Severe flooding during Hurricane Florence has provided new evidence that accumulating heat in the world’s oceans from climate change is bringing new dangers to the nation’s coastlines.
Rising ocean energy is closely connected to the growing size of storms, the intensity of their rains and the resulting flood damage, according to scientists.
Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., says Florence’s power underscores new research that suggests storms are being “supercharged” by rising temperatures and that states and the federal government should do more to prepare for them.
Florence, a huge, slow-moving storm carrying a heavy load of precipitation, “could have brought as much as 50 percent more rainfall than if it occurred 100 years ago,” Trenberth said in an interview.
Trenberth is the lead author of a study linking ocean heat to Hurricane Harvey’s flooding of Houston last year with 60-inch rains. He says the research draws on data from a network of 3,000 devices called “Argo floats,” drone-like underwater sensors that can move up and down in the water and are now measuring the ocean’s heat and salinity levels around the world (Climatewire, Jan. 11).
By 1985, scientists became aware that oceans are storing over 92 percent of the rising global heat from greenhouse gases such as carbon dioxide—man-made emissions that tend to block the reflection of solar heat back into space. But researchers could only measure sea surface temperatures by satellites until the Argo system began operating in 2005. The program is supported by the United States and other nations.
The Argo system showed that seawater temperatures were also rising at depths as far down as 525 feet. Trenberth’s study, which had four other authors, showed that the heat in the ocean areas feeding Hurricane Harvey caused evaporation and resulted in more airborne moisture. That expanded the size of the storm, giving it the energy to dump more rain over a large area while continuing to draw moisture from the ocean.
Hurricane Irma, which raked Florida last year, also broke a number of records, including the longest Category 5 storm. It was “unprecedented in the way it straddled Florida affecting the whole peninsula as it moved northward,” the study noted.
After these storms ended, the oceans that fed them cooled. The area that fueled Harvey had a net energy loss that the scientists found roughly equaled the mounting strength of the storm. According to Trenberth, the lingering cooling may have reduced the potential for storms near the Gulf of Mexico this year. While sea surfaces can reheat quickly, it can take weeks or months for deeper water to heat up.
“If you map the path of hurricanes, you will see that they never go along the same tracks, so I think that these cold wakes have quite an influence,” Trenberth explained. He added that Florence followed an unusual track across the Atlantic, which had some of the warmest spots this year. That might have increased evaporation and fueled the storm as it plodded toward the Carolinas.
The water was also exceptionally warm this year in the Hawaiian Islands, he noted, which are usually too far north to experience tropical storms. One result was two hurricanes.
Trenberth, who has been studying the relationships between rainfall and climate change since 1998, said wind speeds and storm surges of hurricanes can vary, according to quirks in the weather and local tides, but the rain from such a storm can extend as far as 1,000 miles.
“That’s the most widespread risk,” he said.
He thinks cities near the coasts may need more space to store water to avoid some of the massive damages that come with flooding.
“Managing water is one of the key challenges when it comes to climate change,” Trenberth said.
Another challenge is to develop better climate models to show changing extremes of storms instead of relying on global statistical averages, which tend to lag behind the changes that are underway.
Lately, insurance companies have been consulting with Trenberth.
“They’re very concerned,” he said. “The big topic of their work is trying to make sure they have an appropriate level of risk accounted for. One of their issues is that local politicians won’t let them charge what the risks require. People are still building on barrier islands and other places where they ought not to. And some companies won’t insure these projects anymore.”
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.