TY  - JOUR
A1  - Ring, S. J.
A1  - Mutz, S. G.
A1  - Ehlers, T. A.
T1  - Cenozoic Proxy Constraints on Earth System Sensitivity to Greenhouse Gases
Y1  - 2022-12-08
VL  - 37
IS  - 12
JF  - Paleoceanography and Paleoclimatology
DO  - 10.1029/2021PA004364
PB  - 
N2  - The long‐term extent of the Earth system response to anthropogenic interference remains uncertain. However, the geologic record offers insights into this problem as Earth has previously cycled between warm and cold intervals during the Phanerozoic. We present an updated compilation of surface temperature proxies for several key time intervals to reconstruct global temperature changes during the Cenozoic. Our data synthesis indicates that Earth’s surface slowly cooled by ca. 9°C during the early Paleogene to late Neogene and that continent‐scale ice sheets developed after global temperature dropped to less than 10°C above preindustrial conditions. Slow cooling contrasts with the steep decrease in combined radiative forcing from past CO<sub>2</sub> concentrations, solar luminosity, and ocean area, which was close to preindustrial levels even as Earth remained in a much warmer state. From this, we infer that the Earth system was less sensitive to greenhouse gas forcing for most of the Cenozoic and that sensitivity must have increased by at least a factor of 2 during the Plio‐Pleistocene. Our results imply that slow feedbacks will raise global surface temperatures by more than 3°C in the coming millennia, even if anthropogenic forcing is stabilized at the present‐day value (2 W/m<sup>2</sup>), and that their impact will diminish with further warming.
N2  - Plain Language Summary: It is not well known how much Earth’s surface temperature will change over the next few millennia as a result of increasing atmospheric CO<sub>2</sub> concentrations. This is because we still have a limited understanding of many slow climate feedback mechanisms activated by climate change that will become important in the future. Most climate models project eventual global warming of 3–4°C for doubled CO<sub>2</sub> concentration but exclude many slow climate feedbacks, such as shrinking ice sheets. The distant (geologic) past provides additional clues about the future because the climate system and all of its feedbacks were in equilibrium with naturally elevated CO<sub>2</sub>. Using up‐to‐date geologic information of the last 50 million years, we find that Earth’s climate history is best described by a switch from a moderate sensitivity, close to that found in climate models, to a much higher sensitivity in the last 3 million years. If Earth behaves the same way today as it has done in the past, melting ice sheets, natural aerosols, and shifting vegetation patterns will slowly continue to raise global warming above the 2°C target during the next few thousand years even if the human contribution does not increase any further.
N2  - Key Points: Large compilation of Cenozoic paleoclimate proxies was analyzed. Paleogene and Neogene were dominated by Earth system sensitivity of 4°C but sensitivity must have increased in the Plio‐Pleistocene. High Earth system sensitivity stresses the importance of climate change mitigation over adaptation.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/11166
ER  -