CO2 radiative forcing induces summer cooling over India

In response to anthropogenic forcing, the Earth’s surface generally warms as greenhouse gases trap outgoing longwave radiation. Counterintuitively, however, some regions exhibit surface cooling against this global warming background—a phenomenon known as a warming hole. Beyond the well-documented warming holes over the North Atlantic and southeastern United States, here we show that increasing atmospheric CO2 concentrations can also induce summertime cooling over India. Due to the direct radiative effect of CO2, warming of the Eurasian continent relative to surrounding oceans, low-level moisture transport and vertical motion are enhanced over India. Combined with abundant summer-monsoon moisture and the topographic blocking effects of the Himalayas and Hindu Kush Mountains, these circulation changes increase cloud cover. The resulting cloud enhancement reduces incoming solar radiation at the surface, producing the observed regional cooling. These results reveal a previously underappreciated mechanism whereby greenhouse gas forcing can paradoxically induce regional cooling through atmospheric dynamical pathways. Rising atmospheric CO2 concentrations can paradoxically induce summer surface cooling over India. This is happening via an atmospheric dynamical pathway, wherein enhanced Eurasian warming increases cloud cover and reduces solar radiation, leading to regional cooling over India in summer.