From The Top Down

Aug 07 2020 | Ozone Image Credit: Courtesy of NASA.

The 2019 ozone hole reached a peak extent of 6.3 million square miles on September 8, the lowest maximum observed in decades.

"High Top" models are a special subset of climate models capable of capturing the inner workings of the stratosphere, the atmospheric layer sitting just above the jet stream.

The stratosphere is a curious place—winds there can race around at 120 mph, but storms are rare, and sudden warmings in this region often induce dramatic cold snaps down on Earth. The polar vortex resides in the stratosphere, as does the all-important ozone layer, which absorbs UV radiation, thereby protecting us from the sun’s harmful rays.

Much of Lorenzo Polvani’s work focuses on the peculiar chemistry of the stratosphere and the significant role it plays in climate change. An expert on ozone-depleting substances (ODS) regulated by the Montreal Protocol, his research has expanded our understanding not just of how these greenhouse gases affect that unique environment, but also of the broader impact of ODS on the entire climate system.

Lorenzo Polvani.

Since 1987, the Montreal Protocol has been hugely successful in healing the hole in the ozone layer by tightly regulating chlorofluorocarbons (CFCs) and other ODS substances that eat away at it. The role ODS play in climate change has been less widely appreciated. In early 2020, Polvani’s team published new insights into how ODS, whose impact can be 23,000-fold more potent than carbon dioxide, contributed specifically to warming in the Arctic and generally to global warming.

They determined that had ODS not been present over the past 50 years, only half the warming at the North Pole and a third of overall warming would have occurred. Their study provides a rare bit of good news; as ODS are phased out and drop from the atmosphere, their impacts will likewise fade.

“The profound link between global warming and ozone-depleting substances is only now beginning to be appreciated,” says Polvani, a senior scientist at of the Lamont Doherty Earth Observatory and the Maurice Ewing and J. Lamar Worzel Professor of Geophysics at Columbia Engineering. “Although most research has focused on carbon dioxide, it is now becoming clear that other greenhouse gases are also important. ODS are a good example. Not only did they create the ozone hole, but they have also been warming the planet. There’s so much more we need to learn.”