The answer to the oft-asked question of whether [a particular extreme weather] event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be….
— Kevin Trenberth, head of the Climate Analysis Section at the USA National Center for Atmospheric Research
As I write this on a pleasant Tuesday morning in Oregon, hurricane Sandy has just passed through the North Atlantic coastal states and is ravaging inland areas from New York State to West Virginia on its way to Ontario, Canada. The National Weather Service has issued flood warnings for Chicago where 50 m.p.h. winds are expected to bring waves as high as 23 feet to Lake Michigan’s shoreline. Moisture carried inland by the storm is meeting advancing cold fronts, and massive snowfalls are expected as far south as North Carolina.
Inundated with sea- and rainwater, coastal cities from Delaware to Rhode Island have been brought to a standstill, and now face an enormous cleanup job. Sandy is the largest hurricane ever to hit the U.S. North Atlantic coast. The cost of repairing the infrastructure and property damage will likely be three times higher than the $15.6 billion spent cleaning up after the monster storm Irene struck the region in 2011.
And of course the human toll of the storm — the deaths, disappearances and injuries; the loss of homes, communities and livelihoods; the traumatization of children — is incalculable.
Significantly, a few days before Sandy struck the U.S. another storm — a storm of controversy about whether the hurricane’s unusual characteristics could be attributed to global warming — erupted in the blogosphere. That’s because Sandy’s enormous size and power, and the fact that an extremely anomalous high pressure system over Greenland pushed it westward toward landfall, depended on a confluence of underlying climatic conditions and previously rare weather events that could become more common in our rapidly warming world.
When this combination of factors was described by meteorological agencies to explain why Sandy was such a dangerous storm (staffers at NOAA called it a “Frankenstorm,” because it was a rare “hybrid” of tropical and North Atlantic cyclones arriving at Halloween), supporters and opponents of the idea of human-induced climate change jumped to make their cases, and a heated, sometimes vehement brouhaha ensued.
My take? Along with 98 percent of the world’s climatologists, I consider the fact that humans are heating the planet by emitting greenhouse gases into the atmosphere to be settled science. But exactly what effects can we attribute to this global warming? Does it “cause” outsized hurricanes? Or, as some “global warming skeptics” maintain, are they merely natural phenomena that have and always will occur on this planet, regardless of human activity?
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Surprisingly, the answer is — quick, grab your cognitive-dissonance shield! — “all of the above.”
Of course there have always been hurricanes, some quite powerful and some influenced by distant, unusual weather patterns. Global warming doesn’t necessarily create the conditions under which hurricanes (or other extreme weather events) arise. But it does exacerbate those conditions — and increase the likelihood that an “average-sized” future hurricane will be larger and more powerful than “average-sized” hurricanes of the past.
Hurricanes generally become stronger as they pass over warm water and then they weaken over cooler water and land. Globally, September 2012 had the second-highest ocean surface temperatures on record, and the North Atlantic, over which Sandy traveled, is currently about 5ºF warmer than average, which helped the hurricane picked up strength and speed at its core as is lumbered northward.
Also, global warming has now laden the atmosphere with 5 percent or more moisture than it had a few decades ago. A September 2012 National Geographic magazine article states, “In theory extra water vapor in the atmosphere should pump heat into big storms such as hurricanes and typhoons, adding buoyancy that causes them to grow in size and power…But the jury’s still out on whether any increase has occurred yet.”
Sandy generated storm-force winds across its entire 1100 mile girth as it hit the coast. Is it the first juror to cast a vote in our new era of destabilizing climate — the first superstorm in a century of superstorms?
More important, do we want to find out? No one knows exactly what the future will bring, but many climatologists have predicted an age of superstorms, rising tides and unending droughts. Perhaps Sandy just told us that that future has arrived — and we’d better make some changes at our ecological house.