Constraining Climate Model Projections of 21st-Century Global and Regional Warming
Date
2023-04-11
Authors
Liang, Yongxiao
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Abstract
Different climate models predict different amounts of future warming over the 21st century. Such uncertainty of future warming projections can be narrowed down by emergent constraints identified based on the relationships between projected warming across climate models and observable features of simulated past climate or climate change.
For global means of projected 21st-century warming, using the observed historical global mean near-surface air temperature (GSAT) trend as a constraint results in a relatively low warming relative to unconstrained projections. Using climatological cloud metrics, robust historical predictors with reduced influence of internal variability, to constrain future warming produces a relatively high warming. Such different ranges of constrained projections can be likely explained by the influence of internal variability in the constraint. By removing the unforced internal variability in historical GSAT trends, this study identifies a relatively higher 21st-century warming range than a constrained projection based on the raw GSAT trend, and brings GSAT trend constrained projections into much closer agreement with projections constrained using climatological cloud metrics. Regarding regional constraint of projected 21st-century warming, this study demonstrates the skill of global metrics relative to regional ones, and justifies the climatology cloud metrics alone can robustly constrain regional warming over extratropical Northern Hemisphere.