Climate Matters•January 23, 2019

Warming Winters: On Thin Ice

Warming Winters: On Thin Ice
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KEY POINTS

  • Despite the recent cold snap, warming is transforming America’s winters

  • Snowfall patterns are changing, and winters have warmed up in cities across the U.S.

  • These trends will have profound effects for the country’s valuable winter recreation sector

  • A new Climate Central report spells out these patterns and their consequences

COLD, HARD CASH

Winter recreation contributes billions of dollars to the U.S. economy every year. From ice-fishing to downhill skiing, cold-weather sports encourage Americans to spend money on lodging, food, and travel — spending that reaches far beyond lift passes and equipment purchases. In the 2015-16 season, the skiing and snowmobiling sectors alone supported more than 191,000 jobs and contributed roughly $11.3 billion to the national economy. And outdoor winter sports have immeasurable cultural value.

All outdoor winter sports need low temperatures or ample snowfall — and global warming has already shaped both. A new report from Climate Central explores these changes in depth.

DEFROSTED

First, take temperature.

Climate Central looked at winter temperature data from 244 weather stations, dating back to the 1970s, and found that the American places where winters have warmed the most are mostly cold ones. Winters in Burlington, Vermont, for instance, have warmed 7°F since the 1970s. Winters in Minneapolis have warmed by about 5.7°F. And in both Milwaukee, Wisconsin, and Concord, New Hampshire, winters have heated up by 5.6°F. In total, 17 weather stations saw average winter temperatures rise by 5°F or more, and 191, or 78 percent, saw increases of 2°F or above. (Cold snaps like the one that has recently affected much of the country are becoming less frequent.)

One way to assess the impact of these trends for winter recreation is to consider where average winter temperatures have risen from below to above freezing — the point at which the snow and ice on which winter sports depend begins to melt. In the 1970s, 107 of the the 244 weather stations assessed experienced average winter temperatures below freezing. Between 2009 and 2018, just 95 did — a decline of roughly 11 percent. Among the places where average temperatures climbed above freezing were Salt Lake City, Utah — the urban hub of a major winter-sports region — and Boston, Massachusetts, where temperatures have risen by 2.3°F since the 1970s. According to work by researchers at Wilfrid Laurier University, the number of annual days ideal for outdoor ice skating has roughly halved in Boston since the 1950s.

"The science demonstrates that we have fewer days with natural snow cover, shorter windows to make snow, and increased likelihood of mid-winter thaw and rain,” added Dr. Elizabeth Burakowski, a Research Assistant Professor at the University of New Hampshire’s Institute for the Study of Earth, Oceans, and Space. “Warmer, low snow winters impact skier visitation at a cost to mountain communities. Billions of dollars are on the line, and reducing greenhouse gas emissions would limit the losses."

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By midcentury, every state in the contiguous United States is projected to see fewer days with low temperatures below freezing each year. All outdoor winter sports depend on those temperatures. The extent of the change depends on the amount of warming pollution that humans put into the atmosphere. Consider Colorado, where winter rec supports some 43,000 jobs. Compared to the 1981-2010 average, unchecked emissions would slash the number of below-freezing days in the average year by more than two weeks between 2020 and 2039, according to the Climate Impact Lab, a research group. In the average year in the 2040-2059 period, the state would lose 34 below-freezing days relative to recent conditions. By midcentury, in other words, failure to curb emissions could rob America’s biggest winter-sports state of more than a month of below-freezing days. Moderate emissions cuts, roughly in line with the 2015 Paris agreement, would limit the number of lost below-freezing days to 26 — saving eight crucial days of snow-friendly temperatures.

"Warmer temperatures and less snow means a shorter season for snowboarders and skiers," said Jamie Anderson, a professional snowboarder and two-time Olympic gold medalist.

LET IT SNOW?

Next, consider snowfall.

The big-picture trend: since the 1970s, 57 of 107 U.S. weather stations assessed by Climate Central have seen average annual snowfall trend downward by at least an inch. In total, 17 weather stations saw declines of at least a foot of snow. The results showed regional differences, separating the stations that saw diminished snowfall, many in the Western United States, from those that recorded significant increases, as in the Great Lakes region.

The biggest losers were Flagstaff, Arizona; Salt Lake City, Utah; and Casper, Wyoming, all of which are historically snowy cities with connections to winter sports. In those cities, the annual snowfall trendline dropped by 48, 31, and 29 inches, respectively. Warming has cut the portion of winter precipitation that falls as snow —  and that trend is especially pronounced in the Western United States. Some Western regions are also affected by what are increasingly becoming chronic drought conditions, which decrease the amount of precipitation that falls overall. Arizona, for instance, has been in a long-term drought for more than two decades; the fall and winter of 2017-18 were Flagstaff’s sixth-driest on record.

The three weather stations that saw the biggest upward trends in annual snowfall all lie near the Great Lakes: Marquette, Michigan; Erie, Pennsylvania; and Youngstown, Ohio. At those locations, trends translate into increases in annual snowfall of 68, 33, and 30 inches, respectively. As winters warm, on average, there is less ice, and hence more open water, on the Great Lakes. Warmer water temperatures, meanwhile, support more evaporation. The interplay of these effects produces an increase in lake effect snowfall in these nearby cities. This trend will only hold as long as winter air temperatures in the region are cold enough for snow in the first place.

A number of the other stations with snowfall gains of ten inches or more were big Northeastern population centers, such as Philadelphia, Boston, New York City, and Newark, New Jersey. That is consistent with a broader warming-driven trend, in which the Northeast has seen a major increase in the frequency of heavy precipitation events.

These trends and others have been on display in this year’s winter. “Both global warming and a weak El Niño are influencing weather around the world,” said Dr. Kevin Trenberth, a distinguished senior scientist at the National Center for Atmospheric Research. “Warmer oceans bolster the moisture available, and the rains and snows can be heavier as a result.” In California, major storms have dumped several feet of snow.

*For more information, explore ON THIN ICE: How Climate Change is Shaping Winter Recreation, Climate Central’s new report on winter warming, snowfall, and recreation.

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