by Judith Curry
I’ve been pretty clear about where I stand with regards to the attribution of extreme events to global warming, e.g. see this thread. The recent tornado outbreak in the southeast U.S. has spawned a number of statements and articles about the cause of the outbreak including, inevitably, global warming.
Why am I not surprised?
• Peter Gleick on the Huffington Post: A cost of denying climate change
Violent tornadoes throughout the southeastern U.S. must be a front-page reminder that no matter how successful climate deniers are in confusing the public or delaying action on climate change in Congress or globally, the science is clear: Our climate is worsening.
• ThinkProgress: Storms Kill Over 250 Americans in States Represented by Climate Pollution Deniers.
The title speaks for itself on this one
• From the WonkRoom: words from Trenberth, Mann and Schmidt.
Dr. Kevin Trenberth, one of the world’s top climate scientists, who has been exploring for years how greenhouse pollution influences extreme weather, said he believes that it is “irresponsible not to mention climate change” in the context of these extreme tornadoes.
Michael Mann: The fact remains that there is 4 percent more water vapor–and associated additional moist energy–available both to power individual storms and to produce intense rainfall from them. Climate change is present in every single meteorological event, in that these events are occurring within a baseline atmospheric environment that has shifted in favor of more intense weather events.
Gavin Schmidt: It is a truism to say that everything has been affected by climate change so far and therefore this latest outbreak must in some sense have been affected, but attribution is hard and the further down the chain the causality is supposed to go, the harder this is. For heat waves it is easier, for statistics on precipitation intensity it easier – there are multiple levels of good modelling, theory and observations to back it up. But we have much less to go on with tornadoes. JC comment: actually this one belongs in the “cooler heads” category, kudos to Gavin
• From NOAA, a historical perspective.
• Washington Times: Tornadoes Spinning Global Warming
The case linking tornadoes to global warming is even sketchier, and the science is far from “settled.” A 2007 NASA study predicted that the number of tornadoes would increase with global warming. A 2009 study by University of Georgia found the opposite. The number of recorded tornadoes has risen in the last 20 years, but the rise coincides with greater use of Doppler radar and other advanced means of detecting tornadic activity, creating an acute issue of data artifice. A definitive answer to the question may not be possible. Given this lack of proof, the alarmists are forced to fall back on the question “what if?”
• Newsbusters: includes comments from Greg Forbes:
Yeah, it really has been a remarkable April, certainly a record April. It may be the most tornadic month of any month on record. It certainly, the atmosphere has been in a frenzy. The jet stream just keeps blasting across the country, and then the warm moist air from the Gulf of Mexico just keeps feeding the instability and so we’ve had tornado after tornado…
• Fox News: Interview with Greg Carbin:
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.
• Time: Tornadoes, Climate Change, and the Disaster Gap
A 2009 study by University of Georgia researchers suggested that drier autumns and winters that might be seen due to warming could actually lead to fewer tornadoes developing during the spring season, at least in the Southeast, though the scientists cautioned that their data was preliminary. A research project by Michael Pateman and Drew Vankat found that the frequency of tornadoes had increased between 1950 and 1999—though better detection likely played a significant role in those statistics. But if there’s strong evidence that climate change and tornadoes are connected, researchers have yet to uncover it—and given how difficult and time-consuming it is to attribute a weather event to warming, don’t expect a firm conclusion soon.
• Physorg.com: Tornadoes whipped up by wind, not climate
Violent twisters that famously rip through the US south’s “Tornado Alley” are formed when strong jet winds bringing upper-level storms from the north interact with very warm, humid air mass from the Gulf of Mexico, said David Imy from the NOAA Storm Prediction Center in Norma, Oklahoma.
On Wednesday, a particularly potent storm was whipping up around the heart of that tornado-prone corridor where the states of Arkansas, Oklahoma, eastern Texas and northwest Louisiana meet, noted Kristina Pydynowski, a seniormeteorologist at the AccuWeather.com website.
Sparking the severe thunderstorms from that point was the much warmer air arriving from the south, over the tropical Gulf. The combining winds at differing altitudes, said Pydynowski, created “significant twisting motion in the atmosphere, allowing the strongest thunderstorms to spawn tornadoes.”
• Climate Central: Tornado Outbreak Raises Climate Questions
Those of us who write about climate change are often accused of attempting to link every unusual weather event to climate change, as if increasing air and ocean temperatures can explain everything from hurricanes to snowstorms. In this case, with the worst tornado outbreak since at least the 1974 “Super Outbreak”, and with the most tornadoes for any April since records began in the early 1950s, it’s important to understand that the scientific evidence indicates that climate change probably played a very small role, if any, in stirring up this violent weather. This might disappoint some advocates who are already using this to highlight the risks of climate change-related extreme weather.
• Mike Smith of Meteorological Musings, has a number of interesting and relevant posts on meteorology of this outbreak: