Whether climate change was responsible for changing Hurricane Sandy's path that sent it on a left turn into mid-Atlantic states and inland is open to scientific debate.
Scientists remain uncertain whether melted Arctic ice caused the autumn high-pressure system in the North Atlantic, which sent Sandy westward, causing an estimated $50 billion in damage with the U.S. death toll topping 80.
But climate-change scientists generally agree that the sea levels that have risen by a foot over the past century, coupled with the high tide during a full moon, heightened the storm surge. There's less certainty, but general acknowledgement, that near-record surface temperatures of the Atlantic Ocean emboldened the hurricane with added energy and water vapor.
The Natural Resources Defense Council, a nonprofit environmental action group, says climate change heightened Sandy's power and could indicate a trend in which a storm of the century becomes the more common storm of the decade.
"The best overall characterization is that climate change puts extreme weather on steroids and the primary mechanisms for Sandy started with the fact a warmer atmosphere holds more moisture, so storms will tend to hold a higher amount of precipitation," said Daniel A. Lashof, director of NRDC's climate and clean air program.
Michael Mann, a Penn State University professor and director of the school's Earth Systems Science Center, said the one thing that's clear about Sandy is the likelihood that hurricanes increasingly will become more powerful as oceans get warmer.
"But one thing that doesn't get quite as much attention and yet is equally important is the potential for inland flooding with these storms," Mr. Mann said. "Few people are aware that much of the damage and expense from hurricanes and tropical storms isn't from the winds or coastal surge, but from inland flooding."
Massive flooding that occurred from Sandy is a direct result of climate change, and "that is why these events have become billion-dollar disasters," he said.
Simple physics explains how warmer ocean water temperatures increase the amount of water vapor in the atmosphere, he said. "Sandy crossed near-record ocean surface temperatures off the mid-Atlantic coast, taking on more water vapor and resulting in more flooding rain than would have occurred if ocean temperatures were cooler."
The more robust connections between Hurricane Sandy and climate change, he said, include the rise in sea level that contributed to the worst peak coastal surge of 13 feet at Battery Park in New York City and near-record sea surface temperatures off the East Coast.
He and other scientists say no one can blame global warming for any single hurricane.
"But we can see that climate change is playing a role in setting the context for these storms -- in particular the record levels of North Atlantic Ocean warmth that is available to feed these storm with energy and moisture."
Climate-change scientist Michael Oppenheimer, a doctor of geosciences at Princeton University, said the one-foot rise of sea level over the past century is attributable to global warming. "The storm surge was higher than it would have been without global warming."
As a result, he said, "the tide, wind speed and higher ocean level sent water farther inland."
He said it's still speculation whether climate change intensified Sandy. Even though the hurricane had a 1,000-mile diameter, it's unclear whether climate change affected the hurricane's structure, strength and trajectory. "The science is speculative and the question is whether warm ocean temperatures had an impact. I'm sure it had some effect but I'm not sure how much of an effect."
Other unresolved issues include climate change's impact on the jet stream and ocean currents. Some studies have linked such changes to storm intensity, but its impact on Sandy remains unclear.
"There is some speculation that the hurricane was affected by a blocking high [pressure system over the North Atlantic] created by the lack of Arctic ice," Mr. Oppenheimer said, noting that reductions in Arctic ice are a direct effect of global warming. The high actually did redirect Sandy's path to the west.
Sandy's current estimated damage of $50 billion would rank it second behind Katrina, which occurred in 2005 and caused more than $100 billion in damage. Sandy will raise awareness of climate change, which also has been linked to this year's drought in the Midwest and even the violent tornadoes of recent years.
First Published November 3, 2012 4:00 AM