You’ve probably seen dramatic images of out of control wildfires that directly and immediately affect people. The news recently followed 200 firefighters tackling a blaze in California, while this May many watched the evacuation of more than 50,000 people from Fort McMurray in Canada.
But, every so often, in regions too remote for the TV cameras, satellite images reveal vast fires covering thousands of square kilometres in smoke. This is what’s happening in Siberia, right now.
This all leaves an impression of large-scale destruction and ecological disaster. But are we really right to be worried?
Although – wrongly – perceived as avoidable disasters, wildfires have been a natural and fundamental part of many of the world’s forests, grasslands and shrublands for millions of years. Fire is part of a natural rejuvenation cycle in these ecosystems. Attempts to eliminate it can have negative ecological impacts such as loss of biodiversity or increased vulnerability of forests to disease, and simply increase the risk of larger, more catastrophic fires.
Although necessary for many ecosystems, wildfires do release vast amounts of carbon into the atmosphere, currently 1.6–2.8 gigatonnes a year, equivalent to a third of the total amount emitted from the burning of fossil fuels. The CO2 emissions from fires help accelerate global warming, which in turn leads to more fire, while soot emitted from fires is often deposited on ice leading to accelerated melting.
But that’s only part of the story. While burning vegetation inevitably releases carbon, this carbon is normally taken up again when the forest regrows. And charcoal formed during burning means carbon is “locked up” in soils and sediments. So wildfires in regions adapted to fire can overall be considered “carbon neutral” or in some cases even lead to carbon sequestration in the longer-term.
This means naturally recurring wildfires aren’t necessarily a threat to ecosystems or the global climate. What is of wider concern, however, is when they occur in ecosystems that are not well adapted to fire such as tropical forest or peatlands, or where fires are changing in their extent, or in how severely they burn the landscape. While the average annual area burned globally has changed surprisingly little during the last few decades, there are worrying trends in some regions such as larger blazes and longer fire seasons in the western US as a result of land management and a warming climate.
Considering all this, what about the current fires in Siberia? Are they really anything out of the ordinary – and what should we make of the concern raised by Greenpeace, that the Russian government’s official figures of area burnt are huge underestimations?
Satellite observations can help us answer these two questions. First, satellite data has long shown that Russian government statistics are substantial underestimations of actual ﬁre activity. Second, the annual area burned in boreal Asia (predominantly Siberia) is particularly variable, compared to the world’s other main vegetation zones. On average around 5m hectares have burned every year between 2001 and 2012, but this covered a range of more than than 15m in 2003 to less than 3m in 2005. The area burned so far this year in Siberia is well within that range, but then we’ve only just reached midsummer – the season is not yet over.
Just like boreal Canada, temperatures in Siberia are increasing faster than in many other parts of the world and this trend is expected to continue. Rising temperatures lead to drier vegetation, to fuel the fires, and more lightning, which increases the risk of fire. A hotter climate also lengthens the season during which fires occur. These factors combined are expected to increase fire activity in this region.
What is particularly worrying here is some of the fires in Siberia and other boreal regions affect peatlands which are gradually thawing thanks to global warming. This has a knock-on effect on the climate. When they burn deep into the ground peatland fires can release carbon that has accumulated over millennia and turn these peatlands from being net carbon sinks to long-term carbon emitters. So irrespective of discrepancies in reporting of fires in Siberia and the fact that fires are a natural feature of boreal forests, we can expect more fires and more associated greenhouse gas emissions in boreal regions in a warming world.