People ski on 'stocked snow', made by using snow that fell earlier in the winter months, at La Bresse-Honeck ski resort in France last month.SEBASTIEN BOZON/Getty Images
Of all the effects that climate change is having on the planet, one of the hardest to discern is a change in snow accumulation. So far this year, residents of some Canadian cities have found themselves shovelling less than in winters past, but snowfall is such a variable element of the weather that broader trends are not easy to pin down.
Now, a new study has linked an overall reduction in snowpack – the volume of snow that is present on the landscape – to human-caused global warming, and points to the likelihood that more dramatic changes lie ahead. The results forecast implications for ecosystems and watersheds that are supplied by melting snow every spring, and a change in how people who live in northern countries such as Canada come to experience winter.
Significantly, the study shows that even a modest further increase in warming could translate into a major reduction in snowpack. In some places where a thick white blanket was once the norm during the coldest months, abundant snow may eventually persist only in the memories of those who have lived long enough to experience it.
“I was surprised at the magnitude” of the projected change, said Justin Mankin, a climate scientist at Dartmouth College in Hanover, N.H., and senior author on the study, published Wednesday in the journal Nature. “I think it really shifts the extent to which we can use the past as a predictor for the future.”
For their study, Dr. Mankin and doctoral student Alex Gottlieb used a range of climate model simulations to look at snow accumulation across major watersheds in the Northern Hemisphere over a 40-year period starting in 1981. This allowed them to compare outcomes both with and without an increase in greenhouse-gas concentrations in the atmosphere due to fossil-fuel emissions.
They also compared these results with real world data, using direct measurements of snowpack at specific locations and estimates based on temperature and precipitation records.
In general, snowpack is harder to track than snow cover, because it varies so much across different regions and terrains. In some cases, ground-based and satellite measurements can be contradictory. The study authors sought to resolve those inconsistencies through various means, including by focusing only on snowpack during the month of March for each year.
“March in particular is nice because across most of the hemisphere that’s generally the peak of the snow season, when you’ve accumulated about as much as you’re going to, and then it starts melting out,” Mr. Gottlieb said.
Snow long
Human-caused climate change has led to a significant loss of spring snowpack at mid-latitudes across the Northern Hemisphere. Here the difference over a 40-year period is shown for individual watersheds associated with major rivers.
Per cent change per decade (1981–2020)
Decrease
Increase
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5%
NORTH AMERICA
EUROPE AND ASIA
the globe and mail, Source:
dartmouth college
Snow long
Human-caused climate change has led to a significant loss of spring snowpack at mid-latitudes across the Northern Hemisphere. Here the difference over a 40-year period is shown for individual watersheds associated with major rivers.
Per cent change per decade (1981–2020)
Decrease
Increase
-10%
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5%
NORTH AMERICA
EUROPE AND ASIA
the globe and mail, Source: dartmouth college
Snow long
Human-caused climate change has led to a significant loss of spring snowpack at mid-latitudes across the
Northern Hemisphere. Here the difference over a 40-year period is shown for individual watersheds associated
with major rivers.
Decrease
Increase
-10%
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5%
Per cent change per decade (1981–2020)
the globe and mail, Source: dartmouth college
The results show that climate change is having an effect on snowpack, but one that is highly non-linear. For example, in places that are sufficiently cold the effect is small because temperatures rarely rise above 0 degrees in winter. However, at mid-latitudes, particularly in Central Europe, the northeastern U.S., the southern Rocky Mountains and the Great Lakes region of Canada, the effect is pronounced. There, decreases in snowpack amount to 7 to 10 per cent per decade.
This means that more precipitation is falling as rain rather than snow in those regions – and the implications for water management in those locations could be profound, Dr. Mankin said.
“We’ve hard-coded our water management infrastructure to the expectation that a substantial fraction of the water originating within a river basin is going to be stored for some period of time as snowpack,” he said.
For example, in California last spring officials had to release water from swollen reservoirs because of rain in the mountains, even while knowing that water could be in short supply during hot, dry periods later in the year.
The change in snowpack also affects the natural environment by altering when and where nutrients are conveyed through watersheds each year, Dr. Mankin added.
Ultimately, the study found that snowpack has been resilient in places where average winter temperatures are below -8 degrees. Some Arctic areas have actually seen an increase in snowpack – an effect that can be attributed to more open water on the Arctic Ocean owing to a loss of sea ice. In places were global warming is pushing above the -8 degree threshold, change is under way and poised to accelerate with each upward bump in temperature.
Paul Kushner, an atmospheric physicist at the University of Toronto who was not involved in the study, said the authors had done a good job of wrangling diverse data sets to provide a more coherent picture of what is happening to snowpack around the hemisphere.
“The threshold of -8 degrees is a plausible indicator of where some real sensitivity lies,” he said, adding that projections for various Canadian regions could change quickly as new data on the rate of warming come in.
Dr. Mankin said that even with the variable at play in the analysis, the study offers a warning for many locations that it is time to plan for a very different water regime due to an anticipated loss of snowpack.
“Once we can detect it via the methods we advance here, it’s kind of too late,” he said. “You’re no longer in an anticipatory state, you’re in a crisis management state.”
Mr. Gottlieb said that in future work he intends to focus more directly on the economic implications of changing snowfall patterns, as large swaths of the Northern Hemisphere shift to an increasingly snowless future.