Last week’s Northeast snowstorm and extended power outages have focused renewed attention on extreme weather. But was this event related to climate change? Most press coverage says no, and as a result the press are well on their way to getting the story wrong.
Scientists are increasingly recognizing that climate change plays a central role in the extreme weather events that are slamming people and communities around the world. This week press coverage began of an IPCC report on extreme weather due out in two weeks, which will identify a better than 90 percent chance that climate change will bring more severe weather in our future.
And also this week, Kevin Trenberth, a scientist with the National Center for Atmospheric Research in Boulder, CO published an article urging scientists to change their fundamental research format on extreme weather from an assumption that climate change isn’t responsible to an assumption that it is responsible, to reflect the reality that climate change is occurring and influencing every storm.
“Humans are changing our climate. There is no doubt whatsoever…So why does the science community continue to do attribution studies and assume that humans are having no influence as a null hypothesis?” wrote Trenberth. Now some of you probably are ready to stop reading with a phrase like null hypothesis , but stick with me.
Scientists work by identifying a default expectation (which they call a null hypothesis so as to confuse eager graduate students), and then trying to disprove it. So what Trenberth is proposing is that the scientifically correct default expectation is that climate change influences everything, last weekend’s storm included. “These changes are universal so that all storms are now operating in an environment that has changed, and even a ‘normal’ storm must have heavier precipitation than it would have had 40 years ago.”
By continuing to assume that climate hasn’t changed and then trying to test for whether it has, Trenberth argues, scientists are making a series of errors that “grossly underestimate the role of humans in climate events of note in recent times.”
In the case of the Northeast snowstorm, this quote from Seth Borenstein’s coverage of the IPCC report has been spread far and wide (I even found it quoted in a Taiwanese newspaper): “The snow-bearing Nor’easter cannot be blamed on climate change and probably isn’t the type of storm that will increase with global warming, four meteorologists and climate scientists said.”
But there are two ways that climate change amplified the effects of the Northeast storm. First, we’ve had an extremely warm fall. In the Berkshire Hills of western Massachusetts, where I live, we didn’t have a killing frost until October 27th. That’s the day I harvested the last of the okra , peppers, and winter squash from the garden—fully a month after a normal fall’s first frost date. That late fall meant that trees still had their leaves, and hence that the snow broke far more branches and therefore damaged power lines much more than it would have in a normal fall. For the people still waiting for power nearly a week later—that’s a climate change related extreme.
And the volume of water in the storm also was likely influenced by climate change. The storm brought the heaviest October snow in New England in more than 200 years—since the “snow hurricane” of 1804. A once-in 200 year event is probably extreme by most people’s definition. The link to climate change, as Trenberth points out is that global warming has increased the amount of water in the atmosphere by about 4%, “thereby increasing the intensity of precipitation (rain and snow).”
Frank Lowenstein is Adaptation Strategy Lead for The Nature Conservancy’s Global Climate Change Team.
Photo by: Frank Lowenstein/The Nature Conservancy (Apple tree braving the Halloween Nor’easter)
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