THE VINE FEBRUARY 10, 2010
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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, simply doesn't tell us 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 why massive snowstorms in the Northeast aren't inconsistent 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."
Still, we can't definitively say that global warming caused this snow monstrosity—again, it's impossible 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 snowstorms.) At most, we can say that a warming climate is expected, over time, to 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 in theory freezing conditions in the Northeast will become rarer, at which point snowstorms would, too. But we're not at that point—the Earth hasn't warmed that much yet.
On the other hand, climate models do project that snowstorms in the southernmost parts of the United States should become less frequent 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 one blizzard in the Northeast, while miserable and incredibly disruptive, isn't out of whack with long-term forecasts. (That's not exactly cheerful news for those of us who have to live here.)
(Flickr photo credit: errisiva)
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9 comments
Thanks for this. It will make a handy link for me to post elsewhere.
- frippo
February 10, 2010 at 1:56pm
This increase in atmospheric moisture thanks to El Nino as well as GCC also explains the record breaking amounts of rain received in New Orleans during the month of December. 22.5 inches fell compared to the monthly average of 5 inches. In one 24-hour period we received 11 inches of rain. Never in my life have I seen it rain so hard and for so long.
- singlspeed
February 10, 2010 at 6:52pm
From Katrina to global warming to climate change to snowpocalypse, this whole discussion seems like we're reverting to primitive tribal beliefs where the chief priest caused the rain to fall. There is zero evidence that the current snowstorms have anything to do with global warming or the lack thereof. TNR and Drudge should stop pandering to public superstitions and leave weather reporting to the local weather reporters.
- dtohmatsu
February 10, 2010 at 9:47pm
There is a long range trend toward warming. Anthropogenic activity has a high probability of playing a role. I believe that the alarmists exaggerate this role and that the science they present to support their alarmist predictions is very thin. They look foolish when they claim one year that the abnormally warm winter proves their case, and in another year claim that an abnormally cold winter also proves their case.
- r.ennis
February 11, 2010 at 9:02am
What a strained and twisting attempt to wedge a statistically insignificant event into an increasingly tenuous theory. Why even bother? Especially when you rely on IPCC reports. The blogger protests too much, methinks.
- emccded
February 11, 2010 at 10:02am
The AGW folks have pretty much lost all credibility. The major proponents are in it for the money, the serious followers are in it out of visceral hatred and desired revenge on globalism and modern economies. The rest are sheep too scared to go against "mob thinking". Unfortunately it is likely too late to stop governments from doing foolish and expensive things to "stop global warming". The climate is changing as it has done "since the beginning". We didn't cause it. We must learn to live with it.
- hingston
February 11, 2010 at 10:17am
Wow, what a bunch of ignorant hotheads. It is happening, and every one of you fools who sticks your head in the sand should be strapped to a fence in your skivvies and forced to endure every last one of these nor'easter snowstorms back to back. The whole point is that weather phenomena, should current trends continue, will generally be more extreme--worse storms, worse droughts. The science has been there for quite a while, for those willing to get their heads out of their arses long enough to read without their thumb-sucking intellectual blinders and bigotries getting in the way.
- cspencef
February 11, 2010 at 11:23am
cspencef is correct. The problem is with the nomenclature ie, "global warming". This allows for "ha ha--we're getting record cold temps/snow storms; so m uch for global warming, blah blah blah". "Global climate change" is really what is happening. And yes hingston (I almost wanted to say "unhingedston"), it HAS been happening since the beginning and we DO have to learn to live with it. But human activity HAS accelerated the detrimental changes and more important, non-essential human activity at that. We can only control what we can control and we must control what we can control. The planet will go on regardless of weather patterns but where humans can live will decrease (and I doubt our numbers will be dwindling in proportion) as well the amount of space for food production and the amount of drinkable water will also decrease. As a childless person, I don't have too much of a stake in this but I still want humanity to rise to this challenge honorably and not greedily or stupidly.
- ericad
February 11, 2010 at 3:23pm
What this is really about is the inability of some people to understand the difference between weather in one spot, and climate averaged over the globe? Cold snap in the eastern US because an arctic air mass has moved south? Well, look at where the arctic air came from and you find that the temperatures there are way above average because the cold air was replaced by warmer air that moved north. Surprise! What does it tell you about climate change? On its own, virtually nothing. Ditto for this snowstorm. There are good reasons to expect that events like this will become more likely (for a while) as the planet warms up. If you live far enough north, you will realize that snowfall is not about cold, but about water. Where I live in the winter, it has to warm up to snow -- we can't get more than a trace of snowfall when it is very cold because there is not enough water in the air. But even so, if the probability of something happening goes up from 5% to 6%, when it happens you can never *prove* that this one event is the extra one that would not have happened otherwise. You can only deal with it probabilistically. So I think it just confuses matters to even go down that road.
- JEFF FREY
February 11, 2010 at 7:46pm