The record-breaking storm that caused the Colorado floods has been called a “thousand-year event,” leading to speculation about whether the storm and flooding owed anything to climate change.
The answer, of course, is impossible to know for sure. But according to a panel of climate scientists from Colorado, the storm likely had little to do with climate change and more to do with an unusual confluence of atmospheric events.
It’s possible that some shifts due to climate change, such as increased water vapor in the air, may have exacerbated the effects of the storm slightly. But a storm in September 1938 was very similar in its footprint, its timing, and the type of rainfall (which was not the brief, intense thunderstorms typical here).
The storm was caused by a confluence of several unusual factors. A low-pressure system along the Utah-Nevada border helped pull a heavy plume of tropical moisture up from Mexico, a high-pressure system to the east pushed up even more moisture from the Gulf of Mexico, and a stalled front generated lift. All those factors set up a “blocking pattern” that helped keep the storm hovering over the same period for a long time.
Those events combining are highly unusual, said Klaus Wolter, a NOAA climate researcher who spoke at a panel discussion hosted by the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado and NOAA.
Climate change, he said, “could be a factor, but our models aren’t good enough to decide.”
Scientists agree that events like the Colorado storm “are playing out in an arena that is warmer and more moist,” says Jeff Lukas, a CIRES researcher.
But they debate the degree to which severe thunderstorms are exacerbated by human-caused global warming, though one new study published this week in the Proceedings of the National Academy of Sciences asserts that there is a definite link, and that there will likely be increased risk of such severe storms going forward if global warming continues.
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