龙卷风的强度频率与气候变化

New research by a Florida State University geography professor shows that climate change may be playing a key role in the strength and frequency of tornadoes² hitting the United States. Published Wednesday in the journal Climate Dynamics³, Professor James Elsner writes that though tornadoes are forming fewer days per year, they are forming at a greater density⁴ and strength than ever before. So, for example, instead of one or two forming on a given day in an area, there might be three or four occurring.   "We may be less threatened by tornadoes on a day-to-day basis, but when they do come, they come like there's no tomorrow," Elsner said.   Elsner, an expert in climate and weather trends, said in the past, many researchers dismissed the impact of climate change on tornadoes because there was no distinct pattern in the number of tornado¹ days per year. In 1971, there were 187 tornado days, but in 2013 there were only 79 days with tornadoes.   But a deeper dive into the data showed more severity in the types of storms and that more were happening on a given day than in previous years.   "I think it's important for forecasters and the public to know this," Elsner said. "It's a matter of making sure the public is aware that if there is a higher risk of a storm, there may actually be multiple storms in a day."   The United States experiences more tornadoes than any other country, and despite advances in technology and warning systems, they still remain a hazard to residents in storm-prone areas. The 2011 tornado season, for example, had nearly 1,700 storms and killed more than 550 people.   So far, in 2014, there have been 189 storms with a death toll⁵ of 43, according to the NOAA/National Weather Service Storm Prediction Center.   One bright spot of news in the research, Elsner added, was that the geographic⁶ areas impacted most regularly by tornadoes do not appear to be growing.   Elsner was joined on the paper by independent researcher Thomas H. Jagger, formerly⁷ a research associate at Florida State University, and meteorologist（气象学者） Svetoslava Elsner.