Importance of constraining the pattern effect during the historical period for future temperature projection
Abstract
Recent studies have shown that climate feedback parameter is dependent upon evolving pattern of surface warming. This so-called pattern effect can occur due both to radiatively forced response and internal climate variability, and it had hindered to reconcile estimates of equilibrium climate sensitivity (ECS) from climate models and observational records. Despite its cause, uncertainty in the pattern effect is far from negligible when narrowing the range of future global-mean temperature increase with a given emission scenario. Here we demonstrate using an emulator based on the Held-Winton two-layer model that the future temperature projection for a given range of the ECS can be narrowed by constraining an efficacy parameter representing the forced pattern effect referring to the past observed warming for 1961-2014. For a range of ECS assessed in the IPCC AR6, we identified that parameters which enable the emulator to fit observations are a set of either a high ECS/strong pattern effect or a low ECS/weak pattern effect, and a very low ECS is not supported by a physical condition of the pattern effect greater than unity. This suggests that estimate of the pattern effect parameter based on an independent line of evidence, if possible, can be used to validate the assessed range of ECS. However, the constraint to the pattern effect by referring to the observed warming is influenced by uncertainty due to aerosol radiative forcing and internal climate variability, of which contribution is still a challenge.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.A55D..02W