No apparent state-dependency of equilibrium climate sensitivity between the Pleistocene glacial and interglacial...

Quantifying climate sensitivity is essential for future climate projections, yet it varies with major Earth system changes. We present a glacial CO₂ reconstruction using paleosols from the Chinese Loess Plateau, covering 2580 to 800 thousand years ago. A stepwise decline in glacial CO₂ levels from ~300 ppm to <200 ppm is observed. Our paleosol-based CO₂ estimates support the key role of atmospheric CO₂ in driving major climate transitions during the Pleistocene, such as the long-term global cooling and the amplification of the glacial cycles. Based on compiled glacial and interglacial CO₂ records, Earth system sensitivity, defined as the global temperature change for a doubling of CO₂ once the whole Earth system has reached equilibrium, is estimated to be ~6.2-7.4 K (3.2-12.0 K, 95% confidence). Equilibrium climate sensitivity, after accounting for the different efficacy between ice-sheet and CO₂ forcing and other slow feedbacks, is estimated to be 3.3 K (2.1-6.3 K, 95% confidence) and 3.7 K (1.7-6.3 K, 95% confidence), respectively. The lack of a significant difference between these values suggests no apparent state-dependency of climate sensitivity between glacial and interglacial climate states.