This year, the Arctic is experiencing the worst wildfires on record, with massive blazes in Greenland, Siberia and Alaska. And the frequency of wildfires around the world is expected to increase further as carbon emissions continue unabated. But there is some good news, at least. Charcoal produced by wildfires could ‘lock away’ a considerable amount of carbon for years to come, according to a new paper published on 5 August in Nature Geoscience (1). And could, therefore, be considered “a mechanism for longterm carbon sequestration”, thereby mitigating some of the effects of human-induced climate change.
On average, wildfires burn 3–5 million square kilometres of the Earth’s surface annually — equivalent to almost half the land area of Europe — and add more carbon dioxide (CO2) to the atmosphere (2.2 Pg of carbon per year) than the global road, rail, shipping and air transport industries combined. But just how much carbon is actually being sequestered as a result of these wildfires?
“CO2 emitted during fires is normally sequestered again as vegetation regrows, and researchers generally consider wildfires to be carbon neutral events once full biomass recovery has occurred”, explains lead author Dr Matthew Jones of Swansea University. This new vegetation effectively provides a “sink” of carbon sequestered by photosynthesis on timescales that more closely resemble those of anthropogenic — or human-induced — climate change, instead of the typical millennial time-scales.
In grasslands, CO2 recovery can take less than a year. Whereas, in fire-adapted forests, can proceed over decades. And in arctic or tropical peatlands, full recovery may be more like centuries. However, carbon that is not reabsorbed by vegetation remains in the atmosphere and contributes to climate change. In this way, deforestation fires, in particular, can result in long-term loss of carbon to the atmosphere, and therefore, act as a significant contributor to climate change.
On the other hand, unburned vegetation is transformed into carbon-rich charcoal that ends up in soils and oceans for centuries — even millennia — to come. So, the team of researchers from Swansea University and Vrije Universiteit Amsterdam set out to quantify the critical role of this so-called pyrogenic carbon — charcoal created by fires — in helping buffer carbon emissions produced by forest fires. To do this, they combined field studies, satellite data, and computer models to better quantify the amount of carbon taken up after fires on the global scale.
The researchers found that globally, the production of pyrogenic carbon is equivalent to 12 per cent of CO2 emissions from fires and can be considered a significant buffer for landscape fire emissions. In other words, landscape fires transfer a considerable portion of carbon into charcoal and other materials. Therefore, pyrogenic carbon is important and should be considered in global fire emission models, the authors say.
Climate change is viewed as the great “threat multiplier”. The growing frequency of wildfires, as well as flooding, heatwaves, and drought is certainly evidence of these compounding phenomena. In particular — and if this year is anything to go by — wildfires are expected to increase the overall atmospheric CO2 emissions in the future.
But this will also have a corresponding impact on pyrogenic carbon storage. And if vegetation is allowed to recover naturally, emitted CO2 could be recaptured by regrowth in future decades, leaving behind an additional stock of pyrogenic carbon in soils, lakes and oceans.
So, in essence, the researchers have uncovered some good from the bad. Of course, more research is still needed. Nonetheless, pyrogenic carbon production is clearly an important element of the global carbon cycle.
(1) Jones, M.W. et al. Global fire emissions buffered by the production of pyrogenic carbon. Nature Geoscience (2019). DOI: 10.1038/s41561-019-0403-x