What Role Is Climate Change Playing in Historic New England Blizzard?

http://thinkprogress.org/climate/2013/02/08/1561331/epic-blizzard-poised-to-strike-new-england-what-role-does-climate-change-play/

By Joe Romm on Feb 8, 2013

An epic blizzard is bearing down on New England — fed in part by relatively warm coastal waters.

I asked Dr. Kevin Trenberth, former head of the Climate Analysis Section at the National Center for Atmospheric Research, to comment on the role climate change has on this storm. He explained:

This is a perfect set up for a big storm, with the combination of two parts: a disturbance from the Gulf region with lots of moisture and a cold front from the west.
Ingredients for a big snow storm include temperatures just below freezing. In the past temperatures at this time of year would have been a lot below freezing but the ability to hold moisture in the atmosphere goes down by 7% per degree C (4% per deg F), and so in the past we would have had a snow storm but not these amounts.
The moisture flow into the storm is also important and that is enhanced by higher than normal sea surface temperatures (SSTs). These are higher by about 1 deg C [almost 2°F] than a normal (pre-1980) due to global warming and so that adds about 10% to the potential for a big snow.

Every storm and “event” is unique. It always has unique ingredients. So it is hard if not impossible to take apart, because any piece missing means the storm behaves differently. So event attribution is not well posed. Instead we look for the environment in which the storm is occurring and how that has changed to make conditions warmer and moister over the oceans.

Like a baseball player on steroids, our climate system is breaking records at an unnatural pace. And like a baseball player on steroids, it’s the wrong question to ask whether a given home run is “caused” by steroids. As Trenberth wrote in his must-read analaysis, “How To Relate Climate Extremes to Climate Change,” the “answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.”

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Heavy precipitation events in the Northeast, including both rain and snowstorms, have been increasing in the past few decades, in a trend that a new federal climate report links to manmade global climate change. As the world has warmed, more moisture has been added to the atmosphere, giving storms additional energy to work with, and makingprecipitation extremes more common in many places.

Trenberth’s second point is an important one — warmer than normal winters favor snow storms (See “We get more snow storms in warm years“). A 2006 study, “Temporal and Spatial Characteristics of Snowstorms in the Contiguous United States“ found we are seeing more northern snow storms and that we get more snow storms in warmer years:

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The other big impact of global warming on the destructiveness of superstorms like this (and Sandy) is sea level rise:

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Rising sea levels due to warming seas and melting ice caps are already making typical nor’easters such as the upcoming event more damaging, since they provide the storms with a higher launching pad for causing coastal flooding. According to the draft National Climate Assessment report released in January, even without any changes in storms, the chance of what is now a 1-in-10-year coastal flood event in the Northeast could triple by 2100, occurring once every 3 years, due to rising sea levels.

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According to research by Climate Central scientists, the sea level trend in Boston Harbor from 1959 to 2008 in Boston Harbor has been 2.31 milimeters per year, which is slightly below the global average over the same period. In the past 50 years, the water level has risen by about 4.5 inches at that location, although it has increased much more in other spots along the northeastern coast.

On Nantucket Island, where coastal flooding is anticipated from this storm along with hurricane-force winds, the sea level has risen by about half a foot during the past 50 years.

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