Mon September 24, 2012
As Arctic Ice Melts, So Does The Snow, And Quickly
Originally published on Tue September 25, 2012 5:11 pm
Arctic sea ice is in sharp decline this year: Last week, scientists announced that it hit the lowest point ever measured, shattering the previous record.
But it turns out that's not the most dramatic change in the Arctic. A study by Canadian researchers finds that springtime snow is melting away even faster than Arctic ice. That also has profound implications for the Earth's climate.
Springtime snowmelt matters a lot: It determines when spring runoff comes out of the mountain to fill our rivers. And Chris Derksen at Environment Canada in Toronto says snow also reflects sunlight back into space, helping to keep the Earth from heating up too fast.
"When you remove the snow cover form the land surface, much as when you remove the sea ice from the ocean, you take away a highly reflective, bright surface, and you expose the bare land or tundra underneath, and that absorbs more solar energy," he says.
That darker land traps heat and warms the planet. Scientists have been keeping an eye on this trend for years.
But Derksen and colleague Ross Brown have produced a study, which has been accepted for publication in Geophysical Research Letters, that documents a dramatic increase in the speed of this snowmelt. It turns out that in May and June, snow across the far north is disappearing fast.
"It's decreasing at a more rapid rate than summer sea ice," Derksen says. "So the loss of snow cover across the Arctic is really as big an issue as the loss of sea ice."
Derksen expected to see a gradual decline, but he was taken aback when he reviewed satellite measurements for the past five years and saw the speed of this loss. Snowmelt decline is occurring at a rate of 18 percent per decade, versus 11 percent per decade for the much talked about Arctic sea ice.
"That was a bit shocking," he says.
It's also contrary to what scientists had predicted. There are more than a dozen research groups around the world who use computer models and simulations to forecast how quickly things are likely to change in our warming world.
Effects Of Melting Snow
"We're now losing spring Arctic snow cover at a rate faster than the models predict," Derksen says. And that "puts somewhat into question what the scenario will look like 10, 20 or 30 years from now."
Even today, the early spring snowmelt is of concern to biologists who study life in the far north. Syndonia Bret-Harte at the University of Alaska, Fairbanks, says this change affects the rivers that spawning fish rely on.
It also hastens melting of the permafrost, a layer of frozen soil that contains a lot of carbon. And when permafrost melts, it releases those greenhouse gases into the atmosphere. And then there's the matter of fires in the boreal forests.
"If things dry out faster in the spring, then you can get more fires, and that's another trend we see in recent years, is increased fire frequency and also the size of fires," says Bret-Harte.
And while the far north is feeling these effects most strongly, she says they affect us, too.
"Since the Arctic acts as the air conditioner ... for the rest of the Northern Hemisphere, heating up in the Arctic is also probably going to cause feedbacks to heating up in the more southern climate."
Researchers say global warming is no doubt contributing to this early melting of spring snow. And Philip Mote at the Oregon Climate Change Research Institute says there may be a relationship between the rapid loss of sea ice and the early snowmelt.
Early spring snowmelt "may help set up the Arctic to absorb heat and melt the sea ice faster, so that by late summer, this time of year, we can see very low levels," Mote says.
But there's one big difference between snowmelt and the sea ice melt. Because the sea ice is getting thinner and less resilient every year, it seems inevitable that the melting trend will continue. But Mote says the long-term buildup of greenhouse gases may not be the whole story for spring snowmelt.
"The atmosphere and the ocean do different things year to year, and that can also affect the snow cover in ways that are independent of greenhouse gases," he says.
So Mote is not so sure this dramatic trend of recent years will keep on its downward spiral. That said, the long-term trend is clear: less snow, less ice and more warming.