The question how much it was colder on earth during the last Ice Age is being re-opened. This question has preoccupied climate scientists for decades. Earlier estimates assumed that the mean global temperature during the last Glacial maximum (LGM) was around 4°C below today’s value. However, the data available for high latitudes (areas close to poles) was much better than data from the tropics and in the subtropics.

In a recently published article in Nature, new measurements of noble gases in fossil groundwater were evaluated. This finally made it possible to reconstruct temperatures in areas close to the equator in a more reliable way. The result: During LGM it was almost 6°C colder globally, so the mean temperature of the earth was 8° instead of the modern 14°C.

This new, lower value of the average temperature suggests a higher sensitivity of the temperature in relation to the CO₂ content than previously thought. This is bad news for global warming, which could therefore be more severe than previously thought.

References:

• CLIMAP, 1981.  Seasonal reconstructions  of the  Earths  surface at  the  last glacial maximum.  Map series, technical  report  mc-36, Geological Society of America.
• Seltzer, A.M., Ng, J., Aeschbach, W. et al. Widespread six degrees Celsius cooling on land during the Last Glacial Maximum. Nature 593, 228–232 (2021). https://doi.org/10.1038/s41586-021-03467-6