Determine the source of feedback bias in atmosphere-only simulations

Determine whether the bias between amip-type and coupled CESM2 simulations is caused by missing atmosphere–ocean coupling or by the small sample size used in the experiments.

Background

The paper compares atmosphere-only amip-piForcing and amip-histForcing simulations with fully coupled CESM2 historical simulations that have identical sea-surface temperatures and sea-ice concentrations. Prescribing atmospheric forcing improves agreement between the atmosphere-only and coupled feedback estimates, but substantial discrepancies remain even when SSTs, SIC, and atmospheric forcing are identical.

The authors identify two possible explanations for the remaining bias: the absence of atmosphere–ocean coupling in the atmosphere-only configuration, or the limited ensemble size. They explicitly leave the distinction unresolved and outside the scope of the study.

References

Whether the bias between amip-type and coupled simulations seen in Fig.~\ref{fig:feedbacks_amipHistForcing}a is a result of the missing atmosphere-ocean coupling in amip, or is merely an effect of the small sample size, remains unclear and is beyond the scope of this study.

— Statistical Noise and Missing Forcing Limit Estimates of Earth's Feedback from Prescribed Sea-Surface Temperature Simulations  (2608.13219 - Gyuleva et al., 13 Aug 2026) in Section 3.1, subsection “Comparing amip-piForcing-style and coupled runs with identical SSTs & SIC”

The true response is unknown, but it is unlikely far outside the AMIP uncertainty.

— How Do AI Climate Models Respond to Warming Across Climate Zones?  (2608.17986 - Merchant et al., 18 Aug 2026) in Conclusion and Discussion