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Until recently, attributing the likelihood of specific events to climate change was extremely difficult. Climate change is a worldwide phenomenon, and the amount of computing power required to run models thousands of times to get accurate probabilities has been limited.

But as processing speeds have improved, data sets grown more robust, and demand for such information increased, it’s now become possible to estimate whether specific extreme weather phenomenon were caused by climate change, and whether they are now more or less likely to occur again. The findings from such studies have been published every year since 2011 in the Bulletin of the American Meteorological Society (BAMS).

Related: Ground zero of fight against rising seas: progress at a high cost

The most recent edition was released in late September. Perhaps the most surprising finding: three independent studies found that the California megadrought's link to human-caused climate change was inconclusive. One paper did find evidence that atmospheric pressure patterns increased due to human causes, but the influence on the California drought remains uncertain. Another group of researchers found that a major U.K. coldsnap in 2013 is less likely to occur again as a result of climate change.

Here is the scorecard from the latest series, which covers papers released in 2013:


The concept is relatively straightforward. Scientists recreate the atmosphere over the region they're looking at, then simulate current climate patterns thousands of times. They then take the same recreated region and run it through prior or alternative climate conditions thousands of times. Then they simply compare the difference in probabilities that event would have occurred.

Other findings of headline U.S. weather have phenomena have been more definitive. In the 2012 edition, a group looking at Superstorm Sandy concluded that thanks to rising sea levels, an event with similar inundation (which caused the most amount of damage, as opposed to wind), that would have previously have occurred just once-in-a-century or longer can now be expected to recur on the eastern seaboard every couple of decades.


For Tom Peterson, a meteorologist with NOAA, the goal of the series is to provide decision makers with useful information, even if it's only dealing in probabilities.

"If you're thinking about building a factory on the edge of a floodplain, and there's a really enormous flood, it'd be really helpful to know whether that's a really rare occurrence or so you can go ahead with the plan, or whether in the past it was an every-500-years event that from now once will be a once-every-50-years event," he told Fusion.

In the instance of the California drought, the damage of course has been very real. The takeaway from the studies is simply that we cannot yet say definitively whether this kind of event is likely to become more or less frequent.


Sebastian Sippel of the University of Oxford recently met with both emergency workers and investors from southeastern Europe about whether they'd find his study of a recent heatwave in the region useful. He said they embraced despite the fact that it only dealt in probabilities.

The series, and the science behind it, are still quite new. But readers can actually participate in some of these studies by logging onto weather @ home and turning over their idle computers to climate simulations.

Rob covers business, economics and the environment for Fusion. He previously worked at Business Insider. He grew up in Chicago.