Tornadoes have killed more people this year than they have since 1953. This has some wondering whether higher global temperatures might be contributing. The answer: there isn’t a statistical correlation between the number of tornadoes and rising temperatures. Yet scientists predict that climate change will bring increasingly harsh weather, and that’s got some commentators wondering whether this year’s tornadoes, record floods, and droughts, might be connected.
“This year is an extraordinary outlier,” said Harold Brooks, research meteorologist at the National Oceanic and Atmospheric Administration’s (NOAA) National Severe Storms Laboratory in Norman, Oklahoma… . But when scientists examine the most complete records available and adjust for changes in how tornadoes were reported over time, “we see no correlation between global or US national temperature and tornado occurrence,” Brooks said.
From New York Times:
Over all, the number of violent tornadoes has been declining in the United States, even as temperatures have increased, making it likely that this year’s twister outbreak is simply a remarkable and terrifying — but natural — event.
Climate science has long predicted that global warming will cause more weather extremes, however, and statistics suggest this has started to happen. In most areas of the world where good weather data is available, instances of heavy precipitation are rising, often leading to flash flooding. And the same thing is true of heat waves; in the United States, new high-temperature records for a given date now occur twice as often as record lows.
That said, scientists are reluctant to attribute any specific weather event to global warming.
Warmer temperatures and more moisture will give storm systems that much more energy to play with, like adding nitroglycerin to the atmosphere. This month’s possibly record-breaking tornadoes are due in part to an unusually warm Gulf of Mexico, where as Freedman reports, water surface temperatures are 1 to 2.5 C above the norm. The Gulf feeds moisture northward to storm systems as they move across the country, and that warm moist air from the south meeting cool, dry air from the Plains often results in some powerful weather. But at the same time, other studies have forecast that warmer temperatures will reduce the wind shear necessary to turn a routine thunderstorm into a powerful system that can give birth to tornadoes. So in a hotter world we could see more frequent destructive thunderstorms, but fewer tornadoes—although some researchers think we could still end up with both.
Then there’s this sarcastic editorial from climate activist Bill McKibben:
Caution: It is vitally important not to make connections. When you see pictures of rubble like this week’s shots from Joplin, Mo., you should not wonder: Is this somehow related to the tornado outbreak three weeks ago in Tuscaloosa, Ala., or the enormous outbreak a couple of weeks before that (which, together, comprised the most active April for tornadoes in U.S. history). No, that doesn’t mean a thing.
It is far better to think of these as isolated, unpredictable, discrete events. It is not advisable to try to connect them in your mind with, say, the fires burning across Texas — fires that have burned more of America at this point this year than any wildfires have in previous years. Texas, and adjoining parts of Oklahoma and New Mexico, are drier than they’ve ever been — the drought is worse than that of the Dust Bowl. But do not wonder if they’re somehow connected …
It’s far smarter to repeat to yourself the comforting mantra that no single weather event can ever be directly tied to climate change. There have been tornadoes before, and floods — that’s the important thing. Just be careful to make sure you don’t let yourself wonder why all these record-breaking events are happening in such proximity — that is, why there have been unprecedented megafloods in Australia, New Zealand and Pakistan in the past year. Why it’s just now that the Arctic has melted for the first time in thousands of years.