Boreal forests are key players in the global carbon cycle, because they store 30–40% of terrestrial carbon
1. They have been considered to be carbon sinks, mainly because they accumulate large amounts of carbon in the form of organic soils
2. Their net carbon balance is driven by natural wildfires (Fig. 1), which produce large carbon emissions approximately every 70 to 200 years
3, and which are necessary to maintain the productivity and biodiversity of these forests. But climate change is likely to shorten the period between fires (the fire-return interval) by producing warmer temperatures, more lightning strikes, longer wildfire seasons and drier forest conditions than those seen at present
4. In a
paper in Nature, Walker
et al.
5 show that the increase in fire frequency might turn boreal forests from carbon sinks into carbon sources.