By Claire

Climate change changes the odds of natural variability, making it much more likely that we will see warm extremes of climate.

A new paper published by the National Academy of Sciences, has attributed extreme temperatures experienced in the Northern Hemisphere over the last decade to climate change.

The research by a man often called the “godfather of global warming” says that the likelihood of such temperatures occurring from the 1950s through the 1980s was rarer than 1 in 300. Now, the odds are closer to 1 in 10, according to the study by NASA scientist James Hansen. He says that statistically what’s happening is not random or normal, but pure and simple climate change.

Unlike other studies that rely on models to differentiate between natural variability and climate change, this study uses real-world data and statistical analyses.

“Our analysis shows that it is no longer enough to say that global warming will increase the likelihood of extreme weather and to repeat the caveat that no individual weather event can be directly linked to climate change. To the contrary, our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change,” says lead author, James Hansen, director of the NASA Goddard Institute for Space Studies.

Changing probability of below average (blue), average (white) and above average (red) temperature events.

“The deadly European heat wave of 2003, the fiery Russian heat wave of 2010 and catastrophic droughts in Texas and Oklahoma last year can each be attributed to climate change. And once the data are gathered in a few weeks’ time, it’s likely that the same will be true for the extremely hot summer the United States is suffering through right now.”

“These weather events are not simply an example of what climate change could bring. They are caused by climate change. The odds that natural variability created these extremes are minuscule, vanishingly small. To count on those odds would be like quitting your job and playing the lottery every morning to pay the bills.”

“Twenty-four years ago, I introduced the concept of “climate dice” to help distinguish the long-term trend of climate change from the natural variability of day-to-day weather. Some summers are hot, some cool. Some winters brutal, some mild. That’s natural variability.”

“But as the climate warms, natural variability is altered, too. In a normal climate without global warming, two sides of the die would represent cooler-than-normal weather, two sides would be normal weather, and two sides would be warmer-than-normal weather. Rolling the die again and again, or season after season, you would get an equal variation of weather over time.”

“But loading the die with a warming climate changes the odds. You end up with only one side cooler than normal, one side average, and four sides warmer than normal. Even with climate change, you will occasionally see cooler-than-normal summers or a typically cold winter. Don’t let that fool you.”

“When we plotted the world’s changing temperatures on a bell curve, 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.”

“The change is so dramatic that one face of the die must now represent extreme weather to illustrate the greater frequency of extremely hot weather events.”

“Such events used to be exceedingly rare. Extremely hot temperatures covered about 0.1 percent to 0.2 percent of the globe in the base period of our study, from 1951 to 1980. In the last three decades, while the average temperature has slowly risen, the extremes have soared and now cover about 10 percent of the globe.”

(N.B. Quotes from James Hansen come from an opinion piece authored by him, published in the Washington Post)

The science in Hansen’s study is excellent “and reframes the question,” said Andrew Weaver, a climate scientist at the University of Victoria in British Columbia who was a member of the Nobel Prize-winning international panel of climate scientists that issued a series of reports on global warming.

“Rather than say, ‘Is this because of climate change?’ That’s the wrong question. What you can say is, ‘How likely is this to have occurred with the absence of global warming?’ It’s so extraordinarily unlikely that it has to be due to global warming,” Weaver said.