Intenser, wetter, windier storms in a warming world

 From  Inside Climate News

The federal government counts 52 tropical cyclones since 1980 that, with the cost adjusted for inflation, have caused, on average, $20 billion in damages in the United States. There were a record seven so-called “billion dollar” cyclones just last year.

With climate change helping produce a global horror film of extreme weather disasters this summer, and the peak Atlantic hurricane and Western fire seasons just arriving, a new landmark United Nations climate report by the Intergovernmental Panel On Climate Change offers the most thorough evaluation of the physical science associated with global warming so far, including the climate science of tropical cyclones.

Made public Monday, the IPCC report was written by 234 scientists from 66 countries and approved by 195 member governments of the IPCC.

To meteorologists, tropical cyclones are rotating, organized systems of clouds and thunderstorms that originate over tropical or subtropical waters. In the North Atlantic, central North Pacific and eastern North Pacific they are called hurricanes once wind speeds reach 74 miles per hour. Major hurricanes, categories 3 to 5, pack wind speeds of 111 miles per hour to more than 157 miles per hour, and cause damage that ranges from devastating to catastrophic.

The IPCC authors did not do original research for their report. Rather, they assessed the state of knowledge and the confidence in it based on previously published scientific reports.

Hugh Willoughby, a professor at Florida International University in the Department of Earth and Environment who has been studying hurricanes for decades, said the IPCC report’s assessment of hurricanes reveals an unsurprising picture of evolving science.

“It is consistent with what we have thought for 40 years,” said Willoughby, who flew more than 400 missions into hurricanes as a meteorologist with the federal government and led the National Oceanic and Atmospheric Administration’s Hurricane Research Center from 1995 to 2002. “What is new is more and more (hurricane) events that fit the pattern, and that is what you would expect.” 

To determine six, key takeaways about tropical cyclones and climate change from the IPCC report, Inside Climate News interviewed Willoughby and two academic researchers whose work was cited by the report’s authors: Colin Zarzycki, an assistant professor of meteorology and climate dynamics at Pennsylvania State University and Phil Klotzbach, a hurricane expert and research scientist at Colorado State University’s Department of Atmospheric Science.

• More Major Tropical Cyclones. It is likely, the report found, that the percentage of major tropical cyclones—those reaching categories 3 to 5—increased over the last four decades. Scientists are confident in saying that there will be more frequent storms in the highest intensity categories of 4 and 5.
• Wetter, Windier Tropical Storms. Warmer air holds more moisture, and human-driven climate change is making tropical cyclones wetter. The authors found that, generally, storms with extreme daily precipitation are projected to intensify by about 7 percent for each 1 degree Celsius of global temperature warming. The authors also expressed high confidence in projections that peak wind speeds in the most intense tropical cyclones—categories 4 and 5—will increase with increasing global warming.

• Tropical Storms are Shifting North. In the North Pacific, tropical cyclones are reaching their maximum intensity farther north than before, potentially exposing areas that have no experience with tropical cyclones to a risk of dealing with them in the future. The report said this is partly explained by changes in global-scale tropical atmospheric circulation. 
• More Explosive Tropical Cyclones. With warmer sea-surface temperatures, the frequency of storms that rapidly intensify has increased.
• Slower [Moving] Tropical Cyclones that Can Do More Damage. When slower moving cyclones make landfall, they can drop more rain, cause more wind damage and sustain a larger storm surge simply because they hang around longer. The IPCC authors cited research in 2019 that provided evidence that translation speed for Atlantic storms decreased 17 percent from 1900 to 2017. In addition, what scientists call “meanders” and “stalls” in tropical cyclone paths have become increasingly common, along with the slower speeds.

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Hurricane Harvey struck the Texas coast in August 2017. Credit: NOAA