SAN FRANCISCO, CA, DECEMBER 15, 2015 — “Dangerous climate change is already here,” scientist Don Wuebbles told one of the flagship presentation venues at the Fall Meeting of the American Geophysical Union.
“Certain types of extreme events are becoming more common,” he added, “a trend likely to continue.”
Wuebbles, an atmospheric scientist at the University of Illinois in Champaign-Urbana, gave the Stephen H. Schneider Lecture, honoring the late Stanford scientist who was a leader in both doing and communicating climate science, while zestfully battling back against critics, skeptics, and lymphoma. Schneider died in 2010.
From 1980 to 2013 there were 151 extreme weather events in the United States that exceeded $1 billion in cost. The cost trend depends on population, wealth and inflation, but Wuebbles also showed a graph from the reinsurance company Munich Re showing that extreme events are increasing in number, too (see figure).
There is high confidence, Wuebbles said, that the risk of extreme cold weather is decreasing, and the frequency of extreme heat events increasing.
But there is only medium confidence that global warming will lead to more intense middle-latitude hurricanes, such as those that strike the U.S. east coast. And “the jury is still out,” Wuebbles said, on an increased risk of more extreme winters, changes in hurricane frequency, and changes in tornadic activity.
“For 2 degrees C of global warming [3.6 degrees F], the hottest days will be 2-5 degrees C [3.6-9 degrees F] warmer than pre-industrial levels.”
Wuebbles also noted an upward trend in extreme precipitation events in the U.S., with what were once one-in-five year heavy rain events now happening every 3.7 years on average. He said there is inadequate data to determine trends in severe thunderstorms.
With his students, Wuebbles is studying teleconnections – long-distance correlations – between the Arctic and the mid-latitudes that the U.S. occupies. In a phrase that’s been heard often at this AGU meeting, Wuebbles said, “What happens in the Arctic does not stay in the Arctic,” a play on the phrase popularized by TV commercials supporting Las Vegas tourism.
In particular, “sea ice is now a mere shadow of its former self,” said Wuebbles, adding that half of summer sea ice extent is now gone, and 75 percent of sea ice volume. “And what’s left is rotten and slushy.”
There have been prominent debates in the last few years among scientists on whether Arctic amplification is changing the jet stream and its waviness, and implications for the U.S. In Wuebbles’s work, any hypothetical teleconnections must take into account El Ninos and La Ninas, longer-term ocean cycles like the Pacific Decadal Oscillation, and other complications, and he said his results so far lack clear specificity.
An expert in numerical modeling of atmospheric physics and chemistry, Wuebbles has been a coordinating lead author on a IPCC assessment report and a U.S. National Climate Assessment, and has won numerous awards for his work.
During the period for questions, Wuebbles noted that climate models “tend to not find as much extreme weather as is happening.” Asked, by a member of Bill McKibben’s organization 350.org, about McKibben’s post-Paris op-ed in the New York Times – where McKibben attributed to the warming climate landslides in Washington state to climate change, and the rainiest December in the records in Portland, Oregon, and the worst flooding Norway has seen in a decade – Wuebbles said “there’s no question about the changing trends we’re observing and projecting,” but that “attributing a large hurricane event, say, is going too far.”
Wuebbles closed by answering another question on whether global observing networks were declining in quality, saying “this is a very serious concern.”
“We are losing capabilities we have now. We [scientists] are going to have to push very hard on this.”