Post-Sandy, the anxious ask: Is this climate change in action?

This story was originally published on Nov. 4, 2012:

Having transformed New Jersey's barrier islands into sand traps, humbled New York City, and darkened millions of households in a bustling population corridor, Sandy has set off new waves of anxiety about the state of the atmosphere.

Coming after yet another blistering summer, a renege "derecho" wind storm in June, record wildfires, and a hyperactive hurricane season, it is not surprising that Sandy has people asking: Is this the latest creation of an overheated atmosphere running amok?

"Any time there's a historic event, people want to attribute this to some reason," said Frank W. Marks, head of the National Oceanic and Atmospheric Administration's Hurricane Research Division.

"Yes, global warming is happening. Yes, sea-level rise is happening. I can see it here in Miami; it's coming up fast."

But "it's not like these events haven't happened before," Marks cautioned, mentioning destructive Hurricane Hazel, of October 1954, and, of course, the "perfect storm" of October 1991.

Still, while they aren't sure precisely how, climate experts are confident that subtle changes in Earth's temperatures are affecting day-to-day weather, and hence, the earth itself.

For instance, there is now free standing water in the Arctic. Scientists have no idea when that happened last. But they believe that the open ocean has been having an impact on the atmosphere above it. Specifically, they believe it may have led to more cold air masses making their way south.

That phenomenon could have contributed to the record snows of the winters of 2009-10 and 2010-11 in Philadelphia - 10 feet's worth - said Jeff Masters, meteorologist at the popular Weather Underground.

The stunning snow amounts also might have been tied to another effect of warming - a warmer atmosphere is capable of holding more water vapor.

But as surely as a megastorm such as Sandy will stir the global-warming debate, the climate community will be quick to caution that it is impossible to tease out background warming as a factor in any given storm.

Why?

One obvious reason is that the atmosphere remains on very low simmer. World temperatures have increased about 1.3 degrees since the late 19th century, according to the National Climate Data Center, although land and satellite-based measurements show the pace has picked up somewhat in recent decades.

Identifying the effects would be a whole lot easier if the warming were uniform, but it isn't. It has been far more robust in the Arctic, which is losing sun-repelling snow and ice, but the Southeastern United States actually has cooled slightly.

Climate interactions are immensely complex, what the scientific community calls a "nonlinear chaotic system."

Researchers have indicted global warming in increasing nighttime temperatures, a significant hazard during heat waves; an increase in extreme rain events in some parts of the country; and, most confidently, in rising sea levels.

Sea levels have been going up for 12,000 to 18,000 years, since the end of the last glacial epoch, the result of melting ice and thermal expansion - warm water takes up more room. But they have accelerated in the last 20 years, said Steven Gill, a researcher with the National Ocean Service, particularly off New Jersey.

They have risen about 0.18 inches annually there, compared with roughly 0.12 inches worldwide, he said. The higher water levels helped shut down New York, said Andrew Freeman, with the research group Climatecentral.org.

"Sea-level rise didn't cause this horrible event," he said, "but it did make the coastal flooding somewhat worse than it otherwise would have been."

But again, the fingerprints of global warming might be hard to identity in Sandy's aftermath. The New York flooding wasn't all about higher seas, said Marks; it had a lot to do with timing. Sandy probably would have been less disastrous had the center arrived at low tide, rather than high.

And warming isn't the only cause of rising seas along some of the world's coasts; land is sinking, part of natural geological processes. "The whole Eastern Seaboard is a subsiding coastal plain," Gill said.

While the precise human contribution to global warming may be debatable, human development had everything to do with Sandy's price tag, estimated at $30 billion by Roger Pielke Jr., a risk specialist at the University of Colorado. That would make it the 10th-most-expensive tropical storm on his historical list. Others have put the losses higher, at $50 billion.

"To call Sandy a harbinger of a 'new normal' would be wrong," he wrote last week. "This historic storm should remind us that planet Earth is a dangerous place, where extreme events are commonplace and disasters are to be expected."

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