Climate Change and Winter Storm Nemo
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.”
On the warmer SSTs, Climate Central’s Andrew Freedman explains:
As was the case when Hurricane Sandy struck in late October, sea-surface temperatures are running a couple degrees above average off the East Coast, which according to climate scientists may reflect both natural climate variability and the effects of manmade global warming.
The presence of unusually warm waters could aid in the rapid development of the storm system, and infuse it with additional moisture, thereby increasing snowfall totals.
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.
Sea surface temperature anomalies off the East Coast. Credit Wunderground/NOAA via CC.
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:
The temporal distribution of snowstorms exhibited wide fluctuations during 1901-2000…. Upward trends occurred in the upper Midwest, East, and Northeast, and the national trend for 1901-2000 was upward, corresponding to trends in strong cyclonic activity….
Assessment of the January-February temperature conditions again showed that most of the United States had 71%-80% of their snowstorms in warmer-than-normal years…. a future with wetter and warmer winters, which is one outcome expected (National Assessment Synthesis Team 2001), will bring more snowstorms than in 1901-2000. Agee (1991) found that long-term warming trends in the United States were associated with increasing cyclonic activity in North America, further indicating that a warmer future climate will generate more winter storms.
The U.S. Global Change Research Program (USGCRP) U.S. Climate Impacts Report from 2009 reviewed that literature and concluded, “Cold-season storm tracks are shifting northward and the strongest storms are likely to become stronger and more frequent.
So it is no surprise that a 2012 study found extreme snowstorms and deluges are becoming more frequent and more severe. Freedman points out:
For the northern hemisphere as a whole, winter storms have become more common and intense during the past 50 years, according to the draft federal report. Observed changes in winter air circulation in the northern hemisphere, possibly related to Arctic sea ice loss, has been linked to large swings in seasonal snowfall from one winter to the next in the Northeast. Other studies indicate that as global warming continues, nor’easters such as the one about to hit New England may become more frequent in this region, and less common in the Mid-Atlantic states, as storm tracks shift closer to the poles.
Again, the Northeast has been especially vulnerable to deluges and Snowmaggedons, experiencing a sharp increase in one-day precipitation extremes during the October to March cold season:
The other big impact of global warming on the destructiveness of superstorms like this (and Sandy) is sea level rise:
The coastal flooding threat for this storm in New York pales in comparison to what it was during Hurricane Sandy, when large parts of the city’s iconic subway system flooded in the face of a record storm surge, and many New Yorkers drowned in flood waters.
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.
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.
People should take the weather forecasts of this storm seriously and act accordingly.
Similarly, the nation should take seriously the climatic projections of ever worsening storms from global warming — and act accordingly.
Joe Romm is a Fellow at American Progress and is the editor of Climate Progress, which New York Times columnist Tom Friedman called "the indispensable blog" and Time magazine named one of the 25 "Best Blogs of 2010." In 2009, Rolling Stone put Romm #88 on its list of 100 "people who are reinventing America." Time named him a "Hero of the Environment″ and “The Web’s most influential ...
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