Assessing Regional Climate Trends in West Africa Under Geoengineering: A Multimodel Comparison of UKESM1 and CESM2

Abstract

This study investigates West Africa's climate vulnerability under stratospheric aerosol injection (SAI), using UKESM1 and CESM2 models. We analyzed temperature and precipitation responses for 2050–2069 relative to 2015–2034 under SSP2-4.5 and ARISE-SAI-1.5 scenarios. Our approach involved evaluating temperature and precipitation anomalies, applying signal-to-noise ratio (SNR) analysis—defined as the ratio of the forced climate response to internal variability—to assess signal robustness, and using cumulative distribution (CDF) and probability density (PDF) functions to explore shifts in precipitation extremes. Results indicate that under SSP2-4.5, both models project significant warming. UKESM1 simulates increases near 1.8°C, while CESM2 projects between 1.0°C and 1.2°C. Under ARISE-SAI-1.5, UKESM1 shows pronounced cooling, with temperatures dropping up to 0.3°C below the reference period at some latitudes. CESM2 shows a more uniform cooling, with temperatures between 0°C and 0.3°C above the reference. SNR analysis reveals robust, statistically significant temperature changes across the region, clearly emerging above natural variability by midcentury. Precipitation changes, however, show lower SNR values and greater spatial uncertainty, suggesting weaker and less predictable hydrological responses. CDF and PDF analyses highlight complex shifts in precipitation extremes, suggesting that while SAI could counteract warming trends, it may introduce additional variability and uncertainty in rainfall projections. These results emphasize the importance of multimodel comparisons in assessing geoengineering impacts on regional climates, as differing sensitivities to radiative forcing and feedback can produce divergent outcomes.