Solar cycle as a distinct line of evidence constraining Earth’s transient climate response

Severity of warming predicted by climate models depends on their Transient Climate Response (TCR). Inter-model spread of TCR has persisted at ~ 100% of its mean for decades. Existing observational constraints of TCR are based on observed historical warming response to historical forcing and their un...

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Bibliographic Details
Published in:Nature communications 2023-12, Vol.14 (1), p.8430-8430, Article 8430
Main Authors: Li, King-Fai, Tung, Ka-Kit
Format: Article
Language:English
Subjects:
704/106/694/1108
704/106/694/2786
Aerosols
Atmospheric models
Climate models
Climate prediction
Humanities and Social Sciences
multidisciplinary
Ocean models
Science
Science (multidisciplinary)
Sensitivity
Solar cycle
Statistical analysis
Time dependence
Uncertainty
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Summary:Severity of warming predicted by climate models depends on their Transient Climate Response (TCR). Inter-model spread of TCR has persisted at ~ 100% of its mean for decades. Existing observational constraints of TCR are based on observed historical warming response to historical forcing and their uncertainty spread is just as wide, mainly due to forcing uncertainty, and especially that of aerosols. Contrary, no aerosols are involved in solar-cycle forcing, providing an independent, tighter, constraint. Here, we define a climate sensitivity metric: time-dependent response regressed against time-dependent forcing, allowing phenomena with dissimilar time variations, such as the solar cycle with 11-year cyclic forcing, to be used to constrain TCR, which has a linear time-dependent forcing. We find a theoretical linear relationship between the two. The latest coupled atmosphere-ocean climate models obey the same linear relationship statistically. The proposed observational constraint on TCR is about 1 / 3 as narrow as existing constraints. The central estimate, 2.2  o C, is at the midpoint of the spread of the latest generation of climate models, which are more sensitive than those of the previous generations. Here, the solar-cycle forcing and response are used to constrain climate sensitivity. Solar forcing does not involve aerosols and thus provides an independent and tighter constraint, reducing current uncertainty range by 2/3.
ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-023-43583-7