A car sits in the ditch as a winter snow storm bears down on Buffalo, N.Y., on Friday. (AP)

Climate change may or may not have helped generate the nor’easter lashing the East Coast this weekend. Such storms happen with some regularity, after all. But the amount of snow the storm called “Nemo” ultimately dumps, and the extent of flood damage it leaves in its wake, may well have ties to global warming, climate scientists suggested.

Michael Mann, a climatologist who directs the Earth System Science Center at Pennsylvania State University, compared a major storm like Nemo — or Hurricane Irene or Superstorm Sandy, for that matter — to a basketball slam-dunk with a lower net.

“If you take the basketball court and raise it a foot, you’re going to see more slam-dunks,” Mann said. “Not every dunk is due to raising the floor, but you’ll start seeing them happen more often then they ought to.”

The two key ingredients in a big snow: just cold-enough temperatures and a lot of moisture. Combine the chilled air converging on the East with the massive moisture coming from the Gulf of Mexico region and you’ve got the “perfect setup for a big storm,” Kevin Trenberth, of the Climate Analysis Section at the National Center for Atmospheric Research in Colorado, told The Huffington Post in an email.

As Trenberth explained, the ideal temperature for a blizzard is just below freezing — just cold enough to crystalize water into snow. Below that, the atmosphere’s ability to hold moisture to create those snowflakes drops by 4 percent for every one degree Fahrenheit fall in temperature.

“In the past, temperatures at this time of year would have been a lot below freezing,” Trenberth said. In other words, it’s been too cold to snow heavily. But that may become less of an obstacle for snow in the Northeast.

In addition to warming the air, climate change is adding moisture to it.

Sea surface temperatures are about two degrees Fahrenheit warmer than they were before 1980, raising the potential for a big snow by about 10 percent, according to Trenberth. And any individual storm, including this nor’easter, will pick up more moisture as it spins across a warmer ocean. What’s more, as Mann explained, a warm ocean clashes with cold air masses from the Arctic. A bigger contrast in temperatures may mean a bigger storm, he said.

Michael Oppenheimer, a climate change expert at Princeton University, said global warming is increasing extreme storms. “Storms like this tend to be heavier than they used to be,” he told HuffPost. “That’s a fact.”

As HuffPost reported on Friday, National Oceanic and Atmospheric Administration records show that the Northeast saw a 74 percent increase in precipitation during the heaviest rain and snow events from 1958 to 2011.
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Still, connecting any specific weather event to global warming remains inexact. A new area of study called “event attribution science” is mining data in an attempt to make more definitive links, or at least better gauge the odds of an extreme event in the context of climate change that results partly from human activities, including burning fossil fuels. But the field is young.

And, truth is, nor’easters happen.

In fact, Jeff Masters, a climatologist and founder of Weather Underground, noted that the number of intense nor’easters hasn’t increased over the last three or four decades. A warmer climate, he explained, can decrease the length of the snowy season, and therefore the time window for nor’easters.

Further, nor’easters are defined not only by heavy snowfall, but by high winds. There’s less evidence for links between winter winds and climate change. Warm weather storms, such as Hurricane Irene and Superstorm Sandy, are another story. “Since hurricanes are heat engines, they drive power from ocean waters,” said Masters.

Another climate-linked ingredient could propel this weekend’s storm into the history books: rising sea levels.

“A three-foot storm surge, on top of a higher sea level, will do more damage,” Masters said, noting that sea levels in Boston, expected to bear the brunt of the nor’easter with an historic storm surge, have risen a foot in the last 90 years.

Penn State’s Mann also likes to use baseball metaphors when describing climate’s influence on major storms — “home runs,” he calls them. “What we’re seeing now with climate change is weather on steroids.”

Matt Rourke / AP file

People play in water from an open fire hydrant during the afternoon heat on July 18, 2012, in Philadelphia. July was the hottest month ever on record in the contiguous U.S.
By Elizabeth Chuck, NBC News
If you found yourself bundling up in scarves, hats, and long underwear less than usual last year, you weren’t alone: 2012 was the warmest year on record in the contiguous United States, according to scientists with The National Oceanic and Atmospheric Administration.

The average temperature for 2012 was 55.3 degrees Farenheit, 3.2 degrees above normal and a full degree higher than the previous warmest year recorded — 1998 — NOAA said in its report Tuesday. All 48 states in the contiguous U.S. had above-average annual temperatures last year, including 19 that broke annual records, from Connecticut through Utah.

It was also a historic year for “extreme” weather, scientists with the federal agency said. With 11 disasters that surpassed $1 billion in losses, including Superstorm Sandy, Hurricane Isaac, and tornadoes across the Great Plains, Texas, and the Southeast and Ohio Valley, NOAA said 2012 was second only to 1998 in the agency’s “extreme” weather index.

Advertise | AdChoicesA long-term warming trend for the U.S., combined with drought and a northerly jet stream, led to the record heat, explained one of NOAA’s scientists.

“During the winter season, the jet stream tended to stay further north of the U.S.-Canadian border, so that limited colder outbreaks in the country. It also limited precipitation. So that led to a warm and dry winter season, and that persisted through the spring,” Jake Crouch, a climate scientist from the NOAA National Climatic Data Center, said.

“That warm and dry spring and winter laid the groundwork for the drought we had this summer… . When we have drought, it tends to drive daytime temperatures upward.”

The unprecedented warm weather wasn’t contained to the United States.

A corresponding rise in global temperatures prompted the World Meteorological Organization to call the rate at which the Arctic sea ice was melting “alarming” in its Nov. 28, 2012, report.

“The extent of Arctic sea ice reached a new record low. The alarming rate of its melt this year highlighted the far-reaching changes taking place on Earth’s oceans and biosphere. Climate change is taking place before our eyes and will continue to do so as a result of the concentrations of greenhouse gases in the atmosphere, which have risen constantly and again reached new records,” World Meteorological Organization Secretary-General Michel Jarraud said.

Each year since 2001 has been among the warmest on record worldwide, with 2012 likely to “be no exception despite the cooling influence of La Niña early in the year,” the report added.

‘Horrible’ sea level rise of more than 3 feet plausible by 2100, experts say

Watch NBC’s special coverage of the 2012 drought

NOAA expects to have global data for 2012 sometime in the coming weeks, but Crouch said scientists already know with certainty “it’s going to be in the top ten” warmest years ever.

Adding to the extremes: 2012 was the driest year on record for the U.S., with 26.57 inches of average precipitation — 2.57 inches below average. Those dry conditions created an ideal environment for wildfires in the West, which charred 9.2 million acres — the third highest amount ever recorded, NOAA said Tuesday.

Other notable climate activity from 2012:

•Snowpack totals across the Central and Southern Rockies were less than half normal.
•July was the hottest month ever on record in the contiguous U.S.
•Tornado activity was concentrated toward the beginning of the season, with large outbreaks in March and April in the Ohio Valley and Central Plains, but the final 2012 tornado count will likely be less than 1,000 — the least since 2002. “The factors behind that are kind of related to what was going on with the drought. We didn’t have these large storm systems moving through the country, so that limited precipitation, and that also limited severe weather outbreaks,” Crouch said. What made this year so high on the extreme weather index were cyclones, hurricanes, and the heat, he said.
•Alaska was cooler and slightly wetter than average, and had a record-cold January. “Their January temperatures were 14 degrees below average. Many locations in Alaska had temperatures 30 degrees below zero,” Crouch said, adding that Anchorage, Alaska, set a new snow record.
•Hawaii experienced growing drought conditions, with 47.4 percent of the state experiencing moderate-to-exceptional drought at the beginning of 2012 and 63.3 percent at the end of the year. Alaska and Hawaii were not included in the bulk of NOAA’s 2012 report because of terrain issues, and because scientists don’t have records dating back as far as states in the contiguous U.S.
Advertise | AdChoicesWhile NOAA made no meteorological forecasts for 2013, Crouch said the drought was going to continue to be an issue.

“The drought got a lot of attention this summer when it was having impacts on agriculture. More than 60 percent of the country is still in drought,” he said. “And if things don’t change, the drought is going to continue to be a big story in 2013.”