A new NASA study has found that extreme heat events are far more likely to occur than five decades ago, a phenomenon that researchers link to climate change. In an analysis of long-term statistical trends, a team of researchers led by James Hansen of NASA’s Goddard Institute for Space Studies describes how “extremely hot” summers — defined as abnormally high mean summer temperatures that affected less than 1 percent of the planet’s land area between 1951 and 1980 — have become far more routine in the last three decades. According to their analysis, published in the Proceedings of the National Academy of Sciences, about 10 percent of land areas in the Northern Hemisphere have experienced such temperatures since 2006. And while the chances of experiencing extreme heat events from the 1950s to the 1980s were less than 1 in 300, the odds now are closer to 1 in 10. “This is not some scientific theory,” Hansen told the Associated Press. “We are now experiencing scientific fact.” The shifting trend, he said, was behind last year’s Texas drought and the 2010 Russian heat wave. This summer, Hansen said, is also shaping up to fit into the new “extreme” category.