As hurricane Irene blasted up the eastern seaboard in August, it left record damage in its wake. Rivers in 10 states reached all-time highs, and communities suffered devastating floods. In all, it made 2011 the worst year, in terms of economic damage, from weather/蜜柚APP disasters in the past 31 years. Yet Irene’s severity wasn’t exactly unexpected. Intense Atlantic hurricanes have been growing in number since the 1970s. Heat waves have become more common since the 1950s and droughts more widespread. And this summer was the second warmest in recorded history, after only 1936.The public has begun to suspect that the severe weather is due to human-caused 蜜柚APP change and to wonder whether it will be the norm in a warmer world. Rising atmospheric greenhouse-gas concentrations trap heat in the air, causing surface temperatures to rise. A warmer atmosphere holds more water vapor, likely leading to heavier rain events and worse flooding and drought in some areas. That all sounds like...