The Paradox of Snow Storms in a Changing Climate
With our latest historic April snowfall behind us (relive it through exploring storm-total snowfall amounts here!), I thought it would be a good time to revisit the science of snowfall and climate change. The relationship between the two is a little more complex than it first appears, particularly in cold northern climates like Minnesota and Wisconsin.
HOW WINTER IS CHANGING
Science tells us that the earth has been warming for over a century; and, in the last half-century, the dominant cause of that warming is human activity. Science and common sense also tell us that, on a global scale, snow and ice cover will become less widespread and less likely.
These changes are already occurring, and are easy to see. This NASA time-series shows the extent of Arctic sea-ice coverage at the end of summer each year from 1979 to 2018. The visual tells a tale of progressively less ice, and numbers back that up; NASA measurements found that millions of square kilometers of sea ice have melted away in that time, at a rate of 12.8% loss per decade. But, what these numbers don’t show, is that there has also been a decrease in the quality and thickness of the sea ice.
That’s something I learned when I was invited to attend the Glen Gerberg Climate and Weather Conference in Breckenridge, CO this January. While there I had a chance to speak with Rick Thoman, an Alaska Climate Specialist with the University of Alaska and retired meteorologist for the National Weather Service. He explained how the decrease in coverage and quality of sea ice is already impacting society in Alaska.
“Certainly in western Alaska, where hunting and fishing on sea ice are millennia-old traditions… people that were doing this hunting and fishing in their youth in the 50s and 60s now see that their grandchildren simply do not have the same opportunities that they had.”
“What happens in the Arctic doesn’t stay in the Arctic,” Thoman reiterated. “Minnesotans can learn from Alaska’s example.”
A similar analysis of North American snow cover also shows a noticeable decline since the 1970s. Looking at data from Rutgers University Global Snow Lab and the National Center for Environmental Information, Climate Central found that the land area covered in snow has declined from an average of approximately 3.35 million square miles in 1973 to approximately 3.18 million square miles in 2016.
A recent report by the independent climate research and communications organization, Climate Central, shows serious consequences for cold-weather sports like ice fishing, skiing, and snowmobiling. In addition to contributing an estimated $11.3 billion of the national economy in 2015-16, winter sports are also a part of the societal fabric and civic pride in areas like ours.
LESS SNOW, BIGGER STORMS
Indeed, Winter (defined as the months of December, January, and February) is heating up in Minnesota. Average wintertime temperatures in the Twin Cities have risen 5.7°F since 1970, and the state leads the lower 48 states in the amount of winter warming.
Even in a warming world, snow will fall. However, the amount of snow and when it falls is changing as a result of a changing climate. According to a Climate Central analysis of publicly available weather data, the percentage of precipitation falling as snow in the Twin Cities dropped more than 15% from 1950 to 2015. And it’s not just the Twin Cities; in the Upper Midwest, 72% of long-term climate stations are receiving less snow now than they did in 1950. In fact, the Upper Midwest and Pacific Northwest are seeing the largest decreases in precipitation falling as snow over the past 66 years.
The actual amount of seasonal snowfall is also trending downward in the Twin Cities. Since 1970 the average seasonal snowfall has fallen slightly, from approximately 60 inches to just shy of 50 inches.
In many locations across the country, the reduction in overall snowfall is occurring during the transition seasons of late fall and early spring; the months when sudden warmups are more likely. However, here in Minnesota, it appears that those transition seasons… particularly during the Spring… are actually bringing larger storms.
Storm total snowfall from April 10-12, 2018 in the Twin Cities was 9.8”, the 5th largest April snowfall on record; two additional top-10 April snowfalls occurred in 2018. With reliable snowfall records back to 1891, this means that 30% of the largest April snowfalls on record have occurred in the last two years.
What’s more — this isn’t a fluke. A look the occurrence of two-day snowfall records nationwide show that more snowfall records have been set recently; a total of 43% of all snowfall records have occurred since 1980.
At first glance this seems counterintuitive, given warming global temperatures and less ice- and snow cover. Taking another look, though, reveals that warmer air can hold more moisture than cold air can; and, it’s the ability to hold additional moisture that is the culprit for “juicier” storms all year long.
And, while it’s true that transition seasons can bring unusual spikes in warmth, they can also bring unusual spikes in cold. If these cold outbreaks happen to meet up with a low-pressure system that’s been “juiced” with more moisture, that’s the recipe for a heavy snowfall.
So, while the earth continues to warm, a climate like that of Minnesota or Wisconsin can expect less snow each year, but heavier snow when it does fall. It’s a similar story in areas that are prone to lake-effect snow, which can only occur when the lake surface is unfrozen; a later ice-in and earlier ice-out due to warming temperatures would likely increase snowfall.
THE BOTTOM LINE
Storms like these are becoming more common in our warming world; the paradigm is already shifting. They can be a boon to winter sports lovers, but taxing to commuters and the municipalities that need to clean up after them (and find places to put extreme amounts of snow). The time to make a plan, and take action, is now.