Contribution of external forcings to the observed trend in surface temperature over Africa during 1901-2014 and its future projection from CMIP6 simulations

Previous studies revealed that many areas in Africa experienced an apparent warming rate in surface temperature in the last century. However, the contributing factors have not been investigated in details. In the present study, natural and anthropogenic forcings accountable for surface temperature variability and change are examined from the historical Coupled Model Inter-comparison Project phase six (CMIP6) simulations and future projections under three Shared Socioeconomic Pathways (SSP1-2.6, SSP2.4.5 and SSP5-8.5), which represent low, moderate and high emission scenarios, respectively. Results indicate that from 1901 to 2014, surface temperature has increased by similar to 0.07 degrees C/decade over both Eastern Africa (EAF) and Sahara (SAH) regions, 0.06 degrees C/decade in Southern Africa (SAF) and Western Africa (WAF) regions and follows the global warming trend. It is found that Greenhouse Gases (GHG) and Land-Use (LU) change are the leading contributors to the observed warming in historical surface temperature over Africa. Anthropogenic Aerosols (AA) show a cooling effect on surface temperature. Under both SSP1-2.6 and SSP2-4.5 emission scenarios, the surface temperature increases to 2059 and declines afterwards. On the other hand, under SSP5-8.5, the surface temperature is expected to increase throughout the 21st century. The impacts of warming will be hard-felt in SAH and SAF regions compared to other areas. The analysis of rare hot and cold events (2080-2099) based on the 20-year annual highest and lowest daily surface temperature relative to the recent past (1995-2014) under SSP2-4.5 indicates that both events are likely to increase significantly in the later 21st century. Nevertheless, proper management of Land use and control of anthropogenic factors (GHGs and AA) may lead to a substantial reduction in further warming over Africa.

Automated summary

The study shows that the warming of surface temperature in Africa is associated with greenhouse gases and land-use changes, while anthropogenic aerosols have a cooling effect. Depending on different emission scenarios, the surface temperature in Africa is projected to continue to increase or decrease in the coming decades, with Sahara and Southern Africa experiencing more severe impacts. Based on the simulation results, it is likely that the number of rare hot and cold events will significantly increase in the later 21st century.