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Warming from the Last Glacial Period to the Present

It took the planet at least 7,000 years to warm by 7 °C from the last glacial period. It took only the last 100 years to warm by 1.3 °C.

Warming from the Last Glacial Period to the Present

Some argue that the climate has always been changing. The climate has indeed always changed – but the rate of current warming is unprecedented in the context of human civilization. It is the speed of change that matters for ecosystems and societies.

In the long geological timescale of Earth’s history, it is possible to find periods in which the climate was much colder than today (glacial periods of ice ages) as well as much warmer (e.g. the age of dinosaurs). However, climate changes were always relatively slow.

From this historical perspective, the temperature change in the last hundred years shown in the graph is huge and abrupt – such a trend is not natural for the world’s climate.

Calculations and computer simulations also show that at the end of this century the planet will be about 1.5–3.5 °C warmer than in pre-industrial era, depending on how quickly greenhouse gas emissions are reduced1 (see also: Projections of Warming in 2100).

What does the temperature change mean for humans and for the living world?

During the Last Glacial Maximum (peaking between 26,000 and 20,000 years ago), Canada and northern Europe were covered by vast ice sheets, and cold tundra stretched all the way down to the Mediterranean coast. Ice sheets locked up huge quantities of water so global ocean levels were about 120 meters lower than today.

In the following ten thousand years, temperatures rose slowly and the world became 7 °C warmer.2 Glaciers melted away and the natural world adapted to this change – including humans who could now settle in previously uninhabitable northern areas. This warming period was followed by a long era in which the annual global temperature did not change very much, which was favourable for civilization growth.

Current warming,3 however, is at least 10 times faster and does not give ecosystems and species sufficient time to adapt. This abrupt warming may have far-reaching consequences for life on the planet as well as for human civilization (see also: climate tipping points and The Thresholds of Climate Tipping Risks).

How do scientists measure past temperatures?

Air temperatures have been reliably measured since the 18th century. Temperatures in earlier or even pre-historic times can be calculated based on some natural processes affected by temperature changes. One example is dendrochronology – the dating of tree rings. When a piece of wood is found by archaeologists as a part of their excavations, the growth rings allow scientists to estimate temperatures in the period when the tree was growing.

Another method studies pollen grains found at bottoms of lakes – this pollen provides useful information about plants growing by the lake in the past and researchers can thus estimate the temperatures in those times.4

Key data about past temperatures comes from the isotope analysis of marine sediments. In water (H₂O), oxygen exists as different isotopes (¹⁶O and ¹⁸O), the ratio of which changes depending on the planet’s climate. By analysing the calcium carbonate shells (CaCO₃) of dead organisms from the seafloor, scientists can determine the composition of ancient seawater and from that, reconstruct temperatures with reasonable accuracy even in the distant past.

Footnotes

  1. The value of 3.5 °C comes as the upper range of warming in the 2080–2100 period in IPCC’s SSP2-4.5 scenario. This “Middle of the Road” scenario supposes slow progress toward sustainability with greenhouse gas emissions peaking between 2040 and 2050 and then steadily declining. It is by no means the worst case scenario – if emissions continue to rise throughout the 21st century, the warming might be even bigger. See Cross-Section Box TS.1, Table 1 in Intergovernmental Panel on Climate Change. (2021). Technical Summary. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to AR6. DOI: 10.1017/9781009157896.002. ↩

  2. The dataset comes from Osman, M.B., Tierney, J.E., Zhu, J. et al. (2021). Globally resolved surface temperatures since the Last Glacial Maximum. Nature 599, 239-244. DOI: 10.1038/s41586-021-03984-4. ↩

  3. Dataset comes from NASA Goddard Institute for Space Studies, The GISS Surface Temperature Analysis version 4 (GISTEMP v4). Dataset accessed 2026-01-22. ↩

  4. Chevalier, M., et al. (2020). Pollen-based climate reconstruction techniques for late Quaternary studies. Earth-Science Reviews, 210, 103384. DOI: 10.1016/j.earscirev.2020.103384. ↩