Extreme winter weather often prompts a fresh wave of public skepticism from those who doubt the existence or severity of human-caused climate change. When the Northeast USA received 2 feet of snow earlier this month, President Trump tweeted, “Wouldn’t be bad to have a little of that good old fashioned Global Warming right now!”
As experts point out, short-term variations in the weather—even when they result in extreme snowfall or record-breaking cold—don’t negate the long-term trend of global warming. Decades of data unambiguously demonstrate that average temperatures all over the world are on the rise.
But when it comes to winter weather, and specifically snow, teasing out the effects of climate change is a special challenge. It seems as though snow—arguably the most iconic feature of a cold climate—should be one of the most obvious indicators of global warming. But scientists are finding that it’s not that simple.
Climate change has conflicting influences on snow. In many places, rising temperatures may increase the chances that snow will turn to rain before it hits the earth or that it will melt faster once it’s on the ground. On the other hand, warmer air is capable of holding more moisture and producing more precipitation. That means in some very cold climates, where there’s still plenty of room for temperatures to stay below freezing, warming could actually cause an increase in snow.
Scientists broadly agree that snow will change in most places as the climate continues to warm, said David Robinson, New Jersey’s state climatologist and head of the Rutgers University Global Snow Lab. But exactly how and why, from one location to the next, may be among the most challenging questions about weather and climate change.
A paper published last March found that about a third of all monitoring sites in the western United States are showing significant snowpack declines and that the total amount of water stored in the average April snowpack has declined by 21 percent since 1915. A 2011 paper said the recent declines are likely the most dramatic the region has seen for a thousand years.
A 2016 analysis of satellite records also pointed to a broad pattern of decreasing snow cover across the Northern Hemisphere, particularly in the spring, with the strongest effects seen in western North America and Eurasia.
But the researchers note that the coldest parts of North America—namely, Canada and parts of the northern United States—might be expected to actually see an increase in the amount of snow.
Gerard van der Schrier, a scientist with the Royal Netherlands Meteorological Institute, says that two seemingly conflicting snow trends can be true at the same time. Some of van der Schrier’s research published last year found widespread declines in snow depth across much of Europe. But in the very coldest places, he pointed out, the opposite appears to be true.
[Scientific American, as reprinted from Climatewire]