‘The treeline is out of control’: how the climate crisis is turning the Arctic green

2022-01-24

Excerpt from this story from The Guardian:

As the planet warms, the Arctic treeline is accelerating towards the pole, turning the white landscape to green. The trees used to creep forward a few centimetres every year; now they are leaping north at a rate of 40 to 50 metres a year. In the European Arctic, the birch is the leader of the pack.

Downy birch is one of few broadleaved deciduous trees in the Arctic and it is hardier even than most conifers. Its “down” is a soft coating of hairs that acts like a fur coat in the punishing cold. Often found cooperating with pines and spruce at lower latitudes and altitudes, above a certain point the birch leaves the others behind and goes on alone for hundreds of miles.

It might be unprepossessing, even ugly, with its stumpy branches and pockmarked bark, but this tough little tree is a survivor and a pioneer, essential to nearly all life in the Arctic. Used by humans for tools, houses, fuel, food and medicine, it is home to microbes, fungi and insects central to the food chain, and it is critical for sheltering other plants needed to make a forest. The downy birch dictates the terms of what can grow, survive and move in the areas in which it takes hold. And, as the Arctic heats up, that range is expanding fast.

Once upon a time, the first snows of winter would fall some time in October, initially on the tundra, the plateau above the treeline, and then on the pine and birch forests of the river valleys and the coasts. Shortly after, the mercury in the thermometer would descend below freezing and stay there until April or May, when the snow would begin to melt and the rivers would rush with the clear turquoise of superoxygenated ice. Until 2005, the average winter temperature in the region was -15C and it would reliably sink below -40C at least once during the winter, eliminating even the hardiest of all insect larvae, a process that kept the Arctic pest-free in the summer.

This world of winter was dark and cold and dry. At those temperatures there was no moisture at all. The snowpack was the consistency of sand, made up of several layers of large snow crystals. At -40C or-50C in the middle of winter, the quality and nature of snow crystals is critical to the survival of humans and animals alike.

When the temperature climbs back up towards zero or, even worse, above it, this delicate winter ecosystem collapses. Even a little warming of the snow can create havoc. Moisture starts to appear in the snowpack at -5C or -6C, at which point it loses its sand-like quality, and the snow starts to compact under the reindeer’s hooves, ruining the grazing beneath. If the thermometer goes all the way into the positive, as it has done increasingly in recent years, it is a catastrophe. Melting snow or rain will freeze when the temperature goes negative again, forming a crust of ice over the ground, locking the vegetation away from the browsing reindeer. This happened in 2013 and again in 2017. Tens of thousands of reindeer died; some herders lost more than a third of their animals.