Precipitation and temperature response to sea salt injection into low marine clouds over West Africa

Abstract

Sea salt injection into the tropical marine clouds is evaluated for its potentials to reduce the negative impact of the prevailing global warming over West Africa. Radiative forcing is determined as the intercept of the regression of response of radiation parameter to that of surface air temperature. The seasonal responses of temperature and precipitation to geoengineering over West Africa are analysed using temperature and precipitation outputs from IPSL-M5A-LR with three different forcing scenarios. The three scenarios are historical greenhouse gas concentrations, Representative Concentration Pathway 4.5 W/m2 scenario (RCP4.5) and combination of RCP4.5 and geoengineering forcing (sea salt climate engineering, G5). 20-year means in the middle of G5 (2045–2064) are considered for the future period, and the historical climatology from 1986 to 2005 is used. Net downward flux and top of atmosphere outgoing shortwave radiation have negative forcing only at the western Sahel. The G5 reduces the warming in the RCP4.5 scenario over the whole of West Africa. It also shifts ITCZ northward with respect to RCP4.5, thereby increasing wetness over most of the land areas. The areas with wetness response have anomalous westerly with respect to RCP 4.5 and latitudinal location below anomalous easterly wind. Results show that G5 is effective in reducing the RCP4.5 projected warming up to 1.2 K and increasing wetness over most land areas. The G5 has a damaging effect on the temperature pattern at the southern ocean and coastal areas, while it has damaging effect on precipitation patterns at some parts of the Sahel.