James E. Hansen, head of the NASA Goddard Institute for Space Studies, declared Aug. 3 that a new study by him and colleagues Makiko Sato and Reto Ruedy proves global warming is causing the extreme weather dominating the news in recent years. The study was published today online in the (NAS). Hansen asserts in an op-ed for , that “for the extreme hot weather of the recent past, there is virtually no explanation other than climate change.”

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Hansen is famous for his 1988 congressional testimony declaring that human-caused global warming had begun. That testimony, along with Hansen’s projections that greenhouse gases (GHGs) would cause further temperature increases, helped propel climate change into public consciousness and policy debate. Hansen now says his projections about increasing temperatures “have been proved true” but that, in fact, he “failed to fully explore how quickly that average rise would drive an increase in extreme weather.”

It’s been common up to now for climate scientists to state that rising temperatures “load the dice” or change the odds so that extreme weather is more likely. For example, a July study from the National Oceanic and Atmospheric Agency (NOAA) found that “Cold Decembers are half as likely to occur now versus fifty years ago, whereas warm Novembers are now 62 times more likely.”

But the new study goes further than that. The researchers charted the world’s changing temperatures over the past 30 years and found that “the extremes of unusually cool and, even more, the extremes of unusually hot are being altered so they are becoming both more common and more severe,” Hansen writes. Extreme-heat events, Hansen says, “used to be exceedingly rare.” But the study identifies a new category of events that it calls “summertime extremely hot outliers.” The researchers write that “This hot extreme, which covered much less than 1 percent of Earth’s surface during the base period [1951-1980], now typically covers about 10 percent of the land area.”

Climate scientists are usually hesitant to connect any one weather event with climate change. But the new study gets more direct, stating that:

It follows that we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming because their likelihood in the absence of global warming was exceedingly small.

In his essay Hansen says that new analysis shows that such events “will become even more frequent and more severe.” Hansen, who is not just a scientist but also an environmental activist, believes the climate change problem can be fought by imposing “a gradually rising fee on carbon collected from fossil-fuel companies, with 100 percent of the money rebated to all legal residents on a per capita basis.” Such a measure would “stimulate innovations and create a robust clean-energy economy.”

+ Perception of Climate Change Study

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Chart credit: NASA

Photo credit: tarsandsaction, CC BY 2.0