Tornadoes and Climate Change

Cross-posted from NextGen Journal

It has been a bad season for tornadoes in the United States. In fact, this April shattered the previous record for the most tornadoes ever. Even though the count isn’t finalized yet, nobody doubts that it will come out on top:

In a warming world, many questions are common, and quite reasonable. Is this a sign of climate change? Will we experience more, or stronger, tornadoes as the planet warms further?

In fact, these are very difficult questions to answer. First of all, attributing a specific weather event, or even a series of weather events, to a change in the climate is extremely difficult. Scientists can do statistical analysis to estimate the probability of the event with and without the extra energy available in a warming world, but this kind of study takes years. Even so, nobody can say for certain whether an event wasn’t just a fluke. The recent tornadoes very well might have been caused by climate change, but they also might have happened anyway.

Will tornadoes become more common in the future, as global warming progresses? Tornado formation is complicated, and forecasting them requires an awful lot of calculations. Many processes in the climate system are this way, so scientists simulate them using computer models, which can do detailed calculations at an increasingly impressive speed.

However, individual tornadoes are relatively small compared to other kinds of storms, such as hurricanes or regular rainstorms. They are, in fact, smaller than a single square in the highest-resolution climate models around today. Therefore, it’s just not possible to directly project them using mathematical models.

However, we can project the conditions necessary for tornadoes to form. They don’t always lead to a tornado, but they make one more likely. Two main factors exist: high wind shear and high convective available potential energy (CAPE). Climate change is making the atmosphere warmer, and increasing specific humidity (but not relative humidity): both of these contribute to CAPE, so that factor will increase the likelihood of conditions favourable to tornadoes. However, climate change warms the poles faster than the equator, which will decrease the temperature difference between them, subsequently lowering wind shear. That will make tornadoes less likely (Diffenbaugh et al, 2008). Which factor will win out? Is there another factor involved that climate change could impact? Will we get more tornadoes in some areas and less in others? Will we get weaker tornadoes or stronger tornadoes? It’s very difficult to tell.

In 2007, NASA scientists used a climate model to project changes in severe storms, including tornadoes. (Remember, even though an individual tornado can’t be represented on a model, the conditions likely to cause a tornado can.) They predicted that the future will bring fewer storms overall, but that the ones that do form will be stronger. A plausible solution to the question, although not a very comforting one.

With uncertain knowledge, how should we approach this issue? Should we focus on the comforting possibility that the devastation in the United States might have nothing to do with our species’ actions? Or should we acknowledge that we might bear responsibility? Dr. Kevin Trenberth, a top climate scientist at the National Center for Atmospheric Research (NCAR), thinks that ignoring this possibility until it’s proven is a bad idea. “It’s irresponsible not to mention climate change,” he writes.

What Kevin Trenberth Has to Say

A comment from Steve Bloom several months ago got me thinking about a new kind of post that would be a lot of fun: interviewing top climate scientists, both on their research and their views of climate science journalism and communication. When I emailed Dr. Kevin Trenberth to see if he would be interested in such an interview, he responded with an entire essay that he had written about recent events in climate change communication. Although this essay is unpublished as of yet, he graciously suggested that I quote it for a post here.

It’s no surprise that Dr. Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Colorado, is angry about the way stolen emails between researchers were trumpeted around the world in an attempt to make them seem like something they were not. He was “involved in just over 100” of the emails, and from the looks of things, hasn’t heard the end of it since they were stolen.

One oft-quoted statement of his went viral: The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t. Climate change deniers portrayed this quote as an admission that the world wasn’t warming after all, or even that scientists were trying to cover up a cooling trend. Taken in the full context of the email in which it was written, however, it’s clear that Trenberth was referring to a recent paper of his, which discussed our incomplete understanding of the factors affecting short-term variability in the Earth’s temperature. There were a couple years between 2004 and 2008 that weren’t quite as warm as scientists expected after looking at all the forcings, such as solar irradiance and ENSO. The paper and the subsequent email in no way mean that global warming has stopped. In fact, we’re well on our way to the warmest year on record. “It is amazing to see this particular quote lambasted so often,” says Trenberth.

Another quote, this time from a stolen email he was not even a recipient of, was written by Phil Jones, the director of CRU. I can’t see either of these papers being in the next IPCC report, wrote Jones, referring to several studies that were not regarded very highly by the climate science community, one of which was later retracted. Kevin and I will keep them out somehow – even if we have to redefine what the peer-reviewed literature is!

Dr. Trenberth offers an insight for this comment that was previously unknown to me. The IPCC’s 2007 report “was the first time Jones was on the writing team of an IPCC Assessment,” he says. “The comment was naive and sent before he understood the process and before any lead author meetings were held…As a veteran of 3 previous IPCC assessments, I was well aware that we do not keep any papers out, and none were kept out.” Indeed, both studies were discussed in the 2007 report, offering proof that the private emails of scientists do not always correspond to their ultimate actions.

To date, four independent investigations (five if you count the two Penn State reports as separate) “have confirmed what climate scientists have never seriously doubted: established scientists depend on their credibility and have no motivation in purposely misleading the public and their colleagues.” Referring to the only major criticism that the investigations had for CRU, Trenberth notes that scientists “are also understandably, but inadvisably, reluctant to share complex data sets with non-experts that they perceive as charlatans.”

Despite the complete absence of evidence for scientific fraud, the fact that no papers were changed or retracted due to these emails, and the obvious innocence of scientists like Dr. Trenberth, public confusion over climate change has grown in recent months. Almost everyone who keeps up with the news will remember hearing something about climate researchers accused of malpractice. “There should be condemnation of the abuse, misuse and downright lies about the emails,” says Trenberth. “That should be the real ClimateGate!”

After all this experience as the subject of libelous attacks and campaigns of misinformation, Kevin Trenberth can offer suggestions for other scientists in the same position. He does not recommend debating the conclusions of climate change research in the public sphere, as “scientific facts are not open to debate and opinion because they are evidence and/or physically based.” He has learned, like so many of us here at ClimateSight, that “in a debate it is impossible to counter lies [and] loudly proclaimed confident statements that often have little or no basis.”

“Moreover,” he adds, “a debate actually gives alternative views credibility,” something that climate change deniers haven’t earned. He and his colleagues “find it disturbing that blogs by uninformed members of the public are given equal weight with carefully researched information backed up with extensive observational facts and physical understanding.”

Much of the online climate change community has lost faith with climate journalism in recent months, and Dr. Trenberth is no exception. He asserts that the mass media has been “complicit in this disinformation campaign of the deniers”, and has some explanations as to why. “Climate varies slowly,” he says, “and so the message remains similar, year after year — something not exciting for journalists as it is not “news”.” He also notes the stubborn phenomenon of artificial balance, as “controversy is the fodder of the media, not truth, and so the media amplify the view that there are two sides and give unwarranted attention to views of a small minority or those with vested interests or ideologies.”

“The media are a part of the problem,” says Trenberth. “But they have to be part of the solution.”