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Posted on Sustainabilitank.info on February 11th, 2010
by Pincas Jawetz (pj@sustainabilitank.info)

nbsp;www.tnr.com/blog/the-vine/what-th…

What The Snowpocalypse Tells Us About Global Warming.
by Bradford Plumer, February 10, 2010, The New Republic online

Washington D.C.’s getting slammed by record snowfall right now, which means that in addition to unplowed roads and Mad Max-style scenes at Safeway, we also have to suffer through a flurry of Al Gore jokes and Republicans snorting about how this proves global warming is all fake. I guess the prim, boring response is that a single weather event, even an extreme one, doesn’t tell us very much about long-term climate trends. But blah, blah, everyone’s heard that line before.

A more thoughtful reply comes from meteorologist Jeff Masters, who explains how massive snowstorms in the Northeast are, in fact, quite consistent with a steadily warming world:

There are two requirements for a record snow storm:

1) A near-record amount of moisture in the air (or a very slow moving storm).

2) Temperatures cold enough for snow.

It’s not hard at all to get temperatures cold enough for snow in a world experiencing global warming.

According to the 2007 Intergovernmental Panel on Climate Change (IPCC) report, the globe warmed 0.74°C (1.3°F) over the past 100 years. There will still be colder than average winters in a world that is experiencing warming, with plenty of opportunities for snow.

The more difficult ingredient for producing a record snowstorm is the requirement of near-record levels of moisture.

Global warming theory predicts that global precipitation will increase, and that heavy precipitation events–the ones most likely to cause flash flooding–will also increase. This occurs because as the climate warms, evaporation of moisture from the oceans increases, resulting in more water vapor in the air.

According to the 2007 Intergovernmental Panel on Climate Change (IPCC) report, water vapor in the global atmosphere has increased by about 5% over the 20th century, and 4% since 1970. This extra moisture in the air will tend to produce heavier snowstorms, assuming it is cold enough to snow. Groisman et al. (2004) found a 14% increase in heavy (top 5%) and 20% increase in very heavy (top 1%) precipitation events in the U.S. over the past 100 years, though mainly in spring and summer. However, the authors did find a significant increase in winter heavy precipitation events have occurred in the Northeast U.S.

This was echoed by Changnon et al. (2006), who found, “The temporal distribution of snowstorms exhibited wide fluctuations during 1901-2000, with downward 100-yr trends in the lower Midwest, South, and West Coast. 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.”

Meanwhile, it’s worth noting the U.S. Global Change Research Program actually predicted stronger winter storms for the Northeast, in its 2009 report on potential climate-change impacts for the United States:

Storm tracks have shifted northward over the last 50 years as evidenced by a decrease in the frequency of storms in mid-latitude areas of the Northern Hemisphere, while high-latitude activity has increased. There is also evidence of an increase in the intensity of storms in both the mid- and high-latitude areas of the Northern Hemisphere, with greater confidence in the increases occurring in high latitudes (Kunkel et al., 2008). The northward shift is projected to continue, and strong cold season storms are likely to become stronger and more frequent, with greater wind speeds and more extreme wave heights.”

Now, that doesn’t mean we can definitely say that global warming caused this snow monstrosity—again, it’s too hard to attribute any single weather event to long-term climate shifts. (For instance, El Niño may be playing a bigger role right now in feeding these storms.) At most, we can say that a warming climate will create the conditions that make fierce winter storms in the Northeast and mid-Atlantic more likely. Or at least it will for awhile: If the planet keeps heating up, then at some point freezing conditions in the Northeast will become very rare, at which point snowstorms will, too But we’re not at that point—the Earth hasn’t warmed that much yet.

On the other hand, climate models do predict that snowstorms in the southernmost parts of the United States should become much rarer in the coming decades: There’s plenty of moisture down south, but freezing temperatures are likely to decrease and the jet stream is expected to shift northward. So if those regions start seeing a sustained uptick in snowfall, then something’s gone awry in climate predictions. But the blizzard in the Northeast, while miserable and incredibly disruptive, doesn’t appear whack with long-term forecasts. (That’s not exactly cheerful news for those of us who have to live here.)

—————
Dr. Jeff Masters’ WunderBlog

Last Updated: 1:02 PM GMT on February 11, 2010.
Heavy snowfall in a warming world.

Posted by: JeffMasters on February 08, 2010

A major new winter storm is headed east over the U.S. today, and threatens to dump a foot or more of snow on Philadelphia, New York City, and surrounding regions Tuesday and Wednesday. Philadelphia is still digging out from its second top-ten snowstorm of recorded history to hit the city this winter, and the streets are going to begin looking like canyons if this week’s snowstorm adds a significant amount of snow to the incredible 28.5″ that fell during “Snowmageddon” last Friday and Saturday. Philadelphia has had two snowstorms exceeding 23″ this winter. According to the National Climatic Data Center, the return period for a 22+ inch snow storm is once every 100 years–and we’ve had two 100-year snow storms in Philadelphia this winter. It is true that if the winter pattern of jet stream location, sea surface temperatures, etc, are suitable for a 100-year storm to form, that will increase the chances for a second such storm to occur that same year, and thus the odds have having two 100-year storms the same year are not 1 in 10,000. Still, the two huge snowstorms this winter in the Mid-Atlantic are definitely a very rare event one should see only once every few hundred years, and is something that has not occurred since modern records began in 1870. The situation is similar for Baltimore and Washington D.C. According to the National Climatic Data Center, the expected return period in the Washington D.C./Baltimore region for snowstorms with more than 16 inches of snow is about once every 25 years. This one-two punch of two major Nor’easters in one winter with 16+ inches of snow is unprecedented in the historical record for the region, which goes back to the late 1800s.

Top 9 snowstorms on record for Philadelphia:

1. 30.7″, Jan 7-8, 1996
2. 28.5″, Feb 5-6, 2010 (Snowmageddon)
3. 23.2″, Dec 19-20, 2009 (Snowpocalypse)
4. 21.3″, Feb 11-12, 1983
5. 21.0″, Dec 25-26, 1909
6. 19.4″, Apr 3-4, 1915
7. 18.9″, Feb 12-14, 1899
8. 16.7″, Jan 22-24, 1935
9. 15.1″, Feb 28-Mar 1, 1941

The top 10 snowstorms on record for Baltimore:

1. 28.2″, Feb 15-18, 2003
2. 26.5″, Jan 27-29, 1922
3. 24.8″, Feb 5-6, 2010 (Snowmageddon)
4. 22.8″, Feb 11-12, 1983
5. 22.5″, Jan 7-8, 1996
6. 22.0″, Mar 29-30, 1942
7. 21.4″, Feb 11-14, 1899
8. 21.0″, Dec 19-20, 2009 (Snowpocalypse)
9. 20.0″, Feb 18-19, 1979
10. 16.0″, Mar 15-18, 1892

The top 10 snowstorms on record for Washington, D.C.:

1. 28.0″, Jan 27-28, 1922
2. 20.5″, Feb 11-13, 1899
3. 18.7″, Feb 18-19, 1979
4. 17.8″ Feb 5-6, 2010 (Snowmageddon)
5. 17.1″, Jan 6-8, 1996
6. 16.7″, Feb 15-18, 2003
7. 16.6″, Feb 11-12, 1983
8. 16.4″, Dec 19-20, 2009 (Snowpocalypse)
9. 14.4″, Feb 15-16, 1958
10. 14.4″, Feb 7, 1936

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