Regional climate change projections from NA-CORDEX and their relation to climate sensitivity

Melissa S Bukovsky,Linda O Mearns

doi:10.1007/s10584-020-02835-x

Melissa S Bukovsky, Linda O Mearns

Open Access

https://doi.org/10.1007/s10584-020-02835-x

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Journal: Climatic Change	Publication Date: Sep 1, 2020
Citations: 30	License type: open-access

Affiliation: National Center for Atmospheric Research

Abstract

The climate sensitivity of global climate models (GCMs) strongly influences projected climate change due to increased atmospheric carbon dioxide. Reasonably, the climate sensitivity of a GCM may be expected to affect dynamically downscaled projections. However, there has been little examination of the effect of the climate sensitivity of GCMs on regional climate model (RCM) ensembles. Therefore, we present projections of temperature and precipitation from the ensemble of projections produced as a part of the North American branch of the international Coordinated Regional Downscaling Experiment (NA-CORDEX) in the context of their relationship to the climate sensitivity of their parent GCMs. NA-CORDEX simulations were produced at 50-km and 25-km resolutions with multiple RCMs which downscaled multiple GCMs that spanned nearly the full range of climate sensitivity available in the CMIP5 archive. We show that climate sensitivity is a very important source of spread in the NA-CORDEX ensemble, particularly for temperature. Temperature projections correlate with driving GCM climate sensitivity annually and seasonally across North America not only at a continental scale but also at a local-to-regional scale. Importantly, the spread in temperature projections would be reduced if only low, mid, or high climate sensitivity simulations were considered, or if only the ensemble mean were considered. Precipitation projections correlate with climate sensitivity, but only at a continental scale during the cold season, due to the increasing influence of other processes at finer scales. Additionally, it is shown that the RCMs do alter the projection space sampled by their driving GCMs.

Highlights

This study aims to examine the ensemble of projections produced as a part of the North American branch of the international Coordinated Regional Downscaling Experiment (NACORDEX) in the context of their relationship to the climate sensitivity of the global climate models (GCMs) used as forcing for this regional climate model (RCM) ensemble
Temperature and precipitation projections from 27 NA-CORDEX RCM simulations were assessed in the context of the transient climate response (TCR) of their driving GCMs
While precipitation projections do increase in magnitude with increasing TCR annually and in the cold season at a domain-mean scale, this relationship is not maintained at a local-to-regional scale, due to the increasing influence of local-to-regional process changes at those scales

Summary

Introduction

This study aims to examine the ensemble of projections produced as a part of the North American branch of the international Coordinated Regional Downscaling Experiment (NACORDEX) in the context of their relationship to the climate sensitivity of the global climate models (GCMs) used as forcing for this regional climate model (RCM) ensemble. A measure of the global mean temperature response to an increase in CO2, has been shown to be an important source of model uncertainty over large parts of the globe, and not just for nearsurface temperature (e.g., Mauritzen et al 2017). In GCMs, it is often measured in terms of the equilibrium (or “effective”) climate sensitivity (ECS), the global mean near-surface air temperature response to a doubling of CO2 after equilibrium is reached, or as a GCM’s transient climate response (TCR), the change in global mean temperature at the time CO2 reaches double its initial concentration while increasing at 1% per year.

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