Tuesday, January 27, 2015

The Climate Science Behind New England’s Historic Blizzard
- by Joe Romm

Warming-fueled sea surface temperatures provide a boost of moisture for the forecast New England blizzard, just as it has for previous monster East Coast snow storms. (Credit: NOAA)  Click to Enlarge.
Another epic blizzard has born down on New England.  There is a “big part” played by “human-induced climate change,” especially warming-fueled ocean temperatures, according to Dr. Kevin Trenberth, former head of the Climate Analysis Section at the National Center for Atmospheric Research.

I asked Dr. Trenberth to comment on the role climate change has on this latest storm, which is forecast to set records.  He explained:
The number 1 cause of this is that it is winter.  In winter it is cold over the continent.  But it is warm over the oceans and the contrast between the cold continent and the warm Gulf Stream and surrounding waters is increasing. At present sea surface temperatures are more the 2F above normal over huge expanses (1000 miles) off the east coast and water vapor in the atmosphere is about 10% higher as a result.  About half of this can be attributed to climate change.
“Percent changes in the amount of precipitation falling in very heavy events (the heaviest 1%) from 1958 to 2012″ by region,” via the 2014 National Climate Assessment. “There is a clear national trend toward a greater amount of precipitation being concentrated in very heavy events, particularly in the Northeast,” driven by a warming climate. (Credit: 2014 National Climate Assessment) Click to enlarge.
Before this latest storm, we’ve seen a long-term pattern of more extreme precipitation, particularly in New England winters.  Climate scientists had long predicted this would happen in a warming world.
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That final point is very important.  The worst deluges have jumped not merely because warmer air holds more moisture that in turn gets sucked into major storm systems.  Increasingly, scientists have explained that climate change is altering the jet stream and weather patterns in ways that can cause storm systems to slow down or get stuck, thereby giving them more time to dump heavy precipitation (see my recent literature review here).

The National Climate Assessment noted that this “remains an active research area” but pointed out that:  “Heavier-than-normal snowfalls recently observed in the Midwest and Northeast U.S. in some years, with little snow in other years, are consistent with indications of increased blocking (a large scale pressure pattern with little or no movement) of the wintertime circulation of the Northern Hemisphere.”
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In the case of the blizzard bearing down on New England, we have both the extra moisture off the East Coast and an “odd configuration of the jet stream (once again) is moving the low pressure system through a pattern that will create an epic blizzard.”

Read more at The Climate Science Behind New England’s Historic Blizzard

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