An University of California – Riverside led team has identified black carbon and tropospheric ozone as the most likely drivers of large-scale atmospheric circulation change in the Northern Hemisphere tropics zone. While stratospheric ozone depletion has already been shown to be the primary driver of the expansion of the tropics in the Southern Hemisphere, the researchers are the first to report that black carbon and tropospheric ozone are the most likely primary drivers of the tropical expansion observed in the Northern Hemisphere.