The greening of the Arctic

The Arctic is warming at four times the rest of the planet. As the Arctic warms and the climate changes, tundra ecosystems are in transition. But exactly how tundra ecosystems are responding as the climate warms is the big question that I have been addressing across my career. I have been exploring the ‘greening of the Arctic’, a phrase encompassing the increasing greenness at high latitudes that satellites have observed from space and the greater plant growth from long-term monitoring records on the ground.

In the Arctic, plants are greening up earlier and certain species are taking advantage of the warmer summers, expanding their green to cover the once bare ground. With warming we see an increase in plants, including an increase in certain types of species such as shrubs, grasses and sedges. Shrubs – the trees of the tundra – record their growth each year in their wood, and these shrub rings tell us that shrubs grow more in warmer summers.

On first telling, the greening of the Arctic seems like a straightforward scientific story – the Arctic warms and the plants grow more but with accelerating warming there is real urgency to untangle the connections between climate change and tundra ecosystems. However, the more we study these ecosystems the more complexity is revealed.

A key aim of my research is to figure out what the changes that satellites see from space mean in terms of change on the ground at sites around the Arctic. The satellite pixels of the decades-long satellite records are as big as swimming pools, football pitches or city parks, but a lot of the change that is going on in tundra ecosystems is happening at much smaller scales. Satellite observations can give us a misleading picture of the rates and magnitudes of change, missing both the most rapid rates of vegetation change and the increasing permafrost disturbances turning the green tundra brown, one of the suite of disturbances collectively referred to as Arctic browning.

As tundra plants respond to warming, the tundra’s thin layer of green becomes thicker, trapping a deeper blanket of snow insulating frozen ground from the winter’s cold and promoting permafrost thaw. And with thaw exposing the permafrost’s frozen soils, carbon is released, accelerating climate change for the planet as a whole.

As the Arctic warms, cold-loving species need to adapt to the warming Arctic. Treelines are inching northward and shrublines are on the move even more rapidly. As the tundra becomes more shrubby, boreal forest species such as moose and beavers expand their range northward. Migratory animals like caribou alter their migratory behaviour as habitats shift and the climate warms. The precise timing of pollinators and breeding birds could be upset by changes to the timing of plant growth.

Ultimately, Arctic greening influences not only tundra plants, but entire food webs and the livelihoods of Arctic people.