Reconstructions of past temperatures show much colder periods with higher CO2 levels or as-warm or warmer periods with much lower CO2 levels.
A new study (Paus, 2020) indicates modern July temperatures center around 7.5 to 8°C in the Scandes Mountains (Norway). Today’s CO2 atmospheric concentration has reached 410 ppm.
During the latter stages of the last ice age (19,000 to 17,000 years ago), Late Glacial (LG) CO2 fluttered near 200 ppm. But with the discovery of temperature-sensitive tree species in the area it can be affirmed that July temperatures were also “at least 7-8°C” in the Scandes at this time. Despite more than a doubling of CO2, there has been no consequent summer temperature increase in this remote location.
Image Source: Paus, 2020
In another new study from Eastern Europe, Blagoveshchenskaya (2020) has determined January temperatures were almost 11°C warmer than the Little Ice Age (700 to 300 yrs ago) and 4°C warmer than today from about 6,000 to 4,500 years ago.
CO2 levels were 270 ppm when this region was 11°C warmer and 275 ppm when 11°C colder. It is 4°C colder today, at 410 ppm, than it was when CO2 was 270 ppm.
So, once again, reconstructions of Holocene temperatures do not support the narrative that CO2 and temperature changes are correlated.