Black carbon aerosols and tropospheric ozone, both humanmade pollutants emitted predominantly in the Northern Hemisphere’s low- to mid-latitudes, are most likely pushing the boundary of the tropics further poleward in that hemisphere, new research shows. 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.

Today’s mega forest fires of the southwestern U.S. are truly unusual and exceptional in the long-term record, suggests an unprecedented study that examined 1,500 years of ancient tree ring and fire data from two distinct climate periods. Researchers constructed and analyzed a statistical model and found that today’s dry, hot climate combined with the past century of human fire suppression is causing megafires.