The Global‐Mean Precipitation Response to CO2‐Induced Warming in CMIP6 Models. Issue 17 (7th September 2020)

• Record Type: Journal Article
• Authors: Pendergrass, A. G.
• Is Part Of: Geophysical research letters. Volume 47:Issue 17(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-07
• Subjects: precipitation -- climate sensitivity -- CMIP -- climate models -- emergent constraints -- climate change; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL089964
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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. 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. Plain Language Summary: The most recent generation of climate models has a higher climate sensitivity than earlier generations. A previous study argued that climate sensitivity should be related to changes in globally averaged precipitation (which is mostly made up of rainfall), so we revisit it in the new set of models. We find that compared to the previous generation of simulations, the multi‐model average rate of change of rainfall has decreased slightly, but that this change is small compared to the change in climate sensitivity and also compared to a previously proposed estimate of the rate of rainfall change that was intended to make it more consistent with currently observable aspects of climate. Finally, we look at the relationship across models between climate sensitivity and rainfall change. Like in the previous generation of models, low clouds change in a way that could influence both climate sensitivity and rainfall change, and yet climate sensitivity and rainfall change do not vary together. We show that this is because the effects of low clouds are present, but they are not the most important factor for rainfall change. Key Points: The hydrologic sensitivity (HS) in CMIP6 is 2.5% K −1 in the multi‐model mean, with a range across models of 2.1–3.1% K −1 Observationally constraining HS with the clear‐sky SW sensitivity to water vapor, as previously proposed, decreases this to 2.4% K −1 The lack of relationship between surface LW cloud effects and HS is a gap in the chain linking HS and climate sensitivity via low clouds