What Earth’s Climate Was Like In The Past (Earth Climate History Timeline)

A common statement by people about climate change is that the ‘Earth’s climate has changed before’.

In this guide, we look at the Earth’s climate history timeline of the last century, through to billions of years ago.

We also look at how warm the Earth’s climate might have got in the past.


Summary – What Earth’s Climate History Timeline Might Have Looked Like

The Earth is roughly 4.5 billion years old

It has has gone through different patterns of temperature and climate changes throughout different time periods in it’s history

Recent temperature and climate records (from 1850 to present) are obtained from more modern technology such as thermometers, and satellites and balloons

Prior to that, different forms of ancient Earth samples (ice cores, deep sea sediments, tree rings, and so on) are used along with fields of study like Paleoclimatology to reconstruct, estimate or approximate what more ancient climates and temperatures were like. 

There can be some level of uncertainty with using ancient Earth data to interpret climate history, and this might be especially true the further back in time we go.

Climate history from millions, or hundreds of millions of years ago (and further back) for example might be seen as approximations, or have other issues with determining specific or absolute conclusions from (we have listed some of the uncertainties or issues with determining ancient Earth climate and temperature in the guide below)

Earth’s climate history can be divided into unofficial major time periods …

1850 To Now

Globally averaged near-surface air temperature (global average temperature) rose by around 0.8°C between 1850 and 2012.

This rate of warming is much quicker than any warming thought to have happened in the past 20,000 years or so


From 20,000 BC (The Last 20,000 Years Or So)

Earth’s climate has been unusually stable, but overall, has gradually been incrementally warming since that time (when it came directly out of an ice age at about -4.3 degrees celsius)


3 Million Years Ago 

The last 3 million years have been characterized by cycles of glacials (colder periods) and interglacials (warmer periods) that are part of a deepening phase within a prolonged ice age.

Some sources indicate ‘Earth’s globally averaged surface temperature has risen and fallen by about 5˚C in ice-age cycles, roughly every 100,000 years or so, over the last 1 million years … and these changes have happened gradually’

[Going back more than 1 to 3 million years ago is when it is estimated that temperatures or CO2 levels were higher than today … and it’s the rate of warming in modern times that is the concern compared to how fast the Earth has generally warmed in the past]


40 Million Years Ago

A more extended ice age began about 40 million years ago with the glaciation of Antarctica (and eventually fed into the peak of the ice age at 20,000 BC).


About 65 Million Years Ago

There was a series of abrupt thermal spikes that lasted no more than a few hundred thousand years (thought to have been caused by the release of methane and frozen methane ice)


66 to 100 Million Years Ago 

Average global temperatures are thought to have reached some of their highest in the last 200 million years


542 Million Years Ago 

Temperatures could fluctuate in this time


1000 Million Years Ago 

There could have been two or more major glaciations


Prior To 1000 Million Years Ago

‘evidence of temperature changes and glaciation is usually too scattered and sporadic to draw firm conclusions though it seems likely that temperature fluctuations were also substantial during this period’ (wikipedia.org)

It’s thought that several ‘Abrupt climate change events’ also happened throughout Earth’s history and in and around these periods


*It’s worth noting, for various reasons, the further back we try to estimate or determine Earth’s climate or temperature (say 10’s of millions or 100’s of million of years ago, and further back), the more approximate these determinations or estimates might become, and they are perhaps best viewed as a qualitative indication only in some instances.

It’s also worth noting that these climate estimates are global, and not regional. Regional climates can differ from the overall global average climate.


How Much Has Earth’s Climate & Temperature Warmed Recently (Since Around 1850)?

The change in global surface temperature [up to 2019], relative to 1951-1980 average temperatures, is 0.9 degrees celsius (climate.nasa.gov)

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 (science.org.au)

Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade (earthobservatory.nasa.gov)

The 10 warmest years on record [since 1880] have all occurred since 1998, and 9 of the 10 have occurred since 2005 (climate.gov)


The sciencealert.com link in this guide shows on it’s infographic how temperature spikes in the 20th century and around 1950/60 when the industrial revolution hits.

This coincides with a large increase of fossil fuel based greenhouse gas emissions from human activities.


What Is Significant About The Recent Warming Trend Since About 1850?

While there have been past periods in Earth’s history when temperatures were warmer than they are now, the rate of change that is currently taking place is faster than most of the climate shifts that have occurred in the past, and therefore it will likely be more difficult to adapt to. 

– climatecentral.org


Earth’s Climate Since 20,000 BC (Roughly The Last 22,000 Years)

Sciencealert.com has an infographic going back the last 22,000 years:

In 20,000 BCE, Earth was at the peak of the last ice age, and was 4.3 degrees Celsius colder than it was in the late 20th century.

Slight changes in Earth’s orbit at around 18500 BCE meant some of that polar ice could finally be reached by more sunlight, and the warming period began

There’s been a gradual and relatively predictable heating since that time, mixed in with some temporary periods of cooling. The climate has been remarkably stable for the past 12,000 years

Between 9000 and 8500 BCE … temperatures hit modern levels, and continued to rise

In the 21st century, and particularly around and after the industrial revolution, CO2 levels increased and the rate of temperature increase has been much quicker than at any time in the past 22,000 years

View the infographic by sciencealert.com here of Earth’s climate since 20,000 BCE


Over the last few thousand years [of the last 20,000 year period] during which civilisations developed, climate was unusually stable.

The last 8,000 years, which includes most recorded human history, have been relatively stable at the warmer end of this temperature range. 

– science.org.au


Earth’s Climate The Last 800,000 To 1 Million Years

Science.org.au has a graph showing the last 800,000 years of globally averaged surface temperature

What we see is ‘Over the past million years, Earth’s globally averaged surface temperature has risen and fallen by about 5˚C in ice-age cycles, roughly every 100,000 years or so … [and] Most past changes in global temperature occurred slowly, over tens of thousands or millions of years’


The record of the distant past (millions of years) tells us that climate has varied greatly through Earth’s history.

It has, for example, gone through ten major ice age cycles over approximately the past million years.

– science.org.au


The Earth’s climate has changed throughout history.

Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. 

– climate.nasa.gov


Earth’s Climate Millions Of Years Ago & Beyond

These three sources have various images which attempt to reconstruct or estimate Earth’s temperatures and climate at various periods going up to hundreds of millions of years back:

Earth’s Global Temperature Record (wikipedia.org)

Earth’s Geologic Temperature Record (wikipedia.org)

Earth’s Global Average Surface Temperature (wikipedia.org)


Earth’s climate has changed dramatically many times since the planet was formed 4.5 billion years ago. 

– science.org.au


Prior to 5 million or 100 million years ago, we are making more of a qualitative, more approximate (and not as accurate) guess about climate patterns.

Evidence of temperature changes and glaciation is usually too scattered and sporadic to draw firm conclusions – though it seems likely that temperature fluctuations were also substantial [and temperatures could have been much higher than today]

– wikipedia.org


Several million years ago … global average temperature was a few degrees higher than today and warm, tropical waters reached much farther from the equator, resulting in very different patterns of ocean and atmospheric circulation from today.

Most past changes in global temperature occurred slowly, over tens of thousands or millions of years.

However, there is also evidence that some abrupt changes occurred, at least at regional scales. 

– science.org.au


… around 3 million years ago … Arctic temperatures were 11 to 16°C warmer … Global temperatures over this period is estimated to be 3 to 4°C warmer than pre-industrial temperatures. 

– skepticalscience.com


The last time there was this much carbon dioxide (CO2) in the Earth’s atmosphere, modern humans didn’t exist.

Mega toothed sharks prowled the oceans, the world’s seas were up to 100 feet higher than they are today, and the global average surface temperature was up to 11°F warmer than it is now.

[it is estimated that] 10 to 15 million years ago temperatures were substantially warmer than they are now [and, humans didn’t exist at this point in time]

While there have been past periods in Earth’s history when temperatures were warmer than they are now, the rate of change that is currently taking place is faster than most of the climate shifts that have occurred in the past, and therefore it will likely be more difficult to adapt to. 

– climatecentral.org


How Warm Did The Climate & Temperatures Get Throughout Earth’s History?

Some of the warmest periods in Earth’s history might have been:

About 65 million years ago – During the PETM [period], the global mean temperature seems to have risen by as much as 5-8 °C (9-14 °F) to an average temperature as high as 23 °C (73 °F), in contrast to the global average temperature of today at just under 15 °C (60 °F).

– wikipedia.org


About 66 to 100 million years ago – During the later portion of the Cretaceous … average global temperatures reached their highest level during the last ~200 million years.

– wikipedia.org


About 100 million to 542 million years ago – a period of fluctuating temperature between ice ages, such as the current age, and “climate optima”, similar to what occurred in the Cretaceous.

Roughly 4 such cycles have occurred during this time with an approximately 140 million year separation between climate optima.

– wikipedia.org


Quick/Rapid Warming – Changes recorded in the climate of Greenland at the end of the Younger Dryas, as measured by ice-cores, imply a sudden warming of +10 °C (+18 °F) within a timescale of a few years. 

Other abrupt changes are the +4 °C (+7.2 °F) on Greenland 11,270 years ago or the abrupt +6 °C (11 °F) warming 22,000 years ago on Antarctica.

– wikipedia.org


Abrupt Climate Change Events

Read more in this guide about Abrupt Climate Change Events.

Something interesting to note about abrupt climate change, as noted by some sources:

Scientific understanding of abrupt climate change is generally poor (wikipedia.org)


How Do We Determine Or Estimate Earth’s Climate & Temperature From The Past?

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.

These are direct measurements of the temperature and climate.

Prior to 1850, temperatures have either been estimated, or studied (with Paleoclimatology) i.e. direct measurements are not available, and we rely on proxies, ancient Earth material and these studies and reconstructions instead.

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 deep sea sediment cores]

Read more about these time periods and methodologies and data used to understand global temperature record here (wikipedia.org)


The Reliability, Accuracy & Uncertainty Associated With Determining Earth’s Climate & Temperature History

Since 1850, more modern technology (thermometers, and then more recently satellites and balloons) has been used to measure and collect data on Earth’s global temperature and climate.

Going back further in time, we rely on Paleoclimatology studies, and analysis of ancient or very old Earth material like tree rings, ice cores, and deep sea sediments (geological records).

There’s a differences in detail between these two time periods:

‘The most detailed information [on global temperatures] exists since 1850, when methodical thermometer-based records began [and older information on temperatures and climate relies on] numerous estimates of temperatures since the end of the Pleistocene glaciation, particularly during the current Holocene epoch. Older time periods are studied by paleoclimatology.’ (wikipedia.org)


There can be some other issues with interpreting Earth’s climate the further back in time we go. Some of those issues might include:

With Geologic temperature records (such as deep sea sediments), 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).

When determining global temperature records from 800,000 years ago with ice cores –  ‘large-scale signals from the cores are clear, [but] there are problems interpreting the detail, and connecting the isotopic variation to the temperature signal’ (wikipedia.org). 

There can be a ‘discrepancy between the reconstructed geologic temperature record and the reconstructed amount of incoming solar radiation, or insolation over the past 800,000 years’ (wikipedia.org)

The ‘Direct combination of [some] interpreted geological temperature records [are] not necessarily valid, nor is their combination with other more recent temperature records, which may use different definitions … [Instead, they may be used for] an overall perspective … even when imprecise’ (wikipedia.org)

Temperatures on Earth going back 10’s or 100’s of million of years back and more may be ‘very approximate, and best viewed as a qualitative indication only’ (wikipedia.org)

Determining Earth’s climate or temperatures 1000’s of millions of years ago or billions of years ago may have ‘proposals [that] are poorly constrained by existing experimental evidence’ (wikipedia.org)

Proxy vs observational records of Earth’s climate history – ‘Even the best proxy records contain far fewer observations than the worst periods of the observational record, and the spatial and temporal resolution of the resulting reconstructions is correspondingly coarse’ (wikipedia.org)

Natural, Numerical Data vs Human Temperature Data – ‘[human] records can be used to infer historical temperatures, but generally in a more qualitative manner than natural proxies’ (wikipedia.org)

‘A substantial achievement of the last 30 years of climate science has been the production of a large set of actual measurements of temperature history (from physical proxies), replacing much of the earlier geological induction (i.e. informed guesses) … Because many proxy temperature reconstructions indicate local, not global, temperature — or ocean, not air, temperature – substantial approximation may be involved in deriving these global temperature estimates’ (wikipedia.org)

‘Temperature estimates from oxygen isotope measurements on the north Greenland ice core … [can yield slightly different interpretations of temperatures depending on if simple procedures or more modern and complex procedures are used]’ (wikipedia.org)

With Paleoclimatology – ‘the deep marine record, the source of most isotopic data, exists only on oceanic plates, which are eventually subducted: the oldest remaining material is 200 million years old. Older sediments are also more prone to corruption by diagenesis. Resolution and confidence in the data decrease over time.’ (wikipedia.org)

Scientific understanding of abrupt climate change is generally poor (wikipedia.org)


Factors That Impact & Drive Earth’s Climate At Any One Time

You can read more in this guide about the factors that influence a change in the Earth’s climate.



1. https://en.wikipedia.org/wiki/Geologic_temperature_record

2. https://en.wikipedia.org/wiki/Global_temperature_record

3. https://en.wikipedia.org/wiki/File:All_palaeotemps.png#Summary

4. https://en.wikipedia.org/wiki/Paleoclimatology

5. https://www.climatecentral.org/news/the-last-time-co2-was-this-high-humans-didnt-exist-15938

6. https://climate.nasa.gov/vital-signs/global-temperature/

7. https://www.science.org.au/learning/general-audience/science-climate-change/2-how-has-climate-changed

8. https://earthobservatory.nasa.gov/world-of-change/DecadalTemp

9. https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature

10. https://www.sciencealert.com/why-4-5-million-years-of-fluctuating-global-temperatures-can-t-explain-climate-change-today

11. https://en.wikipedia.org/wiki/Abrupt_climate_change

12. https://www.bettermeetsreality.com/how-fast-did-earths-climate-change-in-the-past-abrupt-climate-change-events/

13. https://skepticalscience.com/climate-change-little-ice-age-medieval-warm-period-intermediate.htm

14. https://en.wikipedia.org/wiki/100,000-year_problem

15. https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere#Measuring_ancient-Earth_carbon_dioxide_concentration

16. https://www.bettermeetsreality.com/our-most-complete-updated-guide-on-climate-change-global-warming/

17. https://climate.nasa.gov/evidence/

18. https://www.science.org.au/learning/general-audience/science-booklets/science-climate-change/summary

19. https://www.skepticalscience.com/print.php?r=77

20. https://www.bettermeetsreality.com/how-fast-did-earths-climate-change-in-the-past-abrupt-climate-change-events/

Leave a Comment