From 14,000 to 45,000 years ago, when the atmospheric CO2 values were said to be under 200 ppm, California lakes record millennial-scale mean annual air temperature (MAAT) variations of over 12°C and intervals when it was nearly 4°C warmer than modern.
Per a new paleotemperature reconstruction (Olson et al., 2023) from a California lake, there were periods during the last glacial when MAATs were both significantly colder (11.8°C) and warmer (23.9°C) than today (20.1°C).
The Holocene, ~250-275 ppm CO2, has also had periods when paleotemperatures were multiple degrees warmer than modern.
Image Source: Olson et al., 2023
Another California paleotemperature reconstruction (Feakins et al., 2019) also indicates the last glacial had abrupt warm-up periods reaching 10-15°C and MAATs ranging up to 4 to 5°C warmer than today (18°C vs. 22-23°C) between 31,000 and 24,000 years ago.
Image Source: Feakins et al., 2019
These temperature reconstructions do not support the contention that atmospheric CO2 concentrations are a driver of climate variations.
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