Climatide

Mercy Health / Flickr

The science linking tornado outbreaks, like those that devastated the southeast last spring, to climate change is tenuous. But, for other extreme weather events, the biggest obstacle to connecting the dots may be political, not scientific.

Extreme weather was hands-down one of the top stories of 2011, science and otherwise. With the most extreme year on record and 12 billion-plus dollar disasters in the U.S. alone, the question on many people’s minds is: is this climate change? The short answer is: in many cases, probably … or at least quite possibly. Not very satisfying, heh? I, for one, would like to know which events and how “probably.”

So what’s standing in the way? NY Times reporter Justin Gillis took a look at that question, and the answer is surprising … or maybe not. Anyway, let’s start with Gillis’ description of where the science stands, if for no other reason than I think it’s one of the strongest I’ve read.

Researchers have proved that the temperature of the earth’s surface is rising, and they are virtually certain that the human release of greenhouse gases, mainly from the burning of fossil fuels, is the major reason. For decades, they have predicted that this would lead to changes in the frequency of extreme weather events, and statistics show that has begun to happen.

For instance, scientists have long expected that a warming atmosphere would result in fewer extremes of low temperature and more extremes of high temperature. In fact, research shows that about two record highs are being set in the United States for every record low, and similar trends can be detected in other parts of the world.

Likewise, a well-understood physical law suggests that a warming atmosphere should hold more moisture. Scientists have directly measured the moisture in the air and confirmed that it is rising, supplying the fuel for heavier rains, snowfalls and other types of storms.

“We are changing the large-scale properties of the atmosphere — we know that beyond a shadow of a doubt,” said Benjamin D. Santer, a leading climate scientist who works at the Lawrence Livermore National Laboratory in California. “You can’t engage in this vast planetary experiment — warming the surface, warming the atmosphere, moistening the atmosphere — and have no impact on the frequency and duration of extreme events.”

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Call it global weirding. Call it extreme weather. Call it whatever you like, 2011 has been a record-setting weather year. So far, the U.S. alone has experienced 12 billion-dollar natural disasters, and there are still 24 days to go. Here’s the official rundown, courtesy of NOAA:

Groundhog Day blizzard » January 29-February 3, 2011

Midwest/Southeast tornadoes » April 4-5, 2011

Southeast/Midwest tornadoes » April 8-11, 2011

Midwest/Southeast tornadoes » April 14-16, 2011

Southeast/Ohio Valley/Midwest tornadoes » April 25-28, 2011

Midwest/Southeast tornadoes » May 22-27, 2011

Midwest/Southeast tornadoes and severe weather » June 18-22, 2011

Southern Plains/Southwest drought and heatwave » Spring-Fall, 2011

Mississippi River flooding » Spring-Summer, 2011

Upper Midwest flooding » Summer 2011

Hurricane Irene » August 20-29, 2011

Texas, New Mexico, Arizona wildfires » Spring-Fall 201

As it currently stands, the total toll of these twelve events is more than $54 billion in economic losses and 639 human lives lost. And, as a recent study highlighted, these figures usually don’t include the mental and physical health costs of natural disasters.

NOAA has launched an entire website dedicated to the weird, costly, and deadly weather of 2011. In an introductory statement, Jack Hayes, director of the National Weather Service, emphasized the fact that extreme weather happens every year, but seldom do we get so many events of so many different types that are so extreme.

You know, in my weather career spanning four decades, I’ve never seen a year quite like 2011. Sure, we’ve had years with extreme flooding, extreme hurricanes, extreme winter snowstorms, and even extreme tornado outbreaks. But I can’t remember a year like this in which we experienced record-breaking extremes of nearly every conceivable type of weather.

Jesse Allen / NASA Earth Observatory

The record-breaking 'snowicane' that hit Alaska earlier this month is just the latest in a string of extreme weather events in 2010 and 2011

While we’re on the subject of attribution, Climate Central has a great post on extreme weather and climate change. It includes four regional fact sheets (somehow the west coast gets ignored) listing the extreme weather events and meteorological record-breakers of 2011. The list of rainstorms, floods, snowstorms, and heat records set in the northeast alone covers three pages. And because this is Climate Central we’re dealing with, there’s also a two-page list of references to back everything up. But Climate Central also kindly provides a brief overview:

A quick summary of 2011 weather highlights would read approximately like this:  Devastating snowstorm, devastating snowstorm, blizzard, heat wave, heat wave, torrential rains, hurricane (more torrential rains), floods, hurricane remnants (even more torrential rains), worse floods, even more devastating snowstorm—and that only takes you through October.

While it’s eye-opening to see the past ten months worth of wild weather laid out in one place, it doesn’t take a fact sheet for anyone who’s lived in the northeast for any period of time to know that 2011 (and, for that matter, 2010) have been weird weather years. The question on everyone’s mind is this: Is this climate change? Here’s Climate Central’s take, in brief:

.. there’s general scientific agreement that global warming has contributed to a trend toward more intense extremes of heat and precipitation around the world, is partly to blame for specific extreme weather events over the last decade and will continue to influence both in the future.

Katkamin / Flickr

The pre-Halloween nor'easter that swept through New England last weekend dumped up to three feet of snow, downing trees still laden with green leaves and causing widespread power outages.

Was last weekend’s intense snow storm just a freak occurrence? Or a symptom of climate change? It’s a question that has been bouncing around in the wake of the storm that dumped feet of snow on parts of New England and left millions in the region without power. Few things touch us as frequently and personally as the weather, so it’s no wonder this kind of question arises whenever the weather turns unusual.

Unfortunately, a definitive answer will take time (not to mention some cutting edge science). But AP’s Seth Borenstein offered this preliminary assessment earlier this week:

The most recent bizarre weather extreme, the pre-Halloween snowstorm that crippled parts of the Northeast last weekend, cannot be blamed on climate change and probably isn’t the type of storm that will increase with global warming, according to four meteorologists and climate scientists.

Experts on extreme storms have focused more closely on the increasing number of super-heavy rainstorms, not snow, NASA climate scientist Gavin Schmidt said.

A note of caution here: scientists initially said that the Russian heatwave of 2010 was unlinked to climate change but a new study released last week found there was an 80% chance climate change was a contributing factor. So we really will just have to wait for the jury to come back.

In the meantime, here’s something we already know:

National Climatic Data Center

Data compiled by the National Climatic Data Center show that extreme one-day precipitation events have spiked in recent years.

Extreme cold season precipitation events in the northeast are definitely getting more common, as the Washington Post reported earlier this week. The graph at right tells the story pretty plainly. Historically, about 10% of weather stations in the northeast have reported extreme one-day precipitation events between October and March. But four of the last six years have seen levels above 40%. That spiked to a record-setting 77% in 2010.

Of course, it’s not just the northeast. Weather events worldwide have been hitting new extremes in recent years. There are any number of reports or statistics one could point to in support of this idea. Most recently, the Intergovernmental Panel on Climate Change (IPCC) is soon to issue a special report on extreme weather and climate change. Seth Borenstein obtained a draft copy of the report:

A draft summary of an international scientific report obtained by The Associated Press says the extremes caused by global warming could eventually grow so severe that some locations become “increasingly marginal as places to live.”

Predictions in the report include more extreme heat waves and droughts, stronger (but not more frequent) hurricanes and tropical cyclones, and more intense monsoons. By the end of the century, what have been 20-year rainstorms will likely be 5-year rainstorms, Borenstein reports. What’s more:

The draft says there is at least a 2-in-3 probability that climate extremes have already worsened because of man-made greenhouse gases.

Because of the difficulties inherent in linking any one weather event to the long-term processes of climate change, scientists are often somewhat hesitant in their public statements in this area. But there is now compelling scientific evidence (not to mention the personal experiences of millions of people) that the weather is getting more extreme – as climate scientists have long predicted it would – and that climate change is to blame.