The relentless, weather-gone-crazy heat that has blistered the United States and other parts of the world in recent years is so rare it cannot be anything but man-made global warming, a top Nasa scientist says.
The research, by a man often called the "godfather of global warming" says the likelihood of such temperatures occurring from the 1950s through the 1980s was rarer than one in 300. Now the odds are closer to one in 10, according to the study by Professor James Hansen.
He says that statistically what is happening is not random or normal, but simply climate change. "This is not some scientific theory. We are now experiencing scientific fact," Prof Hansen said.
Prof Hansen is a scientist at Nasa's Goddard Institute for Space Studies in New York and a professor at Columbia University. But he is also a strident activist seeking government action to curb greenhouse gases.
But his study, published online in the Proceedings of the National Academy of Science, is unlikely to sway opinion among the remaining climate change sceptics, although several scientists have praised the new work.
In a blunt departure from most climate research, Prof Hansen's study - based on statistics, not the more typical climate modelling - blames these three heatwaves purely on global warming - last year's devastating Texas-Oklahoma drought; the 2010 heatwaves in Russia and the Middle East, which led to thousands of deaths; and the 2003 European heat wave blamed for tens of thousands of deaths, especially among the elderly in France.
The analysis was written before the current drought and record-breaking temperatures that have seared much of the United States this year. But Prof Hansen believes this too is another prime example of global warming at its worst.
The new research makes the case for the severity of global warming in a different way than most scientific studies and uses simple maths instead of relying on complex climate models or an understanding of atmospheric physics. It also does not bother with the usual caveats about individual weather events having numerous causes.
"This is happening often enough, over a big enough area that people can see it happening," Prof Hansen said.
Prof Hansen hopes his new study will shift people's thinking about climate change and goad governments into action. He wrote an opinion piece that appeared online in the Washington Post on Friday. saying: "There is still time to act and avoid a worsening climate, but we are wasting precious time."