Tuesday, March 20, 2018

Bomb Cyclones, Nor’easters, and the Messy Relationship Between Weather and Climate

After three frigid nor’easters in less than two weeks, even the most devout prophet of climate change could be forgiven for echoing the sentiment that President Trump tweeted a few months ago, to much ridicule, shortly before one of the coldest New Year’s Eves on record: “Perhaps we could use a little bit of that good old Global Warming.” By this point, most people outside the White House understand that climate is not the same as weather—that climate is the forest and weather is the trees. Yet the global climate system is enormously complex, and there is, in fact, a lively scientific debate in progress about the relationship between human-caused climate change (especially in the Arctic) and the increased frequency of extreme cold-weather events across the United States—blizzards, bomb cyclones, and the dreaded wintry mix.

The debate began in late 2011, at a meeting in San Francisco of the American Geophysical Union, when an atmospheric scientist named Jennifer Francis gave a talk that electrified her colleagues. Perhaps, she suggested, the persistent outbreaks of extreme weather that people were experiencing in the Northern Hemisphere were connected to the colossal loss of sea ice in the Arctic—a region that, with increasing greenhouse-gas emissions, has warmed at double the rate of the rest of the planet. Up until that moment, while scientists knew that the Arctic was changing rapidly—since the nineteen-seventies, sea ice, snow cover, and glaciers had all declined dramatically, and the permafrost was starting to thaw—they did not think it had an influence on weather systems in the midlatitudes. Credit for that went entirely to the tropics. Read More