Monday, February 23, 2015

Yes It Still Gets Cold In Winter

AKA: Weather is not Climate

Recently seen headlines at WUWT:

Great Lakes Ice Coverage In Striking Distance of a Record

Eastern U.S. record breaking cold and snow as seen from space

Friday Funny Bonus: East Coast Frozen Blizzard Edition

4 of the 5 Great Lakes about to freeze over

Conclusion:  CO2-driven global warming is a farce.

Except not really ...

All the way back on January 26, 2015, the Washington Post put things into context: Global warming could make blizzards worse

Alarmist?  Perhaps.  It depends on whether one chooses to be alarmed.  Personally I like keeping my wits about me when considering the possibility of future threats, especially when they're also quite possibly avoidable.  That means I want to be made aware of potential threats so that I can exercise concern of the sort which leads to taking action.

Let's see what the article says:
We’re on the verge of another historic blizzard, with as much as two or three feet of snow expected in parts of the Northeast. Already, the press is throwing around terms like “Snowmageddon” to describe what’s coming. Next comes politics: Whenever the East Coast sees an extreme snow event, the weather is perfect for snow trolling – e.g., trying to use one cold event to refute a warming climate trend.
Ayup.  So, what's really going on?
In this case that’s particularly inappropriate, though, because if anything, extreme snowfall may actually be enhanced by global warming. I know it sounds counterintuitive, but remember that even in a warming world, our hemisphere will still spend part of the year tilted away from the sun, with shorter days and colder temperatures — and winter storms.

The question scientifically, then, is what happens to those storms in a warmer world. So let’s examine what science can say about that question.

Technically, the storm about to slam the Northeast is called — that’s right — a nor’easter. What’s special about these storms is that they draw their energy from a temperature clash between freezing Arctic air on the one hand, and warmer Gulf Stream waters on the other.
Emphasis added.  Now for some color commentary from a few experts:
“The U.N. Intergovernmental Panel on Climate Change has found that nor’easters like this one may grow stronger [with] human-caused climate change, as they are driven by the contrast between cold Arctic air masses and ever-warming ocean surface temperatures,” says Penn State climatologist Michael Mann.

“We also know that ocean surface temperatures off the U.S. east coast right now are unusually warm, and there is no doubt that a component of that anomalous warmth is due to human-caused climate change,” Mann adds. “Those warm ocean temperatures also mean that there is more moisture in the air for this storm to feed on and to produce huge snowfalls inland.”

That does not, of course, mean the current storm is caused by climate change. Rather, says Mann, it means that climate change may make certain aspects of the event worse, such as its snowfall.
Emphasis mine again.  I can't overemphasize the nuance here enough -- intensifying storms (all seasons) are not inconsistent with global warming, they are in fact predicted -- HOWEVER, take care to NOT say that a particular weather event is a smoking-gun sign that your particular belief about AGW is either confirmed or falsified.

Or in short-form: climate is the statistics of weather over multiple decades, not a single weather event, or indeed not an "anomalous" season of hot/cold stormy/calm.

In shortest form: climate is not weather.  If you find yourself tempted to go there, best consult with what real experts have to say:
Kevin Trenberth, a climate researcher at the National Center for Atmospheric Research, is willing to get very specific about just how much climate trends may influence this storm. “At present sea surface temperatures are more [than] 2 F above normal over huge expanses (1000 miles) off the east coast and water vapor in the atmosphere is about 10 percent higher as a result,” he says. “About half of this can be attributed to climate change.”

According to Trenberth, the atmospheric configuration that’s now preparing to dump massive snow on New England is quite reminiscent of 2010′s “Snowmageddon” — only, it’s occurring farther north. On that occasion, too, Trenberth notes, a winter storm came through at a time when the Atlantic Ocean was particularly warm — 3 degrees F warmer than normal in that case.

“That led to exceptional amounts of moisture being fed into the circulation of the storm and resulted in exceptional snow amounts in the Washington, D.C., area,” says Trenberth.

This point about atmospheric moisture is crucial. A physical equation called the Clausius-Clapeyron equation states that with warmer atmospheric temperatures, the air can hold more water vapor, setting up the chance for increased precipitation. “The atmosphere can hold four percent more moisture for every 1 F increase in temperature,” says Trenberth.

Sure enough, we’ve seen increasing trends toward extreme heavy precipitation in all regions of the United States (except Hawaii), and most of all the Northeast.
A good scientist like Dr. Trenberth will quantify such attributions as in the bolded quote.  Beware headlines or soundbites which lack such specifics; they're generally written in ignorance or have been deliberately taken out of context thereby stripping out qualifiers and other nuance.

And now for some pretty pictures ...

Noting that precipitation, and specifically snowfall, is more than just about temperature -- specific humidity being one important and oft-neglected metric -- I ginned up some animations of daily global surface temperature for all of 2014 and 2015 up to Feb. 21.

Daily Anomaly 2014:

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