DATE: FRIDAY, September 15, 2017 TIME: 2:30 P.M. - Room 223 (Refreshments served at 2:15 pm) PLACE: Environmental & Natural Resource Sciences Bldg. 14 College Farm Road, New Brunswick, New Jersey
Lorenzo Polvani
Columbia University
Why has the tropical lower stratosphere stopped cooling for the last 20 years?
The impact of ozone-depleting substances on global lower-stratospheric temperature trends is widely recognized. In the tropics, however, understanding lower-stratospheric temperature trends has proven more challenging. Using simple arguments based on observational evidence, combined with single-forcing model integrations, we show that trends in ozone-depleting substances, not well-mixed greenhouse gases, have been the primary driver of cooling in the tropical lower stratosphere from 1979 to 1997, and that this has occurred because ozone-depleting substances are key drivers of tropical upwelling and, more generally, of the entire Brewer–Dobson circulation. We will also discuss the impact of the Montreal Protocol on the future trends in the stratospheric circulation.