The importance of snow
28 February 2019
The future of snow is inextricably linked to the destiny of Arctic flora and fauna. Most plants and animals in the Arctic tundra depend on favourable snow conditions to survive. For example, many require late-lying snow cover to overwinter, and large herbivores like reindeer can’t reach their food if the soft snow packs are replaced with hard ice layers. PEKKA NIITTYNEN explains why for many species, less snow may be an even greater threat than rising temperatures.
THE ARCTIC TUNDRA is a winter wonderland where the snowy season prevails. Traditionally, the snowpack has left the ground exposed to sun for only a few months of the year—sometimes only for several weeks. Some years, summer fails to arrive entirely. The Arctic tundra has always been a mosaic of different snow habitats.
However, this is changing rapidly because snow conditions are sensitive to even the smallest changes in climate. In some Arctic areas, increased winter precipitation may still somewhat compensate for the effects of rising temperatures on snowpack thickness. But in many regions—including my study areas in northernmost Scandinavia—the reduction in the length of snow season has been dramatic. In fact, the season has shortened by as much as three weeks in just the last 40 years. Year-to-year variations are large, but the trends are clear: long-lasting snow cover is vanishing across the northern hemisphere.
In the Arctic, where vegetation creeps along the ground and nearly everything is covered by snow for most of the year, the thickness of the snowpack is the most important modulator of ground surface temperatures. With only a very thin layer of snow, the ground surface temperature can be freezing, but under a metres-high snowpack, the thermal environment is stable and mild.
I am involved in a research project investigating how the changes in temperature and snow cover duration are likely to affect the extinction risk for northern flora. The results so far show that many species may actually benefit from a warmer climate if snow conditions remain as they are. But since the warming will most likely reduce the amount snow, it may wipe out a large part of the flora that are typical to Arctic mountains, such as snow buttercup and mountain brook saxifraga.
Although the significance of snow is widely recognized, winter conditions are often ignored in studies of the Arctic
areas. This may seem surprising, but the reason for this shortcoming is practical rather than ideological: gathering data on winter conditions from remote Arctic areas is extremely challenging. Polar nights and freezing temperatures do not tempt researchers to step outside, and the harsh conditions are a true trial for the research equipment.
We have tackled these practical difficulties by using satellite imagery and hardy miniature logging devices. Satellites have provided us with detailed information about Arctic snow conditions since the 1970s. What researchers need most is patience to process the massive datasets and computers with plenty of power and memory. Small temperature loggers have proven themselves weather-proof in the harsh Arctic winter conditions. As long as reindeer and lemmings leave the loggers untouched, they offer in-situ data to validate the satellite record.
Thanks to remote sensing and species distribution models, we know that winter and snow are hugely significant for the future of northern nature and organisms. Many Arctic and mountain plants grow and flower during very short summers. If the snow cover duration shortens and summers lengthen, the more southern species will benefit and could compete with Arctic species for survival, leading to the extinction of some Arctic species.
Mountain avens and glacier buttercups, two iconic Arctic flowering plants, require very different snow conditions, but both are very much affected by these changing conditions. Mountain avens would benefit from a shorter snow season, but the increasing temperatures will be a drastic disadvantage. Conversely, glacier buttercups require a thick snowpack. Vanishing snow cover will wipe the species out, especially its southernmost populations.
The problem is we don’t know exactly how the snow will change as the climate warms or what the Arctic snow conditions will be like if we succeed in limiting global warming to 1.5°C or 2.0°C. We can predict temperatures fairly accurately, but it’s more difficult to predict rainfall—and even more difficult to predict snowfall. Our study shows that depending on the rate of change in snow conditions, the snow will either buffer or speed up changes in Arctic biodiversity. Either way, the uncertainty is certainly frustrating.
PEKKA NIITTYNEN is a doctoral candidate at the University of Helsinki in Finland. His research focuses on the interactions between snow and plants in the changing Arctic.
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