Unlike climate change itself, there is legitimate debate on the role warmer temperatures may have played in events like Monday's tornado in Moore, Oklahoma. Was the massive storm an inevitable side effect of higher atmospheric temperatures, or was it simply a bad storm, like so many before?
What follows is a quick survey of opinions from around the web, from sources of varying respectability. We assigned the rhetorical strength of each claim judged on a scale from 0 to 400 parts-per-million of atmospheric CO2.
Sen. Sheldon Whitehouse of Rhode Island: Blame climate change
On the Senate floor Monday, Whitehouse used the storms as part of a litany of disasters for which America on the whole needs to pay. As transcribed by the Daily Caller:
Why do you care? Why do you, Sheldon Whitehouse, Democrat of Rhode Island, care if we Republicans run off the climate cliff like a bunch of proverbial lemmings and disgrace ourselves? I’ll tell you why. We’re stuck in this together. We are stuck in this together. When cyclones tear up Oklahoma and hurricanes swamp Alabama and wildfires scorch Texas, you come to us, the rest of the country, for billions of dollars to recover.
Believability: 80 ppm. Whitehouse doesn't appear to have made a strong case for the link, no matter how you feel about his argument for economic foresight.
Bill Nye the Science Guy: Blame climate change
Nye, known more for his advocacy these days than for the TV show that produced his name, took to Twitter to promote his appearance on CNN. In that tweet, he made the case.
Back to CNN midnight @piersmorganlive. Tornado 2 miles wide. More energy in the atmosphere- means more trouble.— Bill Nye (@TheScienceGuy) May 21, 2013
Believability: 300 ppm. Format of the message notwithstanding, Nye makes a key point for those who think there might be a link. The entire point of atmospheric warming is that the temperature in the atmosphere increases. And increased temperatures, you may remember from science class, means more energy, the little atoms of nitrogen and oxygen and carbon dioxide whipping around faster and faster. That energy can manifest in on-the-ground weather — though whether or not that includes tornados isn't clear.
Head of the UN's Intergovernmental Panel on Climate Change: Don't blame climate change
At least, not yet. Emphasizing the need for more data, Rajendra Pachauri expressed skepticism to reporters Tuesday.
"[O]ne really cannot relate an event of this nature to human-induced climate change. It's just not possible. Scientifically, that's not valid," he said. …
"Changes that are taking place, and that we're concerned about, include an increase in heatwaves, both in intensity and frequency, increase in extreme precipitation events and also extreme sea-level related impacts because of the increase in Arctic sea level," Pachauri said.
Believability: 300 ppm. Pachauri appears, in part, to be exercising a classic hedge against linking weather events to climate change: it's nearly always impossible to say this event couldn't have happened without increased warming. Remember the classic example of the dog going for a walk. Climate change is manifested through long-term trends more than individual events. And as The Atlantic's Alexis Madrigal noted Monday, so far there's no trend toward more or more powerful tornadoes.
Climate scientists: Maybe
The Huffington Post spoke with scientists from Princeton University and the National Oceanic and Atmospheric Administration.
The factors that contribute to tornado formation are complicated. [Princeton's Michael] Oppenheimer and other experts agree that one key ingredient, the energy-building mix of heat and humidity, will become more common as the climate warms. But ample debate remains around how climate change may affect other elements, in particular the prerequisite twisting of the wind.
Harold Brooks, a scientist with the National Oceanic and Atmospheric Administration's National Severe Storms Laboratory, suggested that lateral wind shear, which organizes storms, could actually become less favorable for tornadoes as a result of global warming. Meanwhile, Oppenheimer and Michael Mann, a climatologist who directs the Earth System Science Center at Pennsylvania State University, agreed that it's too early to tell.
Brooks also made another point: When it's too warm now, there aren't more tornadoes. During last year's heat wave, there were fewer than normal.
Believability: 380 ppm. This is precisely the sort of measured response one would expect from scientists. And as the people who study this stuff, they deserve a little more deference.
The Guardian's Harry Enten: Maybe
Enten, a reporter and statistics expert, notes that there wasn't much unusual about Monday's weather conditions.
The point is that all the normal ingredients were there that allowed an EF-4 tornado to spawn and strike. … It happened in tornado alley, where warm moist air from the Gulf of Mexico often meets dry air from the north and Rocky mountains for maximum instability. There wasn't anything shocking about this from a meteorological perspective. It was, as a well-informed friend said, a "classic" look.
Making the question: will we see more such "looks" in the future? Maybe. "[W]e'll never know whether larger global warming factors were at play in Monday's storms."
Believability: 120 ppm. Enten's analysis syncs with the science, but it's hard to assign too much weight to analysis alone.
Climate scientist Kevin Trenberth: Blame climate change (in part)
Scientific American interviewed Trenberth, who works for the National Center for Atmospheric Research. Trenberth notes that a little more warming can have a big effect on weather systems.
The climate change effect is probably only a five to 10 percent effect in terms of the instability and subsequent rainfall, but it translates into up to a 33 percent effect in terms of damage. (It is highly non-linear, for 10 percent it is 1.1 to the power of three = 1.33.) So there is a chain of events, and climate change mainly affects the first link: the basic buoyancy of the air is increased. Whether that translates into a super-cell storm and one with a tornado is largely chance weather.
But, he warns, "climate change does not change the weather or patterns of weather (much)." In other words, you might be able to blame the storm's strength on climate change, but not the storm itself.
Believability: 350 ppm. The government pays this guy to know about the climate, so we'll defer to his expertise.
American Meteorological Society president Marshall Shepherd: Don't blame climate change
Time's Bryan Walsh points to this tweet, from an exchange he had with Shepherd.
Believability: 330 ppm. Shepherd, who is also a scientist with NASA and climate science professor, is definitely in a position to have an informed opinion.
Houston Chronicle's SciGuy: Why not both?
As the SciGuy (Eric Berger) notes, we were recently talking about how few tornadoes we'd seen. Which may mean that tornadoes will be like rainfall: bigger storms and more drought.
[NOAA's Patrick] Marsh wrote: “Anyway you look at it, the recent tornado ‘surplus’ and the current tornado ‘drought’ is extremely rare. The fact that we had both of them in the span of a few years is even more so!”
Could this be related to climate change? Perhaps climate change is causing more extremes, both and high low. “The extraordinary contrast underscores the crazy fluctuations we’ve seen in Northern Hemisphere jet stream patterns during the past three years. Call it ‘Weather Whiplash’ of the tornado variety,” says Jeff Masters.
Believability: 240 ppm. It's an unusual prediction derived from experts, so make of that what you will.
Confused? Don't be. The main point is this: It's possible that climate change will result in more storms like the one that demolished Moore. It's also possible that the atmospheric energy will only manifest in exceptional droughts and massive floods. It's sort of like a Choose Your Own Adventure, in which each ending isn't one you'd choose.
Correction: An earlier version of this article misrepresented Marshall Shepherd's expertise.
Photo: A soldier walks through a devastated neighborhood. (AP)
This article is from the archive of our partner The Wire.