Vast boreal peatlands may dry up and burn in a warming climate
Understanding peatlands accurately is critical to future climate models
Originally published on May 16, 2020.
Boreal peatlands around the world, including Canada's vast north, are important for storing carbon, but a new study suggests that climate change may slowly dry them. This could lead to persistent carbon releases and increase the risk of fires in peatlands as well as in surrounding forests.
The boreal forest covers a large parts of the northern terrestrial landscape, and about 15 per cent of it is peatland. However, the way that peatlands interact with the atmosphere has not been well understood. As a result, most global climate models make the assumption that the boreal landscape is entirely forest. This could mean they don't model the north accurately.
A new study led by Manuel Helbig, from the School of Geography and Earth Sciences at McMaster University, working with a team of nearly 60 scientists from around the world, may help change that.
Warm air may dry out peatlands
Peatlands are generally very wet areas in which the ground is saturated and mosses and shrubs build up on top of each other, so a thick layer of dead organic material is overlain by a living layer.
Helbig and his colleagues looked at the critical question of how fast peatlands will dry in a warming climate. Trees have adaptations to hold onto their water in warming conditions. But Helbig and his colleagues observed that because the mosses that make up the living layer of peat have no such mechanism, peatlands have no way of retaining water. As a result, in warmer conditions, increased evaporation can literally suck the water out of peatlands.
Observations of evaporation from stations in boreal landscapes around the world demonstrated this.
Where there's dry peat, there may be fire
As the peatlands dry, the living plants no longer absorb carbon, and the drying dead plant material decomposes, releasing stored carbon, which contributes to further warming.
This, according Helbig, is not the end of the story. Not surprisingly, drier peatlands may also burn more easily than wet ones, releasing more carbon dioxide. And wet peatlands tend to act as fire breaks in the boreal landscape. Drying peatlands will be less effective.
Climate models do suggest the possibility that increased rainfall will compensate for increased evaporation in a warmer climate. Helbig is concerned, however, that there may not be enough precipitation to keep pace with the rate at which peatlands are losing water due to warming temperatures.
Written and produced by Mark Crawley