Tree Trunk Conundrum
Image Source: Ganyushkin et al., 2018
Between 60 and 40 thousand years ago, during the middle of the last glacial, atmospheric CO2 levels hovered around 200 ppm – half of today’s concentration.
Tree remains dated to this period have been discovered 600-700 meters atop the modern treeline in the Russian Altai mountains. This suggests surface air temperatures were between 2°C and 3°C warmer than today during this glacial period.
Tree trunks dating to the Early Holocene (between 10.6 and 6.2 thousand years ago) have been found about 350 meters higher than the modern treeline edge. This suggests summer temperatures were between 2°C and 2.5°C warmer than today during the Early Holocene, when CO2 concentrations ranged between about 250 and 270 ppm.
None of this paleoclimate treeline or temperature evidence correlates with a CO2-driven climate.
“Samples of wood having an age of 10.6–6.2 cal ka BP were [the Early Holocene] found about 350 m higher than the present treeline. It seems that the summer temperature was 2.0–2.5 °C higher and annual precipitation was double that of the present-day.”
“Buried wood trunks by a glacier gave ages between 60 and 28 cal ka BP and were found 600–700 m higher than the present upper treeline. This evidences a distinctly elevated treeline during MIS 3a and c. With a correction for tectonics we reconstructed the summer warming to have been between 2.1 and 3.0 °C [higher than today].”