomes available and as variables change.
Emissions Pathways To Different Levels Of Future Warming
As a guide, some sources have formulated potential pathways to different levels of warming in the future.
wri.org shows an infographic that shows:
A Low emissions pathway that leads to 2 degrees warming
A Medium emissions pathway that leads to 2.9 degrees warming
A High emissions pathway that leads to 3.7 degrees warming
The Highest emissions pathway that leads to 4.8 degrees warming
View it here – https://www.wri.org/resources/data-visualizations/infographic-choose-your-future-4-possible-emissions-pathways
Limiting Warming To 1.5 Degrees – In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO2 emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range).
Limiting Warming To 2 Degrees – For limiting global warming to below 2°C CO2 emissions are projected to decline by about 20% by 2030 in most pathways (10–30% interquartile range) and reach net zero around 2075 (2065–2080 interquartile range).
[The IPCC report also shows pathways for achieving different levels of warming, and the potential effects at each level of warming]
Other pathway scenarios and data can be found at ourworldindata.org under ‘Future emissions scenarios’
Carbon Budgets – What Are They, & What Are Their Potential Limitations?
What Is A Carbon Budget?
A carbon budget expresses the remaining amount of carbon dioxide (or total greenhouse gases, expressed in CO2e) that can be emitted (in total, or per year) in order to increase the likelihood of limiting global temperature rise/warming to a certain amount above pre-industrial levels (usually 1.5 or 2 degrees)
If the carbon budget number is exceeded, there might be more of a chance that warming reaches a particular temperature.
Read more about calculating the carbon budget at wri.org
What Is The Current Carbon Budget?
The budget [was around] 1 trillion tonnes of CO2 [when it was developed, but as …] of 2011, we’ve already gone through 52% of the budget (wri.org)
When Will We Exceed The Budget, & How Can We Stay Within It?
wri.org has more information on the years we might exceed the budget, depending on different emission rates
For example, at the current rate of emissions, we might exceed the budget in the year 2045
wri.org also explains what actions the world might take to limit warming to below 2 degrees – peaking emissions by 2020 and decreasing emissions steeply each year after
If we are able to decrease CO2 emissions to zero by the year 2080, we might avoid 2℃ of global temperature increase, but would pass 1.5℃ before the year 2040
carbonbrief.org explains that (paraphrased) keeping warming below 1.5 degrees might be unlikely, but, global CO2 emissions need to get to net zero by mid century
How Much More Fossil Fuels Reserves Can We Burn To Stay Within The Carbon Budget?
If the world burned all of its currently known reserves [of fossil fuels] (without the use of carbon capture and storage technology), we would emit a total of nearly 750 billion tonnes of carbon.
[Based on the above figure …] we have to leave around two-thirds of known reserves in the ground if we want to meet our global climate targets … [and] if we wanted to increase the probability of keeping warming below two degrees celsius to 80 percent … [we …] would have to leave 75-80 percent of fossil fuels untouched
Potential Limitations With Carbon Budgets
Similar to a carbon footprint, a carbon budget might simply be a generalised tool.
It’s not a definitive number or calculation.
Several reasons for this might include:
Emission rates might change in the future (depending on how quick decarbonisation is)
Uncertainties to do with different aspects of climate change, such as exactly how much of each greenhouse gas being emitted leads to what exact level of global warming
It is important to keep in mind that the global ‘carbon budget’ [is really a simplification] … [and] there is actually a variety of possible carbon budgets [with] their size [depending on several factors] (ourworldindata.org)
The Carbon Budget Can Change/Be Revised Over Time By The IPCC
New IPCC reports have revised old budget numbers.
carbonbrief.org goes into more detail about how they’ve done this
For example, paraphrased, between the IPCC’s fifth assessment report (AR5) and the IPCC’s new SR15 report:
They actually increased the budget for a 50/50 chance of exceeding 1.5C warming by double from 268GtCO2 – or around seven years of current emissions, to 580GtCO2 – 14 years of current emissions.
The 66% chance of avoiding 1.5 degrees celsius warming scenario was also expanded from three years, to 10 years of current emissions
Although it’s worth confirming the exact numbers in the reports
What Are The Main Solutions To Addressing Climate Change & Global Warming?
Some of the major approaches to addressing climate change and global warming are:
Mitigation (bringing emissions to a peak point, reducing them incrementally, and eventually bringing them to net zero)
Sequestration & Storage (absorbing CO2 already in the atmosphere, and storing it in permanent geological, biological or oceanic reservoirs – science.org.au)
Adaptation (adapting to the changes/impact caused by warming)
Climate engineering (large-scale engineered modifications to limit the amount of sunlight reaching the earth, in an attempt to offset the effects of ongoing greenhouse gas emissions – science.org.au) is another option, although it does not form part of the main strategy at the moment and contains some uncertainties.
Specific Solutions & Ways To Address Climate Change & Reduce Emissions
Although there is a global target for future warming and some main solutions for climate change, each country, State/province, city, and sector need their own custom strategy and specific solutions.
Read more about specific solutions to climate change in this guide:
Solutions To Climate Change: Comprehensive Guide
One of the specific solutions suggested to reduce emissions is to use renewable energy as a greater share of power production to decarbonize the grid.
Regarding renewable energy, some sources indicate that ‘As of 2019, however, [renewable energy] needs to grow six times faster to limit global warming to 2 °C (3.6 °F)’ (wikipedia.org)
But, there’s also now a growing idea that renewable energy and other commonly suggested solutions like electric cars won’t be enough on their own and a decrease in overall consumption or the consumption rate might be a better primary solution (better energy production and usage efficiency is one way this can be achieved).
A growing world population (which means more demand for electricity, transport, food and agriculture, desalination plants etc.) and developing countries increasing their energy use from industrial development and growing their economies, may also add to future emission totals (although several major cities in the world have peaked and reduced emission in spite of growing populations and economic growth)
A single solution or single approach to addressing climate change won’t work – it needs to be multi tiered and there needs to be buy in from multiple cities, countries and key decision makers.
Additionally, some of the major solutions put forward like renewable energy and alternative fuel vehicles have practical and technological challenges of their own.
And, this is not to mention the financial, social and logistical challenges of researching, developing and implementing these solutions at scale on a macro level.
Some studies indicate that two thirds to 80% of fossil fuels currently in the ground have to be left there to limit warming to target levels.
Potential Challenges & Barriers To Implementing Mitigation & Adaptation Solutions Quickly, & At Scale
Although some cities have seen reductions already, global and national level solution implementation can have it’s potential challenges and barriers:
1. Different countries face different challenges to each other
Developed vs developing countries
Governments with economic growth as a priority or goal vs governments with the environment as a priority or goal
Hot/dry climate countries vs Wet climate countries
2. Different countries contribute differently to annual GHG % share, & put different amounts of effort into reducing emissions (ideally, effort should reflect emissions %)
3. It can be difficult to get all countries to agree and co-operate on targets (the US for example previously pulled out of the Paris Agreement)
4. Partnerships for solutions can be complex, and can involve multiple groups and levels government – makes organisation/planning and executing difficult
5. Countries less affected by climate change have less incentive to implement changes
6. Climate change may have to be addressed at the global, national, regional and local levels – which may involve different goals and solutions, and may conflict
7. Capital investment for solutions isn’t always available, and some changes may be too expensive even when it is (such as urban and infrastructure changes)
8. Investment, financing and access to loans isn’t always available
9. The final costs to implement mitigation and adaptation solutions are still unknown – leads to uncertainty and stagnation in implementing some changes
10. The costs to address and adapt to the after effects of climate change if we don’t reduce emissions are still unclear – and some people may be willing to gamble they aren’t too costly
11. Land use transition can be difficult
12. Modelled pathways to achieve 1.5 and 2 degrees and one degree warming might be unrealistic from a scale perspective in and in the time required – e.g. we can’t reduce fossil fuel use and switch to renewables or more carbon efficient energy systems in the time required on the scale required
13. Renewable energy like solar, and other solutions such as carbon dioxide removal aren’t feasible everywhere
14. Awareness and understanding of why specific solutions to climate change are required may not be high enough amongst politicians and the general public in order to support and implement necessary changes
15. Sustainable development and reduction of emissions may seem too difficult and costly vs regular development
16. Implementing solutions may involve certain enabling conditions being in place first in some instances (and these conditions aren’t always in place or able to be put in place)
17. There can be trade-offs to addressing climate change (even in lieu of benefits) – the net effect must be considered. There can for example be risks associated with sustainable development
18. China, as the country with the biggest yearly emission footprint, faces significant potential challenges:
Heavily reliant on coal
Installed capacity of coal not expected to peak before 2025
Energy development strategies may have a lag of up to 15 years (so, strategies put in place now may still be in effect up to 15 years in the future)
There is an over capacity of coal power plants
Coal is profitable
Coal is subsidized and protected
Industries are heavily reliant on coal
Regulations on new investment in dirty energy have been relaxed
Pollution and emission fines probably aren’t harsh enough
Renewable technology probably can’t meet the scale it needs to yet that coal currently can (part of this has to do with existing energy and electricity infrastructure and systems)
Switching from coal to renewables has short term trade-offs such as loss of jobs and disposable income
Government may lose tax income from decreased coal use
Renewables can rely on good geographic positioning, and cities in particular as the major power users may be poorly set up to receive renewable power
There’s been issues in coal to gas transitions already
Electric cars in China may currently have similar emissions to conventional combustion vehicles
Read more about potential challenges in these resources:
Future Targets For Emission Reductions
Read more in this guide about potential future targets for emission reductions.
Cost To Address Climate Change
One very rough estimate (that should be used as a very general guide only) of aggressively pursuing all low cost greenhouse gas reduction/abatement options is:
… the total global economic cost would be €200-350 billion per year by 2030. This is less than one percent of the forecasted global GDP in 2030
… if we include these additional opportunities, our maximum technical abatement potential by 2030 totals 47 billion tonnes of CO2e per year.
Our maximum global potential is therefore a 65-70% reduction relative to our current projected pathway.
Read more in this resource:
One of the latest IPCC reports has this to say on costs:
Global model pathways limiting global warming to 1.5°C are projected to involve the annual average investment needs in the energy system of around 2.4 trillion USD between 2016 and 2035 representing about 2.5% of the world GDP
Uncertainties & Challenges Related To Our Understanding & Assessment Of Climate Change
A transparent climate expert or climate scientist/researcher should admit there are still some things that we are uncertain about when it comes to knowing the full picture with climate change and global warming.
Some of these things might include:
– The limitations in using climate models in terms of what they can and can’t simulate or forecast, the assumptions and data fed into them, and how they work.
Climate models also can’t yet predict abrupt climate events
How accurately we can forecast climate change into the future (because of significant variables like global political climate policy into the future, technical barriers, economic growth, the price of fossil fuels, increases in energy and carbon efficiency, trends in the energy and transport sectors – particularly in major countries like China, human GHG emissions into the future, the behavior of the Sun into the future, short term disturbances like El Niño or volcanic eruptions, feedback processes that dampen or reinforce disturbances to the climate system like cloud formation, but also include water vapour and ice feedbacks, ocean circulation changes, and natural cycles of greenhouse gases, and so on)
– How accurately we can forecast the impact or effects of climate change in the future (on humans, the economy, different regions of the world, animals, the environment etc.) – it is freely admitted that the impact could be worse or better than predicted
– There’s no way to guarantee the emissions reporting of each country is fully accurate – ‘[there is] no sure way of independently verifying whether national governments are telling the truth about their own emissions or of knowing by how much global anthropogenic emissions are actually increasing’ (e360.yale.edu)
– Not all fossil fuels emit the same amount of GHGs, so calculating emissions can sometimes be challenging – ‘Chinese coal generally has a much lower carbon content than typical coal burned around the world. So every ton burned releases less CO2 — on average 40 percent lower than the values used in calculations by the UN’s Intergovernmental Panel on Climate Change (IPCC) (e360.yale.edu)
– To an extent, the accuracy of what we know about global temperature records from the past (pre 1850 at least), is subject to the reliability/accuracy of certain studies and estimates based on things like ancient Earth samples and human proxies.
Read more about determining and interpreting Earth’s climate history in this guide
– The exact drivers or reasons for certain behaviors in Earth’s climate and temperature history – one example of this is the 100,000 year problem, which is related to the lack of an obvious explanation for the periodicity of ice ages at roughly 100,000 years for the past million years, but not before (read more here – https://en.wikipedia.org/wiki/100,000-year_problem).
Furthermore, it’s unclear if the intensification of the ice age over the last 3 million years was due to a decline in the concentrations of greenhouse gases, or if other climate events like the thermal spikes in the PETM period were caused by methane releases.
Another example is trying to go back 1000’s of millions of years ago where ‘proposals are poorly constrained by existing experimental evidence’ … and there’s other examples of climate events where causes or factors are not well known or are unclear (read more here – https://en.wikipedia.org/wiki/Geologic_temperature_record)
– CO2 Concentrations From The Past
[there can be disputes about what] ‘atmospheric CO2 concentrations during the last 7,000–10,000 year period’ [actually were when analysing fossil leaves. Some argue according to what they analyse in the leaves, whilst others dismiss these claims citing calibration problems] (wikipedia.org).
Further to this and relevant to this dispute, ‘… is the observation that Greenland ice cores often report higher and more variable CO2 values than similar measurements in Antarctica. However, the groups responsible for such measurements (e.g. H.J. Smith et al.) believe the variations in Greenland cores result from in situ decomposition of calcium carbonate dust found in the ice’ [and low dust concentrations in Greenland cores seem to back up matching Antarctic and Greenland measurements] (wikipedia.org)
– Scientific understanding of abrupt climate change is generally poor … [and] Climate models are unable yet to predict abrupt climate change events, or most of the past abrupt climate shifts (wikipedia.org)
– The impact of natural forcings can be unpredictable over short time spans of a decade or so, which means we may not be able to see their impact until a few decades or a century in the future (one example of this is the recent El Niño which we are uncertain of how much impact it had on the climate. This also means that, at present, there is no way that atmospheric modellers will be able to verify whether one set of Paris emissions targets are working before the next set are introduced (e360.yale.edu)
– How sensitive Earth’s climate really is (climate sensitivity) to climate drivers and other variables.
When you consider that target pathways, forecasts, and cumulative emission vs expected warming estimates are based on assumptions of climate sensitivity – it’s a pretty big variable
– It’s very difficult to assess regional climate change – ‘It is very difficult to tell in detail how climate change will affect individual locations, particularly with respect to rainfall. Even if a global change were broadly known, its regional expression would depend on detailed changes in wind patterns, ocean currents, plants, and soils.’ (science.org.au)
– How exactly Earth’s feedback loop will react in the future
– Potentially inconclusive science linking El Niño or La Niña events to climate change (blogs.ei.columbia.edu)
– How rainforests and other eco systems might actually respond to climate change (‘We know remarkably little … about how much CO2 healthy growing forests, vegetation, and soils absorb or about emissions from land use changes such as deforestation … may be larger than generally assumed. Scientists don’t even agree whether, taken overall, tropical forests are a sink or a source of atmospheric CO2’ – e360.yale.edu)
– Agriculture, forestry and land use carriers uncertainty as a part of society that emits and sequesters greenhouse gas, due to factors like the standing biomass of tropical forests being uncertain, among other factors
– Linking certain events to the recent warming trend
Some events can only be linked with a % of probability, and can’t be linked with absolute certainty
– Determining what exact impact the effects of a changing climate have on humans, and attributing future impact
For example, some reports may indicate that there might be uncertainty in determining the impact of climate related events on humans, determining what deaths in the future might be attributable to climate change, and what exactly can be attributed to the use of different energy sources
– The uncertainty and limitations in calculating carbon footprints for products and services
Further resources on the uncertainty of various aspects of climate change are:
The probeinternational.org report:
[Outlines aspects of climate change that have a wide consensus but there is debate upon, aspects that are not well understood, and developments we are making with climate science]
One of the skepticalscience.com reports:
[Is a summary of the above report]
One of the royalsociety.org reports:
[Discusses how complex processes and feedbacks shape our climate, how we can’t predict future emissions, how there’s a range of scenarios for each C02 emission path, and how over the timespan of a decade or so, natural variability can modulate the effects of an underlying trend in temperature]
A ox.ac.uk report:
[Explains how climate models work and how models contain a degree of uncertainty. Also, explains how scientists are trying to quantify the amount of uncertainty in the models]
One of the royalsocietypublishing.org reports:
[Summarises how we might look to represent uncertainty in climate science, how models have uncertainty, and how there can be uncertainty in projections of climate change]
The forbes.com reports:
[Says there is uncertainty in climate modelling, but this uncertainty is sometimes used by critics to overstate the uncertainty about the possible outcomes]
The climatechangeinaustralia.gov.au report:
[Explains how we achieve confidence in climate science, where the uncertainty lies, and how scientists deal with and address uncertainty in their processes]
One of the skepticalscience.com reports:
[Outlines how to interpret some climate models and graphs, and the types of uncertainties they might have]
One of the skepticalscience.com reports:
[Outlines the uncertainty of climate sensitivity to doubling emissions from pre industrial levels]
One of the skepticalscience.com reports:
[Discusses the sensitivity of the climate to CO2 emissions]
One of the carbonbrief.org reports:
[Uncertainties that surround the revised 1.5 degrees carbon budget]
A wri.org report:
[Outlines the uncertainties to do with the carbon budget, and other climate science uncertainties]
One of the carbonbrief.org reports:
[More summaries of the uncertainties to do with carbon budgeting and overall climate science uncertainties]
Potential Disputes & Uncertainty Over Linking CO2 & Greenhouse Gas Levels To Past Climate Events
There can be disputes or uncertainty in linking CO2 and greenhouse gas levels to climate events from the past:
– Lack Of Certainty Around Greenhouse Gases Being The Primary Cause Of Abrupt Climate Events
[There is a lack of certainty around whether the release of methane from frozen ice was the primary cause of abrupt climate change events roughly 55 to 65 million years during the PETM period, where there was thought to be abrupt thermal spikes] (wikipedia.org)
– Lack Of Certainty Around CO2 Being The Primary Cause Of Intensification Of An Ice Age
The gradual intensification of [the] ice age over the last 3 million years has been associated with declining concentrations of the greenhouse gas carbon dioxide, though it remains unclear if this change is sufficiently large to have caused the changes in temperatures.
[This is because] Decreased temperatures can cause a decrease in carbon dioxide as, by Henry’s Law, carbon dioxide is more soluble in colder waters, which may account for 30ppmv of the 100ppmv decrease in carbon dioxide concentration during the last glacial maximum (wikipedia.org)
– Greenhouse Gases & The 100,000 Year Problem
There is some uncertainty around the role of impact of greenhouse gases in the 100,000 years problem (wikipedia.org)
Do These Uncertainties Disprove Climate Change Or Remove Potential Future Risk?
A common point some resources make is that just because there are some uncertainties to do with some aspects of climate change, this does not remove the potential risk that climate change may present significant risks to Earth’s future.
These uncertainties also do not conclusively disprove the current consensus climate change.
Uncertainty about the climate system does not decrease risk associated with greenhouse gas emissions, because it works in both directions: climate change could prove to be less severe than current estimates, but could also prove to be worse.
Even if future changes from greenhouse gas emissions are at the low end of the expected range, a high-emissions pathway would still be enough to take the planet to temperatures it has not seen for many millions of years
In regards to climate models:
No-one acknowledges the limitations of computer climate models more readily than modellers themselves, who will frequently bemoan the roughness of the resolution at which they have to work given the tools available.
But does this mean that we have to wait for complete certainty before acting? [No]
Climate change is complex:
Are you willing to accept the risk [of severe weather and environmental events happening]?
In such a complex system, our knowledge of many parts of the climate system is unlikely to ever be definitive.
However, it’s clearly the case that even uncertain answers can help us to work out the scale of the risks we face from climate change, and how to manage them.
Additionally, we are always making developments and advances in our ability to observe and understand climate change:
… several major issues make it impossible to give precise estimates of how global or regional temperature trends will evolve decade by decade into the future.
[But] Scientists have made major advances in the observations, theory, and modelling of Earth’s climate system; and these advances have enabled them to project future climate change with increasing confidence.
Comparing Conditions & Variables From The Past, To Earth’s Current Condition & Set Of Variables
What some people argue or point out about climate change and global warming, is that if you are trying to make a theory or conclusion on what the impact of human greenhouse emissions on the climate will be in the current time (or since warming trend started), you have to be able to prove that all of the same variables and the same conditions existed at one point in Earth’s past, and the outcomes on the climate (in the past or now) are the same, or very similar.
If this is not the case (i.e. there isn’t very solid proof of past similar circumstances, similar factors/variables, and similar outcomes to what we are seeing now), these people argue that current climate science and climate change information holds less validity.
This is obviously just one argument or opinion though.
Another Argument Or Point Made By Those Questioning The Consensus
Some who question the consensus also point out that Earth’s climate has always naturally changed, and climate changes we see now are part of the natural climate process of Earth
… Another Way To Look At Our Understanding Of Climate Change – What Is Widely Accepted, What There Is Some Debate About, & What There Is Uncertainty About Or Not Understood
This is another way at breaking down our understanding of climate change … categorising what we know for sure, what we might know, and what we don’t understand well at all.
They might be categorised unofficially into these three broad categories:
What we know for sure …
Generally, what we have observed and measured since 1850, and especially since around 1950 when more modern and accurate technology started being used to measure and analyse Earth’s climate and associated aspects of climate change
What we think we might know …
Studies about the past and future of Earth’s climate and climate related events e.g. what we can study about the Earth’s climate history from proxies and ancient Earth records
What we may have uncertainty about
The factors we have outlined above in this guide under the ‘uncertainties’ section
A couple of good resources that outline these categories well are the probeinternational.org report, and the skepticalscience.com report
Climate Change Overall Is A Complex Process – It Has Drivers, Amplifiers, Diminishers & Feedbacks That All Interact With Each Other
Climate change can be complex. One of those complexities is the feedback effect in the climate system …
CO2 does not act by itself in the environment or climate system
The climate system involves feedbacks that amplify or diminish an initial change to the system
The most important feedbacks involve various forms of water.
A warmer atmosphere generally contains more water vapour … and, water vapour is treated as an amplifier, and not a driver, of climate change.
Higher temperatures in the polar regions melt sea ice and reduce seasonal snow cover, exposing a darker ocean and land surface that can absorb more heat, causing further warming.
Another important but uncertain feedback concerns changes in clouds. Warming and increases in water vapour together may cause cloud cover to increase or decrease which can either amplify or dampen temperature change depending on the changes in the horizontal extent, altitude, and properties of clouds.
The latest assessment of the science indicates that the overall net global effect of cloud changes is likely to be to amplify warming.
The ocean moderates climate change. The ocean is a huge heat reservoir, but it is difficult to heat its full depth because warm water tends to stay near the surface. The rate at which heat is transferred to the deep ocean is therefore slow; it varies from year to year and from decade to decade, and helps to determine the pace of warming at the surface.
Observations of the sub-surface ocean are limited prior to about 1970, but since then, warming of the upper 700 m (2,300 feet) is readily apparent. There is also evidence of deeper warming.
Surface temperatures and rainfall in most regions vary greatly from the global average because of geographical location, in particular latitude and continental position.
Both the average values of temperature, rainfall, and their extremes (which generally have the largest impacts on natural systems and human infrastructure), are also strongly affected by local patterns of winds.
Estimating the effects of feedback processes, the pace of the warming, and regional climate change requires the use of mathematical models of the atmosphere, ocean, land, and ice (the cryosphere) built upon established laws of physics and the latest understanding of the physical, chemical and biological processes affecting climate, and run on powerful computers.
Models vary in their projections of how much additional warming to expect (depending on the type of model and on assumptions used in simulating certain climate processes, particularly cloud formation and ocean mixing), but all such models agree that the overall net effect of feedbacks is to amplify warming.
Responses To Some Of The Most Common Arguments Made Against Climate Change & Global Warming
Skeptical Science has resources on some of the most common arguments made against various aspects of climate change.
You can read their answers to these arguments in the skepticalscience.com ‘Arguments’ report
There’s also a resource discussing the ‘Global Warming Controversy’ at wikipedia.org
Some people who are skeptical of the consensus of climate change, or are perhaps unsure, might have some of the following points:
The climate consensus number of 97% is based on the IPCC figure, which is flawed with how they calculate it
Climate change research, reporting and funding has financial and political agendas and conflicts of interest involved with it
We’ve put together a few guides that both challenges and support the current consensus on climate change:
Can Climate Change Funding, Research & Reporting Be Trusted?
Agreeing With The Current Consensus On Climate Change (Potential Arguments Of A Supporter)
Challenging The Current Consensus On Climate Change (Potential Arguments Of A Skeptic)
Alternative Claims Made About The Climate Change Consensus
Various sources have claims which are in opposition to the consensus on climate change.
From zerohedge.com [summarising Finnish and Japanese studies]:
[there is practically no man made climate change]
[in the last hundred years, the temperature changed about] 0.1°C because of carbon dioxide. The human contribution was about 0.01°C
‘New evidence suggests that high-energy particles from space known as galactic cosmic rays affect the Earth’s climate by increasing cloud cover, causing an ‘umbrella effect’ … [this umbrella effect is a natural occurrence and could be the] prime driver of climate warming, and not man-made factors
[Scientists responsible for these findings] ‘are most concerned with the fact that current climate models driving the political side of debate, most notably the Intergovernmental Panel on Climate Change’s (IPCC) climate sensitivity scale, fail to incorporate this crucial and potentially central variable of increased cloud cover’ [and] ‘models … cannot compute correctly the natural component included in the observed global temperature. The reason is that the models fail to derive the influences of low cloud cover fraction on the global temperature’
[We at least need to] ‘rethink the impact of clouds on climate’
Thomas Sowell has spoken about several contrary points to the climate change issue, such as the rise of CO2 lagging temperature/climate rising.
Although, SkepticalScience provides feedback on this, noting how CO2 amplifies warming without having to initiate it.
Walter E Williams notes that ‘Geophysicists estimate that just three volcanic eruptions — Indonesia (1883), Alaska (1912) and Iceland (1947) — spewed more carbon dioxide and sulfur dioxide into the atmosphere than all of mankind’s activities during our entire history.’
Once again though, SkepticalScience sheds more light on volcanoes and CO2 emissions.
More Summary Guides On Climate Change
Some other useful summary guides on climate change might be found in the science.org.au (summary page), royalsociety.org (main page), and climate.nada.gov (FAQ page) resources
Other Notes On Climate Change
CO2 is strongly related to economic growth in some countries and the use of coal as an energy source
Reduced consumption, increased production efficiency, and using less carbon intensive energy sources, can both lead to overall lower carbon intensity of an activity, sector or economy
When looking at the CO2 emissions of a country, what should be asked is if those emissions include the carbon footprint in the materials, goods and services they import – direct and indirect carbon should be included in all climate change calculations to get the most accurate picture. Imports vs exports are important to consider.
Further warming might carry the risk that the Earth gets to the point where it doesn’t matter how much we reduce emissions, and natural feedback processes start to continually amplify the warming already set in motion.
Other Guides On Climate Change & Emissions
Carbon Footprint Of Common Everyday Things, Products & Foods
5. Various ‘Better Meets Reality’ guides
31. Hannah Ritchie and Max Roser (2018) – “CO₂ and other Greenhouse Gas Emissions”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions’ [Online Resource]
60. http://report.ipcc.ch/sr15/pdf/sr15_spm_final.pdf (‘Summary For Policy Makers’ IPCC Special Report)
85. IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA at http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_FINAL.pdf
114. Hannah Ritchie & Max Roser (2019) – “Energy Production & Changing Energy Sources”. Published online in OurWorldInData.org. Retrieved from https://ourworldindata.org/energy-production-and-changing-energy-sources#introduction
128. https://www.cicero.oslo.no/no/posts/klima/how-much-carbon-dioxide-can-we-emit (lists the 4 main choices someone must make in choosing a carbon budget, and the importance of negative emissions)