The Link Between Deadly Weather and Global Warming Is Real -- and Conservatives Can't Just Wish It Away

When a winter blizzard buried Washington, DC, in snow early last February, global warming denialists crowed that it "proved" global warming was hokum, even as forecasters were predicting the warmest Winter Olympics ever in Vancouver, which had just recorded its warmest January ever -- seven degrees Fahrenheit hotter than normal.  

"It's going to keep snowing in DC until Al Gore cries 'uncle,'" tweeted Sen. Jim DeMint, R-South Carolina, while Fox News did a segment featuring Gore's book, An Inconventient Truth, slowly being covered by falling snow. "Sixty-three percent of the country is now covered in snow and it's breaking Al Gore's heart because the snow is also burying his global warming theory, and outside our offices, his book," chortled Eric Bolling, sitting in for Neil Cavuto on his Feb 10 show.  

Climate scientists struggled to be heard with their message that yes, global warming could actually make such extreme snowstorms more common, at the same time that average global temperatures continue to rise.  

It was a counter-intuitive argument for the man or woman on the street, but this year, the shoe's on the other foot. It's the denialists suddenly arguing that people shouldn't jump to conclusions based on the weather right in front of them, after the most deadly spate of tornadoes since the 1930s swept across the southern United States the last week in April. Questions immediately arose about whether the intense spike in the number and intensity of tornadoes could be due to global warming. It's a natural question to ask, since most of us tend to think of climate in terms of what we experience directly ourselves―which is weather. But climate scientists said the same things this year that they said last year--repeatedly telling us that climate and weather are two different things.

"Climate is what you expect. Weather is what you get," said climate scientist Brenda Ekwurzel, of the Union of Concerned Scientists. The two are intimately related, but the relationship is statistical, not causal. That doesn't make it any less real, however. 

How Climate Scientists Think About Extreme Weather 

Global warming makes certain kinds of weather events increasing more likely, but it doesn't cause them, because no one thing ever does. Think of the seasons and air temperature as an example. Summer means the air is hotter, on average. Winter means the opposite. But that doesn't automatically make a summer midnight on an Alaskan mountaintop hotter than a winter mid-day in South Florida at the beach. There are multiple factors: Season, time of day, geographical location, altitude. Still, the fact that the season/air temperature relationship is not a causal relationship doesn't lead people to ignore it―especially when planning ahead. Winter clothes may differ from place to place, but they still regularly go on sale at roughly the same time. And the first cold snap generally reminds those who have put off shopping.  When it comes to global warming, extreme weather is like that cold snap: The important thing is not whether the coming of winter “caused” it. The important thing is that it's a harbinger of what's to come. 

What's more, any store that ignored the season/air temperature relationship―on the grounds that the two aren't causally related―would quickly go out of business. Something similar is happening with global warming; the costs of ignoring the climate/weather relationship are getting harder and harder on more and more bottom lines. No clothing store ever made a killing by waiting for absolute proof it was summer before putting swimsuits on sale. 

In order to understand what is or is not happening with tornadoes and global warming, we first need to understand the broader category of extreme weather events and how climate scientists think about them. Take the example of Russia's extraordinary heat wave and drought last summer, which set the stage for vast wildfires and resulted in tremendous wheat shortages, helping to drive up world food prices. As Adam Voiland of NASA's Earth Science News Team explained in an online article, “How warm was this summer?” this was a truly unprecedented event: 

The Russian heat wave was highly unusual. Its intensity exceeded anything scientists have seen in the temperature record since widespread global temperature measurements became available in the 1880s. Indeed, a leading Russian meteorologist asserted that the country had not experienced such an intense heat wave in the last 1,000 years. And a prominent meteorologist with Weather Underground estimated such an event may occur as infrequently as once every 15,000 years. 

This was far more exceptional than the devastating tornadoes just experienced in the southern US. Yet, even with such an extreme example, climate scientists would not directly attribute it to global warming, as Voiland went on to explain:

    In the face of such a rare event, there’s much debate and discussion about whether global warming can "cause" such extreme weather events. The answer ― both no and yes ― is not a simple one. 

Weather in a given region occurs in such a complex and unstable environment, driven by such a multitude of factors, that no single weather event can be pinned solely on climate change. In that sense, it's correct to say that the Moscow heat wave was not caused by climate change. 

In short, the question “did global warming cause X extreme weather?” will always result in a negative answer, no matter what “X” may be―which can be highly misleading. It is simply the wrong question. Instead, Voiland suggested a different question, which he posed to James Hansen, director of NASA's Goddard Institute for Space Studies (GISS):

    However, if one frames the question slightly differently: "Would an event like the Moscow heat wave have occurred if carbon dioxide levels had remained at pre-industrial levels," the answer, Hansen asserts, is clear: "Almost certainly not." 

Equally illuminating is the question, “Does this extreme weather foretell the kind of climate that global warming is bringing us?” When I asked this of  Ekwurzel, she said, “I think we're already seeing it. We've already had global warming occurring since the 1950s.  We're already experiencing it, the extreme weather, and it's only going to get worse.”  

“Projected future changes in extreme weather and climate events in a warmer world are sobering,” said climate scientist Michael Wehner of Lawrence Berkeley National Laboratory in testimony submitted to Congress last year. “The cost and impacts of even small increases in the severity of these phenomena can be large. More severe heat waves, more intense precipitation events, longer and more severe drought and more intense hurricanes are all likely to be experienced in the United States as the global climate warms.” 

“We have very good evidence that the most extreme events are becoming more extreme, and that does apply to the intense flooding, the various droughts,” said  Ekwurzel, even “the area of lands that are prone to droughts are expanding.”  One the flip side, “We also know that the ice is decreasing on lake levels, and especially the ice, cryosphere, we have really, really good data that is very definitely linked to global warming.”  This bleeds into the more general well-documented evidence of global warming. “There's about ten indicators out there--snow cover lasts more than 30 days, to the warming of the lower atmosphere, the oceans, the warming of the oceans--it's so clear.” 

Extreme Storms 

Extreme storms on the one hand and heatwaves and droughts on the other are the most widespread forms of extreme weather related to global warming. People have little trouble understanding the connection with heatwaves and droughts (along with the wildfires they can spawn), but extreme storms often throw them off―as when global warming denialists pointed to heavy blizzards in the winter of 2010 as supposedly disproving global warming. However, the connection isn't hard to grasp: storms are a function of energy in the earth-sea-atmospheric system. No energy, no storms. More energy, more storms, or more commonly, more intense ones. And global warming is all about increasing the heat energy in the earth-sea-atmospheric system. A second reinforcing factor is that more heat also means more water in the atmosphere. That's why global warming really does contribute to more intense snowstorms, much to the consternation of folks like Rush Limbaugh. 

Extreme events are, almost by definition, relatively rare, and thus not the best place to look for strong scientific evidence. So the fact that they do produce such evidence ought to be more alarming. There are, for example, a growing number of studies showing increased hurricane intensity linked to global warming. These have been appearing for years now, with remarkably little notice in the corporate media, even when the timing and connections are stunning.  

For example, on July 31, 2005―a month before Hurricane Katrina devastated New Orleans―in the online edition of Nature, MIT meteorologist Kerry Emanuel reported dramatic increases in the amount of energy released in hurricanes in both the North Atlantic and the North Pacific oceans since the mid-1970s. Emanuel found that both the duration and highest wind speeds had increased by about 50 percent over the past 50 years. "My results suggest... a substantial increase in hurricane-related losses in the 21st century," he said.  

Then, shortly after Katrina, in the September 16 issue of Science, four researchers published a study showing "A large increase... in the number and proportion of hurricanes reaching categories 4 and 5," over the previous 35 years. While American attention was focused on the North Atlantic, the study found that "The largest increase occurred in the North Pacific, Indian, and Southwest Pacific Oceans, and the smallest percentage increase occurred in the North Atlantic Ocean."  

Of course, hurricanes are extremely large, relatively infrequent storms.  There may be two or more at one time near maturity in any given oceanic region during their respective hurricane seasons, but that's about it. Ordinary rainstorms are vastly more common, but evidence concerning increased rainfall in the most intense one percent of such storms is equally compelling, according to Ekwurzel. For U.S. as a whole, there's “an average of 20 percent more extreme precipitation in your heaviest one percent” of rainstorms. But the increases are most significant in two regions: “the Northeast would be 57 percent  more, and in the Midwest about 31 percent on average heavier for the heaviest rainfall,”Ekwurzel said. “So essentially, the flood risk has gone up.” 

With all this in mind, tornadoes are different from other extreme storm events in at least two main respects. First, the data for them is a good deal more sketchy than for other storms.  Rainfall data is amongst the most basic and long-recorded of any form of weather observation. Tornado data is far sketchier, though much more comprehensive than it used to be―which makes comparing recent data to that of 50 years ago a bit dodgy at best. Second, unlike other extreme storms, global warming doesn't just increase their likelihood by increasing temperature and humidity. Global warming also has an opposite effect: by heating polar regions faster than the tropics, it reduces windshear on average.   

While this dampens the relationship with global warming, it remains to be seen by how much. A 2007 modeling study lead by Anthony D. Del Genio of NASA's GISS, found that “For the central-eastern United States, stronger updrafts combined with weaker wind shear suggest little change in severe storm occurrence with warming, but the most severe storms occur more often.” 

The Challenges of Tornadoes and Modeling 

There's another challenge in studying the relationship between global warming and tornadoes: current climate models don't have the small scale resolution needed to predict tornadoes, or other severe storms on the same scale. The best that can be done is to look at preconditions, and compare those with observational data and smaller-scale high-resolution models. Still, even with these uncertainties, the future predictions are troubling.  

Jeff Trepp, of Perdue University, is the leading researcher in the field.  In 2007, he published a study which combined a a high-resolution regional climate model with a suite of global climate models. The study found “a net increase during the late 21st century in the number of days in which these severe thunderstorm environmental conditions (NDSEV) occur” with the largest increases “during the summer season, in proximity to the Gulf of Mexico and Atlantic coastal regions.”  Increases of 100 percent or more were predicted “in locations such as Atlanta, GA, and New York, NY.”  Follow-up research has strengthened the case for expecting increased tornadoes in the century ahead, but there's still a great deal of work to be done, given the uncertainties that remain. 

“The most that we can say at this point is that increases in human-induced greenhouse gasses in the atmosphere will likely lead to increases in the frequency (and intensity) of the meteorological conditions that foster severe thunderstorms,” Trapp told AlterNet. “Here, a severe thunderstorm is one that produces large hail, damaging straight-line winds, and/or tornadoes.” 

“We're limited to this conclusion on 'conditions' because our climate model simulations could not explicitly resolve thunderstorms, let alone tornadoes,” Trapp explained. “Thus, the research that we're pursing at the moment involves the use of a high-resolution (also known as "convective storm permitting) model, which is providing us information about the characteristics of individual storms, as well as how the storms form.” 

As a result, Trapp said, “This leads to the question regarding uncertainty: One of the greatest uncertainties (in addition to the basic uncertainty of the climate model) is whether or not storms will form and realize the favorable meteorological conditions.  Formation -- also known as initiation or triggering -- is often linked to weather fronts, terrain, etc., and these processes were not explicitly included in our analysis.” 

Still, for all these present limitations―similar to ones that climate researchers have overcome in the past―the picture that emerges should cause concern. “Under the climate change scenario we considered, our results did show more frequent conditions in the future for certain regions,” Trapp said. “For example, the southeast U.S. and Atlantic Coastal regions might have twice as many future days with severe thunderstorm conditions, especially during their peak season.  But again, this applies to the collective hazards of hail, wind, and tornado.” 

Confronting Doubt and Denial 

Until last month, 2008 stood out as a tornado high-point. A study headed by Trapp's Purdue colleague, Noah Diffenbaugh found that “In 2008, there were 2176 preliminary tornado reports logged through mid-December, with 1600 'actual counts' (duplicate reports removed) through September, the highest total in the past half century." But April saw over 600 tornadoes, compared to an average of 160 for the month over the past decade, according to the National Oceanic and Atmospheric Administration (NOAA). The previous one-month record was 542, in May 2003.  

But a NOAA meteorologist figured prominently in a Fox News story that rightwing climate change denialists used to attack global warming activists:  

Greg Carbin, the warning coordination meteorologist at NOAA’s Storm Prediction Center in Norman, Oklahoma, said warming trends do create more of the fuel that tornadoes require, such as moisture, but that they also deprive tornadoes of another essential ingredient: wind shear. 

“We know we have a warming going on,” Carbin told Fox News in an interview Thursday, but added: “There really is no scientific consensus or connection [between global warming and tornadic activity]….Jumping from a large-scale event like global warming to relatively small-scale events like tornadoes is a huge leap across a variety of scales.” 

Asked if climate change should be “acquitted” in a jury trial where it stood charged with responsibility for tornadoes, Carbin replied: “I would say that is the right verdict, yes.” Because there is no direct connection as yet established between the two? “That’s correct,” Carbin replied. 

“'We know we have a warming going on,' Carbin told Fox News”--and yet, Carbin was used to attack those concerned about global warming!  Hardly surprising, since the story began by contrasting his views with “environmental activists” rather than climate scientists, such as Dr. Kevin Trenberth, head of the Climate Analysis Section of the National Center for Atmospheric Research, who told Think Progress, "It is irresponsible not to mention climate change. … The environment in which all of these storms and the tornadoes are occurring has changed from human influences.”  Or Michael Mann, director of the Earth System Science Center at Pennsylvania State University, who added that “climate change is present in every single meteorological event.” 

But what about the rest of what Carbin said? 

Shaye Wolf, Climate Science Director with the Center for Biological Diversity, pointed to the work headed by Trapp and Del Genio, saying, “NOAA is ignoring a series of scientific studies that suggest a connection between rising greenhouse gas emissions and tornado activity--namely, that rising emissions are predicted to increase the frequency of conditions that spawn severe thunderstorms and tornadoes. Although scientific research is still developing, the record number of tornadoes that devastated the US this year and in recent years is consistent with studies suggesting that global warming increases the conditions that fuel tornado development.” 

Trapp himself seemed to go out of his way to minimize the conflict. “Greg's comments likely regard the observed tornado record,” he said.  “This historical record shows an increasing number of tornado reports (literally, eyewitness reports, and/or reports of damage) over the past 50 years.”  However, he warned, “The problem is that we currently don't have a way to remove the non-physical influences on these reports:  these include increases in human population and thus in population density; an improved awareness of the tornado phenomenon, and thus on tornado reporting; an organized storm spotter program, and a proliferation of amateur tornado chasers; etc.”  Such factors were discussed in the 2008 study headed by Diffenbaugh, for which Trapp was a co-author. 

Trapp went on to say that the next steps his research group has on its agenda include trying to resolve some of the uncertainty.  This involves “trying to find ways to 'bias correct' the historical record by (1) extracting tornado information from NEXRAD [doppler radar] data, and (2) using high-resolution model simulations of the current climate.”

In short, what I said in the beginning holds true: the connections between global warming and tornadoes are statistical, not causal, but altogether real nonetheless, even though there's a lot of work to be done by scientists like Trapp and his colleagues to make the picture as clear as possible.  But it's even more true that it would be foolish to wait for absolute certainty―just as it would be foolish for a store to wait for a heatwave before ordering swimsuits.  And that's a subject that deserves a lot more scrutiny than it's received so far, since it makes a mockery of the usual narratives pitting “business” against “the environment.” 

The Mounting Costs of Global Warming 

Following Hurricane Katrina, I wrote a story about global warming, hurricanes and the broader issue of the economic costs of global warming. I interviewed Gary Lemcke, a climatologist working for Swiss Re, a large re-insurance company, which is to say, a insurance company for insurance companies. He told me then that global warming was “pretty clear on our radar screen,” but “it's on a long-term perspective, ten to twenty-five years,” But that didn't mean it wasn't already a concern.  

“How long does it take to set up power lines, or build dikes? It take 10, 15, 20 years. In that sense it has an impact [now], and you see the need to educate people,” he told me. “We are in business for well over a hundred years and want to stay in business a lot longer.” 

What's more, Swiss Re was quite aware that losses from “extreme weather” did not have to involve dramatic events. Their publication, “Opportunities and Risks of Climate Change” cited a study of the unusually warm summer of 1995, which cost a total of about 1.5 billion British pounds. Thus, “even unspectacular climactic anomalies...can cause losses on a scale normally associated only with natural catastrophes,” the study warned. 

Fast forward from 2005 to 2010, and not only were reinsurance companies deeply concerned about losses from global warming, so was the SEC.  On January 27, 2010, the SEC issued what it called "Interpretive Guidance on Disclosure Related to Business or Legal Developments Regarding Climate Change".  It made no new rules or regulations, but merely clarified how its existing rules and regulations related to the issue of risks related to global warming.  Less than two months later,  Dale Wannen wrote a about the immediate impacts for Barrington Invesments, “SEC Climate Change Guidelines Lead to New Shareholder Resolutions":  

If recent talk about climate change hasn’t already rattled every CEO’s corporate cage, then yesterday’s news regarding shareholder resolutions should do the trick.  It was announced during a phone-based news conference today that investors filed a record 95 climate change resolutions against companies ranging from coal mining to big box retailers.  That’s a 40 percent increase over last year. 

He went on to explain: 

This is mostly due to the SEC’s recent guidance talk on climate change disclosure. As the SEC starts to keep a closer eye on these behemoth companies and their long-term impact on the environment, investors are clawing at an opportunity to voice themselves and have the SEC standing co-pilot.  And these investors have big money in the game. Jack Ehnes, CEO of CalSTRS [California State Teacher's Retirement System], which manages $131 billion (yes, billion) in assets says, “We want our companies to closely look at the impact climate change legislation and regulation have on them, to realistically assess those risks, and to consider the indirect consequences of climate change-driven regulation and business trends on their activities.  The SEC’s interpretive guidance outlines exactly the kind of action we have been asking our portfolio companies to take with regards to the issues raised by climate change.” 

For decades now, rightwing narratives have set the agenda for public discussions of climate change, setting up false debates, false dichotomies, and impossible levels of truth.  As climate change worsens, and extreme events make it ever harder for them to maintain their hold, they grow ever more desperate, projecting their own hysteria and denial onto others.  They are still quite powerful, as shown by the significant drop in the number of Republicans who think global warming is a real problem between 2008 and now.  But in the long run, Mother Nature bats last, and she doesn't just change the physical environment, she changes the business environment as well.  And that's precisely what's begun to happen, even if it's not dominating headlines yet. 

“Our study adds to the list of related studies that do indeed suggest increases in the extremes, which includes droughts, floods, and damaging thunderstorms,” Trapp said. “Knowing the possible impact of the high-end events -- or a high-end month like April 2011 -- will help in adaptation measures and other long-term planning.”   

Regardless of what global warming denialists may say, more and more people are now listening to what scientists like Trapp have to say―including those with a lot to lose in the world of business if they don't start paying attention.   


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