Wednesday, October 17, 2018

Attribution Science Connecting Hurricane Florence to Climate Change

We can now saw with ever increasing confidence that climate change is making storms more severe and more frequent and the situation will only worsen as the planet continues to get hotter. Advances in attribution science are making it clear that climate change is fueling deadly extreme weather events.

The basic physics (the laws of thermodynamics) connecting climate change to extreme weather are well known. Warmer oceans cause more evaporation and a warmer atmosphere holds more moisture. This in turn increases rainfall and Hurricane Florence is a good example.

"Florence is yet another poster child for the human-supercharged storms that are becoming more common and destructive as the planet warms," said Jonathan Overpeck, dean of the environment school at University of Michigan.

Florence caused a record deluge. Over a four-day period there was an accumulation of nearly 36 inches of rain in places like Elizabethtown, North Carolina. This is way above the previous rain record for a hurricane anywhere on the East Coast. It broke the North Carolina record by nearly a foot. This is a once in a 1,000-year storm. To put it another way, under stable climate conditions there is  a 0.1 percent chance every year that we will see rainfall like we saw in Elizabethtown.

Georgia Tech climate scientist Kim Cobb looks at basic physics and the peer-reviewed studies that link climate change to wetter storms. "We have solid data across decades of rainfall records to nail the attribution – climate change is increasing the frequency of extreme rainfall events," Cobb said.

A Washington Post article by Christopher Mooney and Brady Dennis made the explicit connection between Hurricane Florence and climate change in their headline, "Climate change has made Hurricane Florence worse". Climate scientist Stefan Rahmstorf, a sea-level expert at the Potsdam Institute for Climate Impact Research said, "It’s a no-brainer".

Climate change is also making coastal storms more destructive due to sea-level rise. Warmer temperatures contribute to ice melt and cause the ocean to expand, this in turn increases storm surges and associated flooding.

"Essentially every coastal flood today is made deeper and more damaging by sea-level rise caused by climate change," said Benjamin Strauss, CEO and chief scientist at the research organization Climate Central

After Hurricane Matthew hit attribution science was able to make a connection. This is part of a growing wave of attribution science that is making increasingly accurate connections between a warming planet and specific extreme weather events.  Two recent independent studies have both concluded that climate change exacerbated Hurricane Harvey. A report from the World Weather Attribution consortium and Lawrence Berkeley National Laboratory found that, rainfall increased by 15 and 40 percent respectively.

Normally attribution studies take years to complete, but as reported by Grist, just before Hurricane Florence approached the Carolinas scientists published a model that tracked Florence in real time. They concluded that climate change increased rainfall associated with Florence by around 50 percent. The study was conducted by researchers from Stony Brook University in New York and Lawrence Berkeley National Laboratory in California. What makes this research so important is the fact that it is a departure from traditional studies which either report on past events or predict future one. 

A report published in the Proceedings of the National Academy of Sciences says that storms that hit Texas with more than 20 inches of rain are six times more likely now than they were at the end of the 20th century.

Even without attribution science the connection between extreme weather and climate change is pretty clear. "I think we can say that the storm is stronger, wetter and more impactful from a coastal flooding standpoint than it would have been BECAUSE of human-caused warming," Pennsylvania State University climate scientist Michael Mann wrote in an email. "And we don’t need an attribution study to tell us that in my view. We just need the laws of thermodynamics."

As quoted by the New York Times David W. Titley, a meteorologist at Pennsylvania State University, said we can expect the situation to worsen going forward. "Communities all along the Gulf Coast need to adapt to a world where the heaviest rains are more than we have ever seen," Titley said.

Updated October17, 2018, 7:30 pm EST

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