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Observed and CMIP6 Modeled Internal Variability Feedbacks and Their Relation to Forced Climate Feedbacks
Inter model variations in global temperature response to increasing atmospheric carbon dioxide stem mostly from uncertainties in modeled climate feedbacks. To study potential reductions in model feedback uncertainties, we estimate observed feedbacks in response to internal variability using changes...
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Published in: | Geophysical research letters 2022-12, Vol.49 (24), p.n/a |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Inter model variations in global temperature response to increasing atmospheric carbon dioxide stem mostly from uncertainties in modeled climate feedbacks. To study potential reductions in model feedback uncertainties, we estimate observed feedbacks in response to internal variability using changes in Top Of the Atmosphere energy balance with temperature. We compare those observations with internal variability feedbacks from historical simulations of coupled and atmosphere‐only experiments from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) to identify that simulated feedbacks exhibit biases in the tropics, subtropics, and the Southern Ocean. Furthermore, we find a relation between simulated longwave and shortwave internal variability feedbacks and those where atmospheric carbon dioxide is abruptly quadrupled. In the model range of internal variability feedbacks, the observations are more consistent with moderately negative longwave feedback, and weak shortwave feedback, but the observations can't be used to rule out any models or their long‐term feedback.
Plain Language Summary
We investigate how Earth's radiation balance changes during natural variations of temperature, comparing satellite observations to global climate models. Around the globe, we find predominant negative radiative feedbacks, that is, that the temperature perturbation is dampened by the longwave radiation emitted from Earth, as well as positive feedbacks from reduced reflected of sunlight during warmer periods. The magnitudes of feedback vary across latitudes, particularly in the tropics and subtropics, something which we can relate mostly to clouds. When compared to observations, models in the latest generation as a group continue to misrepresent the negative longwave feedbacks in the tropics, subtropics, and the shortwave feedback in the Southern Ocean, although a few of the new models now match the observed. Moreover, we show that the shortwave and longwave internal variability feedbacks are related to the long‐term feedback to increasing carbon dioxide. Among the models, some underestimate and some overestimate the negative longwave feedback range indicated by observations. In the shortwave, the observational range is less consistent with the strongest positive and strongest negative model estimates.
Key Points
Observed internal variability feedback is driven by clouds in the tropics, and dominated by clear‐sky in the extratropics
Most models underestimate the |
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ISSN: | 0094-8276 1944-8007 1944-8007 |
DOI: | 10.1029/2022GL100075 |