Despite regional threats such as deforestation and forest fires, the world's forests continue to be a powerful weapon in the fight against climate change. New research reveals that the world's forests have consistently absorbed CO2 over the past 30 years, averaging 3.5 ± 0.4 billion tonnes of carbon per year. This is more than a third of the emissions from burning fossil fuels between 1990 and 2019.
Forests still play a crucial role in mitigating climate change, this study shows. But in some places, there are also threats that reduce the storage capacity of forests or even make them a source of carbon emissions. In particular, boreal forests in the Northern Hemisphere (Alaska, Canada and Russia) have experienced a significant decline in their carbon sink capacity of 36%. This decline is attributed to an increase in forest fires, insect outbreaks and soil warming. Canadian forests are now even a small source of carbon emissions.
Neutral balance in the tropics, differences in temperate forests
Even in tropical forests, capture capacity is decreasing in some places. Due to deforestation, some regions absorb 31% less carbon. This loss is partly offset by regrowth of forests on former agricultural land and in cleared areas, so the net carbon balance remained neutral in the tropics.
European forests showed a small decrease in their absorption capacity, presumably due to the effects of climate change, increased timber harvesting and less investment in new and young forests. In contrast, other temperate forests are actually absorbing 30% more carbon. This increase is largely due to major forest restoration and reforestation efforts, especially in China.
Unique ground-based measurements
The research team analysed data from millions of forest plots around the world, combining measurements from forest inventories and remote sensing. Gert-Jan Nabuurs led the European part of the study together with Bas Lerink, both working at Wageningen University & Research.
"This study distinguishes itself because it is based on extensive ground-based measurements," explains Nabuurs. "Essentially a tree-by-tree assessment of size, species and biomass. These measurements are still the most reliable source of information. Remote sensing is important to assess tree cover from above, but cannot see the growth dynamics of a forest below. The unique value of this study lies in the detailed data collection on site."
Outcome surprise for scientists
"That the world's forests are still storing so much carbon was a surprise given the increase in wildfires, drought, logging and other stressors," Nabuurs says. "It now appears that increasing carbon emissions in some regions are offset by higher storage in other places. This is mainly due to the regrowth of secondary forests, reforestation and sustainable management of temperate forests. In the media, there is a lot of focus on threats such as forest fires, but as I sometimes put it: a falling tree makes more noise than 100 growing trees. This possibly explains the surprising outcome."
Forests as a natural climate solution
The findings support the potential of better forest management and protection as a natural climate solution. The research describes how certain policies can help maintain global carbon sequestration. For example, a focus on reducing deforestation in the tropics, forest restoration in degraded areas and where agriculture is not possible, improving timber harvesting and long-term use of wood to reduce emissions from logging. The European Nature Restoration Act is an essential response to this, according to the researchers, which now needs to be implemented consistently.
The study also cites limitations in data access and data collection, especially in Russia and tropical regions. The researchers call for more research and the establishment of forest inventories in these areas, and openness of data to reduce uncertainties in carbon estimates. This would make it possible to improve the global carbon balance.
