Climate change responsible for super-charging winter storms, scientists say

Winters may be getting shorter, but watch out when it does snow: climate change is super-charging storms like the blizzard engulfing the American north-east, scientists said on Monday.

The heavier storms of recent years – snowfalls that shut down cities and brought heavy flooding to coastal areas of New England – carried the imprints of climate change, as researchers get better at detecting the fingerprints of global warming, even from snow.

It was too soon to pin the current storm to climate change, but a trend line was emerging, the scientists said.

“The snow season is getting shorter,” said Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research. “But the interesting thing is you can end up with heavier snows in part because of climate change.”

In general, climate change produces more extreme precipitation in North America – and if it’s cold enough, that produces snow.

“There is a little bit more oomph to these storms when they do develop, the so-called nor’easters in particular,” said

Nor’easters pack their punch from the contrast between cold land temperatures and the warmer Gulf stream and surrounding waters. Five of New York’s biggest snow storms have occurred since 2000, and 2014 was the hottest year in 130 years of temperatures records.

Ocean surface temperatures off the US Atlantic coast were unusually warm last year – about 2F above normal over huge expanses of the Atlantic off the east coast.

As result, there was about 10% more water vapour in the atmosphere, Trenberth said. Approximately half of that extra moisture was due to climate change, he said.

Every a 1F difference in temperature produces about 4% more moisture.

“You can easily get as much as 20% more snow out of a storm than you would otherwise, as long as it is cold enough so that all of that moisture gets converted into snow. And that is usually the case in the wintertime,” Trenberth said.

Researchers identified a similar interaction inland, known as the lake effect – when cold air meets water that has still not frozen over – well before last November’s white-out in Buffalo.

The current storm’s projected accumulations – above 2ft in the New York area and around 3ft in Boston – could rank among the biggest in the 130 years since records began.

The so-called Juno blizzard is also bound to create impacts not traditionally associated with blizzards – storm surges and coastal flooding, especially in the Cape Cod area. Sea level rise off the east coast is already expected to be about 8in – or more – by the end of the century.

“Flooding is going to be a major issue for the Cape and New England,” said Bernadette Woods Placky, a meteorologist at Climate Central. “The way this storm is just bombing out of there – just the intensity it’s creating off the coast – it is going to add even more water and pull it on to shore,” she said.

“It is everything interconnecting and exploding all at once.”

Scientists hesitate to link individual storms to climate change and said repeatedly that this week’s storm was not caused by climate change.

But scientists, zeroing in on the causes of individual storms, now believe about 35% of the rain that came down with hurricane Sandy was produced by climate change. On Monday, New York governor Andrew Cuomo reiterated his observations from that storm, citing “a pattern of extreme weather”.

Researchers are also beginning to detect the hand of climate change on winter storms.

The so-called Snowmageddon of February 2010 also saw unusually high surface temperatures in the Atlantic, with temperatures up to 3F above normal that led to exceptional amounts of moisture being fed into the circulation of the storm and resulted in exceptional snow amounts in the Washington DC area.

The landmark United Nations IPCC report on climate change warned that nor’easters like this week’s storm could grow stronger with climate change, because they are driven by the contrast between Arctic air and warming sea surface temperatures.

“There is no doubt that a component of that anomalous warmth is due to human-caused climate change. Those warm ocean temperatures also mean that there is more moisture in the air for this storm to feed on and to produce huge snowfalls inland,” Michael Mann, a climate scientist at the University of Pennsylvania, said in a statement.

“Climate change is making these sorts of storms more common, much as it is making Sandy-like superstorms and unusually intense hurricanes more common.”

Those storms were not created by climate change, Mann said. But, he added: “They were likely made worse by climate change.”