A new storm threatens with blizzards, floods and winds
Another major weather system will pound parts of the central and eastern United States through the weekend, including blizzard conditions, strong winds and severe weather.
Will climate change mean fewer big snowstorms like the blizzards on both coasts and across the country this week?
You might be surprised. Researchers studying how a warming climate is changing snowfall and snowfall are drawing new conclusions about the future of snow, and it's a mixed bag. Some researchers find total snowfall is declining in many areas, leaving less snow piled up on mountain ranges in the spring, while others say warmer winters won't prevent some of the more intense blizzards — at least not yet.
A new study by two Dartmouth College researchers looked at the decline of spring snow in large northern hemisphere river basins. They concluded that the losses may already be greater than anyone has realized, in part because they are so difficult to measure. Their study, published Wednesday in the journal Nature, linked human-caused warming to declining snowpack in at least 31 river basins in the hemisphere since 1981.
The researchers say their findings present “the most compelling evidence yet” that human greenhouse gas emissions have affected snow and critical water resources in the southwestern and northeastern United States, as well as central and eastern Europe.
The study is “a conservative estimate of the impact of global warming on snow to date,” said senior author Justin Mankin, an associate professor of geography at the college. “If anything, I would expect the impacts to be much greater for many places. We systematically underestimate the impact of global warming, particularly its impact on snow.”
Meanwhile, a study on Snowfalls in the Eastern US and Canada published in June found that snowfall is changing, but not uniformly. Snowfall totals have decreased in some areas and are expected to decrease further, but have increased in other areas, many of them concentrated along the coasts.
More extreme daily snowfalls, however — like those seen last weekend in New England — are likely to continue, even in a warming climate, at least as long as it's cold enough for snow to fall, the study found.
Warmer air produces more moisture, so if the air is warmer — but still cold enough to make snow — more snow is available to fall in extremes, scientists told USA TODAY. This study also found that a greater proportion of annual snowfall along the US-Canada border is likely in fewer but larger events.
Study finds less spring snow sitting on ground in US
Snowfall and snowmelt provide vital water resources to communities, farms and ecosystems in river basins around the world.
Mankin and Alexander Gottlieb, a doctoral candidate at Dartmouth, were drawn to their study by the challenges of measuring snow water content and because of the serious implications of water loss.
Although climate scientists have improved ways of measuring sea level, precipitation, drought, and other weather and climate patterns, accurate measurements of snow and its water content have remained elusive. Gottlieb said the use of satellites to measure snow cover has improved, but it's still “difficult” to get the true volume of snow mass on the ground.
Ultimately, the researchers combined historical observations of snow mass with snow records and climate models to predict how human-induced climate change might affect snow.
Jouni Pulliaine, a research professor at the Finnish Meteorological Institute whose analysis of the study's methods was also published in Nature on Wednesday, said the pair had created “a very promising approach”.
Researchers have documented snow loss in the spring, but no widespread losses have yet been reported, Mankin said. That's likely because most of the snow in the Northern Hemisphere accumulates in places that are still so cold that several degrees of global warming haven't been enough to melt it, he said. However, the snowpack becomes more sensitive to warming when winter temperatures reach above minus 8 degrees Celsius, he said.
That means bigger reductions are likely in the future, he said. “Once you get into that regime of accelerating snow loss, the trend is just going to be downward.”
This could cause cascading problems for downstream communities and infrastructure built around snowmelt runoff expectations.
Severe blizzards won't disappear as soon as the Earth warms
Although warming is projected to reduce annual snowfall across much of eastern North America, co-authors of the June study said significant snowstorms will still occur.
“We know that as the planet warms, we expect more precipitation in general across the northeastern US and southeastern Canada,” said lead author Christopher McCray. “But in the winter, because it's getting warmer, we expect less and less snowfall overall.”
But extremes change differently than averages, said McCray, a scientist for Orono, a climate services group that works with the Quebec government.
The top 5% of snowfall events, the biggest and most intense, like the howling Norwegians blowing into Boston with lots of snow, will continue. Even with 4 degrees of warming, McCray said, “you still see blizzards that are like the most intense blizzards.”
“Overall, we'll have less snowfall, but we'll lose more of the smaller snowfall events and keep many of the larger snowfall events,” McCray said. “In some places, they may appear less often, but they're not going to disappear.”
In northern New England, upstate New York and southern Canada, that means more days where a large percentage of snow falls on one day and fewer days of snowfall overall, he said.
So far, parts of the Northeast appear to be bucking the trend toward declining snowfall in a warming world, said Brian Brettschneider, study co-author and Alaska climate scientist. “But you're on borrowed time.”
“Theoretically, if all the ingredients come together for a blizzard, the warmer air can hold more moisture and you can dump more snow,” he said. “As Boston continues to get warmer and warmer, it's just going to be less cold. air to create snow'.
But other regional patterns could be at play, he said. For example, there is uncertainty about whether climate change may favor storms in the Northeast that produce more snow.
In the Great Lakes region, some areas are seeing less snow while others are seeing more snow, said Bryan Mroczka, a meteorologist at NOAA's Great Lakes Environmental Research Laboratory.
Warmer temperatures and delayed lake ice growth mean extended seasons with the potential for snow near the coast, Mroczka said. However, areas further inland see less snow during warmer winters.
In Anchorage, Alaska, snowfall between December and February has increased 20 percent over the past 50 years, Brettschneider said. But the snow season has been compressed, with less snow in October, November, March and April.