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Title: Why Do CO 2 Quadrupling Simulations Warm More Than Twice as Much as CO 2 Doubling Simulations in CMIP6?
Abstract We compare abrupt CO2‐quadrupling (abrupt‐4xCO2) and ‐doubling (abrupt‐2xCO2) simulations across 10 CMIP6 models. Two models (CESM2 and MRI‐ESM2‐0) warm substantially more than twice as much under abrupt‐4xCO2 than abrupt‐2xCO2, which cannot be explained by the non‐logarithmic scaling of CO2forcing. Using an energy balance model, we show that increased warming rates within these two models are driven by both less‐negative radiative feedbacks and smaller global effective heat capacity under abrupt‐4xCO2. These differences are caused by a decrease in low cloud cover andshallower ocean heat storage, respectively; both are linked to smaller fractional declines in the Atlantic Meridional Overturning Circulation (AMOC) under abrupt‐4xCO2 (relative to abrupt‐2xCO2). On a global scale, higher climate sensitivity under larger forcing can be explained by a feedback‐temperature dependence; however, we find that forcing‐dependent spatial warming patterns due to AMOC decline are an important physical mechanism which reduces warming in a way that is not captured by a global‐mean framework.  more » « less
Award ID(s):
1752796
PAR ID:
10515884
Author(s) / Creator(s):
; ;
Publisher / Repository:
Geophysical Research Letters
Date Published:
Journal Name:
Geophysical Research Letters
Volume:
51
Issue:
10
ISSN:
0094-8276
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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