What's the Latest Development?

America, 2012; Texas, 2011; Russia, 2010; Europe, 2003. These are the heat waves and droughts that scientists now say were directly caused by global warming, itself a result of greenhouse gases produced by human activity. Published Monday in the Proceedings of the National Academy of Sciences, the new study "compared the global climate of 1951 to 1980, before the bulk of global warming had occurred, with the climate of the years 1981 to 2011." In the first era, 0.2% of the globe's surface suffered extreme summer heat. In the second, extreme heat covered 4 to 13% of the world. 

What's the Big Idea?

Authors of the study, including one of NASA’s principal climate scientists, James Hansen, say the data show that temperature increases since 1980 go beyond the scope of natural climate variability. Despite difficulties with pinpointing the cause of specific weather events such as heat waves and droughts, "scientists have long believed that the warming—roughly 2.5 degrees Fahrenheit over land in the past century, with most of that occurring since 1980—was caused largely by the human release of greenhouse gases from burning fossil fuels." In an interview, Dr. Hansen said: "It confirms people’s suspicions that things are happening. It's just going to get worse."

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