Fire and ice: Impacts of wildfires on permafrost and peatlands

A big impact of fires is that when burned, peatlands and permafrost release large amounts of carbon they store back into the atmosphere. We have actually measured the age of the carbon dioxide emitted from the peat. There's some evidence that suggests that even though wildfires may burn to a depth of only 15-20 centimeters, the warming starts to transmit further down into the deeper peat column. And even if it's just slightly warmer temperatures, it increases the rate of carbon loss beyond the burned area in deeper but still unfrozen peat. It's not causing massive loss in the deep layers, but it's waking them up and making them more sensitive to temperature changes. So there are some minor signals that fire disturbance actually increases deeper carbon losses.

There's also impacts due to the dynamics of changing snow cover. Snow coverage is a bad thing for permafrost because it insulates the peat layer during the coldest part of winter, [sheltering it from freezing temperatures that reinforces the permafrost]. Trees are good at intercepting snow fall on the ground, so when fires burn off trees in permafrost areas, snow is able to cover the permafrost and acts like a thick blanket keeping the cold away. So it's not only warmer in the summer, it's also warmer in the winter.

Permafrost thaw can also have a profound impact on air quality. When peatlands burn, they smolder and there's a lot more particulate matter produced compared to burning trees. This has a huge impact on air quality in northern Canada, especially because many people in this region don't have air conditioning and are used to keeping their windows open all summer long.

To flip the script, there's also impacts of permafrost loss on fire. After fire, we go from this relatively dry tree system on top of the permafrost to a sort of soup of wet mosses from the thawing ground ice. So ironically, fire on permafrost peatlands can breed a wetter ecosystem in its wake. If you fast forward to 20 or 30 years following a fire, these previously burned peatlands that are now much wetter environments could serve as a barrier to new fire. What we're seeing now with this accelerating fire cycle is that in peatland permafrost, fires aren't moving nearly as fast as they did when the landscape had mature timber on it. Nature is finding a little way to push back and slow down these fires.