Implications for Climate Change
Significant changes in surface radiative fluxes on decadal timescales have the potential to affect various aspects of climate change. Surface reaching radiative flux is the key determinant of surface air temperature. Despite solar dimming, the mean annual air temperature has been increasing due to increase in greenhouse gases. Earlier studies have shown that strong greenhouse forcing outweighs decreasing solar radiation (Philipona and Durr 2004 over Central Europe, Padmakumari et al. 2007 over the Indian subcontinent).
Several of earlier studies reported that radiative forcing is more effective in altering the strength of hydrological cycle than thermal forcing due to changes in the greenhouse gases. Pan evaporation (Epan) showed significant decreasing trend over different stations in India (Jaswal et al. 2008; Padmakumari et al. 2013). For the four decades considered, Epan showed high correlation with Rs (Fig. 8) as compared to surface air temperature and relative humidity (Padmakumari et al. 2013). The interpretation of variability in pan evaporation trends has been attributed to various reasons; most important among them is the changes in Rs. Vegetation growth, cover, and crop production are also affected by the changes in Rs.
Fig. 8 Comparison of observed surface reaching solar radiative flux (Rs) and pan evaporation (Epan) averaged for 11 stations for the period of 40 years (19712010)