Abstract
AbstractWe examine the response of globally averaged precipitation to global warming—the hydrologic sensitivity (HS)—in the Coupled Model Intercomparison Project phase 6 (CMIP6) multi‐model ensemble. Multi‐model mean HS is 2.5% K−1 (ranging from 2.1–3.1% K−1 across models), a modest decrease compared to CMIP5 (where it was 2.6% K−1). This new set of simulations is used as an out‐of‐sample test for observational constraints on HS proposed based on CMIP5. The constraint based on clear‐sky shortwave absorption sensitivity to water vapor has weakened, and it is argued that a proposed constraint based on surface low cloud longwave radiative effects does not apply to HS. Finally, while a previously proposed mechanism connecting HS and climate sensitivity via low clouds is present in the CMIP6 ensemble, it is not an important factor for variations in HS. This explains why HS is uncorrelated with climate sensitivity across the CMIP5 and CMIP6 ensembles.
Highlights
A new generation of climate model simulations presents an opportunity to revisit previously identified findings
We examine the response of globally averaged precipitation to global warming—the hydrologic sensitivity (HS)—in the Coupled Model Intercomparison Project phase 6 (CMIP6) multi‐model ensemble
The change in HS from CMIP5 to CMIP6 is small compared to the changes indicated by observational constraints identified in CMIP5, which reduced HS by 10% for the clear‐sky SW absorption constraint and by 30% when combined with a second constraint based on longwave cloud radiative effect (LWcre)
Summary
A new generation of climate model simulations presents an opportunity to revisit previously identified findings. One difference of the Coupled Model Intercomparison Project phase 6 (CMIP6) from previous generations is climate sensitivity, which, on average, is higher than in CMIP5 (Forster et al, 2019). Equilibrium climate sensitivity (ECS; the equilibrium surface temperature response to doubling atmospheric CO2 concentration) increased on average from CMIP5 to CMIP6, with many more models above the assessed 4.5°C upper bound of the likely range (Collins et al, 2013). On long enough time scales, precipitation and its changes are balanced by the other energy fluxes between the surface, atmosphere, and TOA. This raises the question of whether there is a change in the global‐mean precipitation response from CMIP5 to CMIP6
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