WASHINGTON — Humans are largely to blame for the recent trend toward more powerful hurricanes, a group of 19 American and European scientists declared Monday. In a paper appearing in the Proceedings of the National Academy of Sciences, the scientists claim to have established a solid chain linking human burning of fossil fuels, global warming, higher ocean temperatures, and the intensity and duration of recent hurricanes such as Katrina and Wilma. The scientists’ key finding was that as sea surface temperatures rise and fall, the maximum wind speed of hurricanes goes up and down in step with them. ‘Human-caused changes in greenhouse gases are the main driver’ of warmer waters in the tropical Atlantic and northwestern Pacific oceans, where hurricanes and cyclones are born, the paper says. Its principal author was Benjamin Santer, a senior climate researcher at Lawrence Livermore National Laboratory in Livermore, Calif. Other contributors come from 11 different laboratories in the United States, Germany and England. Their report is unlikely to end the controversy over the connection between human burning of fossil fuels in cars, buildings and factories, the warming of the world’s air and seas, and the surge in category 4 […]