In the realm of man-made global warming and climate science, any link to an extreme hurricane, like Sandy, is often described by scientists with a baseball metaphor. A slugger on steroids hits more home runs, but attributing any single home run solely to steroids is not a simple matter.
And asking whether steroids caused a specific home run -- or whether climate change is responsible for the massive hurricane that smashed into the Northeast -- may be the wrong question to ask. A better question might be: Are such storms becoming more likely than before, and will extreme weather become even more likely in coming years?
To that question, the scientific answer from experts who spoke to the Times Union was: Yes.
After surveying Sandy's damage this week, Gov. Andrew Cuomo weighed in, declaring that, "Anyone who says there is not a change in weather patterns is denying reality ... that's a whole political debate that I don't want to get into. I want to talk about the frequency of extreme weather situations, which is not political ... There's only so long you can say, 'this is once in a lifetime and it's not going to happen again.' "
The fundamental physics of climate change -- increasing emissions of greenhouse gases from fossil fuel combustion are gradually warming the atmosphere and the oceans -- are "indisputable," said Chris Thorncroft, chairman of the Department of Atmospheric and Environmental Sciences at the University at Albany.
A warmer atmosphere holds about 4 percent more water vapor than it did during the 1970s, and the number will continue to rise as the atmosphere warms. More water vapor means more clouds and "more rainfall, more heating, and the intensification of storms," Thorncroft said.
Climate models predict "more such extreme events, and I think we are starting to see it. People should not be talking about just one event. It is the increasing probability of such events," he said.
Superstorm Sandy was more than just a hurricane -- it was a hybrid storm that combined the forces of a tropical cyclone, or hurricane, and a winter storm, in which colder air from the north collides with warmer, moister air from the south.
A hurricane is fueled in part by the energy in warm sea water, and Sandy grew in Atlantic waters that are three degrees warmer than normal. Other factors also were in play -- Sandy was funneled up a kind of corridor formed by a blocking pressure front over Greenland and colder air that dropped from the Arctic into the United States. That pushed the storm to the east, and then inland over the coast.
And high tide when the storm hit was made a even a bit higher because of gravitational effect of the full moon, a factor that obviously had nothing to do with climate change.
Climate science is just beginning to understand such hybrid storms, and Sandy cannot be said to be definitive proof, by itself, of man-made climate change, said Kerry Emanuel, a climate scientist at the Massachusetts Institute of Technology.
"We don't know if this type of storm is going to increase in the future," he said. There is also uncertainty about whether the frequency of tropical hurricanes will increase in the future, as research is divided on that, he said.
But research does point to the larger, more destructive hurricanes becoming a larger share of the total number of hurricanes, he said. "Such storms will become a bigger piece of the pie," he said, explaining there may be fewer storms in the future, but a greater share of them could be extreme.
New York state climatologist Mark Wysocki said global warming caused by accumulating greenhouse gas emissions is "raising the background in which such storms like Sandy can develop ... climate change will provide more opportunities for extreme storms to develop."
Wysocki, who is based at Cornell University, said extreme weather around the world -- cold snaps in Europe, droughts in the U.S. Midwest, extreme rains in parts of Australia -- convince him that climate change is showing itself in emerging patterns of regional climate change.
"I am really concerned about the kind of climate that we are going into. It is changing," he said. "We should not be arguing too much about what it causing it. We need to talk about how we are going to live with this."
Decision on rebuilding "should be done with the knowledge that this is going to happen again. New York City has to take a very, very deep look at this," he said.
In July, a research paper published in the science journal Nature: Climate Change looked at the growing risk of storm surges in New York City as climate change continues to raise sea levels.
Global warming raises sea levels two ways -- by the melting of land-bound glaciers and ice, and by warming sea water, which causes water to expand. This century, sea level is up globally by about 8 inches.
Research author Michael Oppenheimer, a geosciences professor at Princeton University, said as sea levels continue to rise this century -- models estimate that increase could be between 7 and 23 inches, and much more if the Greenland ice sheet continues to melt -- storm surges along the coast will be able to reach further inland.
That could be ominous news for New York City and coastal residents. Oppenheimer's paper predicted that by the end of this century, the storm surge for a storm identical to Sandy -- which is now estimated at 14 feet above sea level -- could be another 5 to 6 feet higher, flooding that much more of the city and coastal communities.
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