Boreal forests are located in the cold climates of the high latitudes of the Northern Hemisphere. They lie just south of the Arctic tundra, where tree growth is restricted by year-round freezing or near-freezing temperatures and a lack of rain. Known as “taiga” in Russia, boreal forests are characterized by species that can cope with the cold, such as pines, spruces and larches. As the map below shows, they cover large parts of North America, Northern Europe and Asia.
Boreal forests are the largest biome, or ecosystem on the Earth’s land surface and account for 30% of the world’s forests. They are a very important carbon store. The exact amount of carbon stored in them is very uncertain, but estimates suggest that it is more than one-third of total terrestrial carbon.
Why is the boreal forest a tipping point?
The boreal zone and the trundra are warming approximately twice as fast as the global average. This study explains that continued temperature increases could lead to rapid changes in boreal forests, including dieback. It states that increasingly warmer summers are becoming too hot for the current predominant tree species, leading to increased susceptibility to disease, lower reproductive rates and more frequent fires. All this leads to a significantly higher mortality rate of trees. Increased tree mortality would lead to the emergence of large regions of open woodlands and grasslands, which would promote further regional warming and increased fire frequencies, triggering a strong positive feedback mechanism.
Where is the tipping point of the boreal forest?
The IPCC’s 1.5°C report states that a potential tipping point is between 3°C and 4°C of global warming above pre-industrial levels. However, given the complexity of the various forcing mechanisms and feedback processes, this is considered a rather uncertain estimate.
What would happen if we crossed the tipping point?
An extreme fire event or repeated severe events render the southern portion of the boreal forest incapable of regenerating as a forest ecosystem, and instead result in a conversion of the system to a grassland ecosystem. But while trees at the southern edge of the boreal zone risk dieback, research suggests that forests on the northern edge may expand into the tundra as climate change continues. There is evidence that this shift to the north is happening already. Similarly, shrub tundra is expanding into colder regions as a result of warming, and this process will continue. As a result, vegetation albedo will decrease — especially in spring — which will locally amplify warming. This would lead to increased heat absorption in the Arctic and faster thawing of the permafrost. Carbon and methane emissions from thawing permafrost and forest dieback on the southern edge of the boreal biome would be a double disaster and accelerate climate change.