Evaluation and projection of mean surface temperature using CMIP6 models over East Africa

Brian Ayugi,Hamida Ngoma,Hassen Babaousmail,Rizwan Karim,Vedaste Iyakaremye,Kenny T.C Lim Kam Sian,Victor Ongoma

doi:10.1016/j.jafrearsci.2021.104226

Abstract

This study evaluates the historical mean surface temperature (hereafter T2m) and examines how T2m changes over East Africa (EA) in the 21st century using CMIP6 models. An evaluation was conducted based on mean state, trends, and statistical metrics (Bias, Correlation Coefficient, Root Mean Square Difference, and Taylor skill score). For projections over EA, five best performing CMIP6 models (based on their performance ranking in historical mean temperature simulations) under the shared socioeconomic pathways SSP2-4.5 and SSP5-8.5 scenarios were employed. The historical simulations reveal an overestimation of the mean annual T2m cycle over the study region with fewer models depicting underestimations. Further, CMIP6 models reproduce the spatial and temporal trends within the observed range proximity. Overall, the best performing models are as follows: FGOALS-g3, HadGEM-GC31-LL, MPI-ESM2-LR, CNRM-CM6-1,andIPSL-CM6A-LR. During the three-time slices under consideration, the Multi Model Ensemble (MME) project many changes during the late period (2080–2100) with expected mean changes at 2.4 °C for SSP2-4.5 and 4.4 °C for the SSP5-8.5 scenario. The magnitude of change based on Sen's slope estimator and Mann-Kendall test reveal significant increasing tendencies with projections of 0.24 °C decade-1 (0.65 °C decade-1) under SSP2-4.5(SSP5-8.5) scenarios. The findings from this study illustrate higher warming in the latest model outputs of CMIP6 relative to its predecessor, despite identical instantaneous radiative forcing.

Highlights

The global mean surface temperature (GMST) records continue to set new levels year after year from 2011 to present (IPCC, 2018; WMO, 2020)
This study examined the capability of CMIP6 models in reproducing the observed T2m as detected by Climatic Research Unit (CRU)
Evaluation of T2m was conducted based on mean state, trends, bias, CC, RMSE and Taylor skill score

Summary

Introduction

The global mean surface temperature (GMST) records continue to set new levels year after year from 2011 to present (IPCC, 2018; WMO, 2020). Despite the global impacts of coronavirus disease (COVID-19), the year 2020 stood to be the warmest year, with new records set to about 1.2 °C above the pre-industrial (1850 – 1900) level (WMO, 2020). Comparative analysis before and after the 1950s reveals an amplification of extreme events resulting from heightened warming of global land and ocean (IPCC, 2014). Efforts to mitigate the impacts of global warming levels (GWLs) to below 2 °C or even much more preferred targets of 1.5 °C under current greenhouse levels (GHGs) remains an elusive ambition despite the efforts by United Nations Framework Convention on Climate Change (UNFCCC) Paris Agreement (UNFCCC, 2015). In order to stabilize the GMST from further upward trajectories, concerted energies from all stakeholders will be required to devise appropriate and urgent actions to guide the earth system from crossing the threshold to the worst-case scenario of “Hothouse Earth” (Steffen et al, 2018)

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Conclusion