Climate feedbacks derived from spatial gradients in recent climatology

Abstract

Climate feedbacks, including Planck, surface albedo, water vapor-lapse rate (WVLR) and cloud feedbacks, determine how much surface temperatures will eventually warm to balance anthropogenic radiative forcing. Climate feedbacks remain difficult to constrain directly from temporal variation in observed surface warming and radiation budgets due to the pattern effect and low signal-to-noise ratio, with only order 1°C historic rise in surface temperatures and high uncertainty in aerosol radiative forcing. This study presents a new method to analyze climate feedbacks from observations by empirically fitting simplified reduced-physics relations for outgoing radiation at the top of the atmosphere (TOA) to observed spatial variation in climate properties and radiation budgets. Spatial variations in TOA outgoing radiation are dominated by the dependence on surface temperature: around 91% of the spatial variation in clear sky albedo, and 77% of spatial variation in clear sky TOA outgoing longwave radiation, is functionally explained by variation in surface temperatures. These simplified and observationally constrained relations are then differentiated with respect to spatial contrasts in surface temperature to reveal the Planck, fixed-cloud albedo (λ_albedo) and WVLR (λ_WVLR) climate feedbacks spatially for both clear sky and all sky conditions. The resulting global all sky climate feedback values are λ_WVLR=1.28 (1.13 to 1.45 at 66%) Wm-2K-1, and λ_albedo=0.64 (0.53 to 0.74) Wm-2 for the 2003-2023 period reducing to 0.35 (0.29 to 0.41) Wm-2K-1 under 4°C warming after cryosphere retreat. Our findings agree well with complex Earth system model evaluations based on temporal climate perturbations, and our approach is complementary.

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ORCID for Philip Goodwin: orcid.org/0000-0002-2575-8948

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