White House science adviser John Holdren is pushing back against conservatives who claim the U.S. cold snap shows that global warming isn't real.
"If you have been hearing that extreme cold spells, like the one that we are having in the United States now, disprove global warming, don't believe it," Holdren said in a video the White House circulated Wednesday.
In fact, he notes, "a growing body of evidence" suggests that the type of extreme cold the U.S. is experiencing could become more frequent as global warming continues.
The former Harvard University professor's short video arrives as conservatives who deny human-induced climate change are seizing on the cold snap.
Rush Limbaugh claimed this week that the "polar vortex"—the Arctic cold-air mass that's invaded the U.S.—is a left-wing and media invention to link the cold snap to the "global warming agenda."
And on the Senate floor this week, Sen. James Inhofe, R-Okla., cited the cold weather to support his claims that global warming is a hoax.
Inhofe's views are counter to the overwhelming majority of scientists who say human activities are a driving force behind rising global temperatures.
Holdren said, "No single weather episode can either prove or disprove global climate change."
But Holdren offered a brief lesson on how global warming could be fueling this week's frigid temperatures by affecting the polar vortex, which he noted is the swirling mass of cold air that hovers around the North Pole.
He said the Arctic is warming roughly twice as fast as mid-latitude areas like the U.S., so the temperature difference between the regions is shrinking. That's weakening the vortex and making it "wavier."
"The waviness means that there can be increased, larger excursions of cold air southward, that is, into the mid-latitudes, and in the other phase of the wave, increased excursions of relatively warmer, mid-latitude air into the north," Holdren said.
The White House is also hosting an online event Friday with climate scientists and other experts about the cold snap, extreme weather, and climate change.