December 21, 2011

Winter 2011-12: Global Warming to Blame?

No matter what this winter holds in store, someone, somewhere, will blame it on global warming.

Recall that the last two snowy and cold winters in the eastern U.S. were blamed, by some, on greater than normal snowfall amounts across Eurasia during the preceding fall season. And the snowy Eurasian autumns were blamed on the low levels of Arctic sea ice during September—which of course was blamed on anthropogenic global warming. Forecaster Judah Cohen explained how this works in a Christmas day op-ed in the New York Times last year—published the day before a nearly 2 foot snowstorm buried the city:

“As global temperatures have warmed and as Arctic sea ice has melted over the past two and a half decades, more moisture has become available to fall as snow over the continents. So the snow cover across Siberia in the fall has steadily increased. … It’s all a snow job by nature. The reality is, we’re freezing not in spite of climate change but because of it.”

And back in January of 2000, during a particularly mild winter in New York City, the Times ran an article which blamed the mild, snowless weather on global warming:

“I bought a sled in ’96 for my daughter,” said Dr. Michael Oppenheimer, a scientist at the nonprofit Environmental Defense Fund. ”It’s been sitting in the stairwell, and hasn’t been used. I used to go sledding all the time. It’s one of my most vivid and pleasant memories as a kid, hauling the sled out to Cunningham Park in Queens.”

…Dr. Oppenheimer, among other ecologists, points to global warming as perhaps the most significant long-term factor.

But such is the cycle of the daily news. Anything unusual has to have a cause, and global warming has gone from being the cause du jour, to being the cause de rigueur. So you don’t have usually to look very far to find someone fingering global warming for anything meteorological—especially when it can be spun in a negative context.

So, what kind of global warming linkages should we expect from this year’s winter?

Well, Judah Cohen’s forecasting tool seems to be of little assistance this winter because the character of October snowfalls across Siberia seemed rather normal and thus it doesn’t have much portent power. According to a recent interview of Cohen in the Washington Post:

Siberian snow cover advanced at almost exactly the normal rate during most of October, with the exception of a dramatic expansion at the end of the month, which has Cohen a little nervous about this year’s forecast. Without a clear Siberian snow signal, he relied more on other factors to make his forecast, including the likelihood of continued La Niña conditions in the Pacific.

This all seems a bit odd to us, for the mechanism for snowy Octobers in Siberia, according to Cohen, is supposed to be a global warming-driven lack of September sea ice in the Arctic, and since the September sea ice this year was at a record or near-record low level (depending on your measure), you’d have thought that it would have been snowing like gangbusters in Siberia this fall. That it apparently wasn’t is evidence that global warming doesn’t seem to always produce big winter East Coast snowstorms via this mechanism (but only when someone says it does).

At other times, the global warming tie in that is advanced for big snows is that storms are more energetic and have more moisture in them on account of higher temperatures. Or, when it doesn’t snow at all and instead, sleet, freezing rain (or the combination that WCR’s Pat Michaels affectionately terms “sleeze”), or just plain rain occurs, then of course, global warming is tagged responsible for raising the temperature just enough to melt the snow before it hits the ground. Or, as the New York Times article from January 2000 attests, when winters are warm and pleasant, again, this is because of global warming—at least according to some “reliable” source.

So there is no escaping it—“it” being the accusation that global warming is responsible for whatever comes your way this winter.

And what may come your way this winter?

The figures below show the expectations from several organization which issue long-term forecasts. Figure 1 is from the Farmer’s Almanac, Figure 2 is from Accuweather, and Figure 3 is from the U.S. Climate Prediction Center.

All three forecasts for the upcoming winter basically show the same thing (with slight differences)—wet and cold in the northern tier of U.S. and milder in the southern portions of the country, with the Southwest being dry and the Southeast being a bit wetter than average.

Figure 1. The outlook for the winter of 2011-2012 according to the Farmer’s Almanac (available here).

Figure 2. The outlook for the winter of 2011-2012 according to Accuweather (available here)

Figure 3. The outlook for the winter of 2011-2012 according to the U.S. Climate Predication Center (available here)

The reason that they are all pretty similar is that they depict the pattern of weather which is typically expected as a result of La Niña conditions in the Pacific Ocean—conditions which are present currently and which are anticipated to continue through the winter. The caveat is that all La Niñas don’t necessarily produce weather over the continental U.S. that matches the above pattern. And thus far, the weather this December (the first month of climatological winter) has not been very typical of La Niña. Instead of the predominant (and expected) storm track being more or less west-to-east across the country, with storms entering from the Pacific Northwest, traversing through the Midwest and exiting across New England, storms have taken a more southerly route, entering through southern California, traversing the Southwest, crossing the central U.S. and leaving the country around the upper mid-Atlantic. This pattern has resulted in a cold West/warm East temperature pattern instead of the more La Niña-like warm South/cold North pattern and the regions receiving precipitation have been displaced southward.

We don’t profess to know whether this pattern will persist throughout the bulk of the winter yet to come, but clearly those in the business of providing seasonal forecasts don’t anticipate it to do so. The long-term (10-day) weather forecasting models indicate that the entrenched pattern is beginning to break down and be replaced by a more west-to-east (zonal) flow pattern typical of that expected from La Niña, but for how long the zonal flow (which is relatively unstable in the winter) will be maintained is largely unknowable.

As for global warming’s impacts this winter, well, it doesn’t seem as if it enters too much into the long-term climate forecasters way of thinking, being trumped instead by the anticipated natural variability related to La Niña conditions.

But just because no one is discussing it now, doesn’t mean that no one will attempt link it later.

Our forecast for winter 2011-2012—a high probability that someone somewhere will describe how the winter’s weather events are “consistent with” global warming from anthropogenic greenhouse gas emissions, whether it is warm, cold, wet, or dry. And whether it’ll be a blizzard of global warming hype, or just a drizzle, will depend on how disruptive the winter weather turns out to be.

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