Forests still offset half of global fossil emissions

The world’s forests, an American study notes, absorb between 3.5 and 4 billion tonnes of carbon each year. Equivalent to “nearly half of the carbon dioxide emissions from burning fossil fuels between 1990 and 2019.”

by Matteo Cavallito

 

Forests around the world are still an essential resource in climate change mitigation. This is confirmed by a new study by a group of scientists from a dozen countries. The investigation, which involved, among others, the Forest Service of the United States Department of Agriculture (USDA) and the Woodwell Climate Research Center in Woods Hole, Massachusetts, highlights in particular that despite the presence of established threats such as deforestation and fires, forest ecosystems have been absorbing carbon dioxide at a steady rate over the past three decades.

In the research, published in the journal Nature, the authors analysed data from millions of forest plots worldwide. That is, authentic ground measurements conducted on a random basis including trees that differ in size, species and biomass. The on field survey, which incorporates additional information from remote sensing, is precisely the most distinctive feature of the study.

Forests absorb 3.5 billion tonnes of carbon each year

“The uptake of carbon dioxide (CO2) by terrestrial ecosystems is critical for moderating climate change,” the research explains. “To provide a ground-based long-term assessment of the contribution of forests to terrestrial CO2 uptake, we synthesized in situ forest data from boreal, temperate and tropical biomes spanning three decades. We found that the carbon sink in global forests was steady, at 3.6 ± 0.4 Pg C yr−1 in the 1990s and 2000s, and 3.5 ± 0.4 Pg C yr−1 in the 2010s.”

This is, according to a Forest Service release, “nearly half of the carbon dioxide emissions from burning fossil fuels between 1990 and 2019.” However, “despite this global stability, our analysis revealed some major biome-level changes.”

Fires and deforestation are still a problem

Trends, in short, vary for the different ecosystems under study. The boreal forests of the northern hemisphere, which characterise the vast expanses of Alaska, Canada and Russia, for example, have shown a significant drop in their carbon absorption capacity, which has decreased by 36%. This phenomenon is mainly linked to an increase in fires, the spread of insects and soil warming.

Absorption in tropical forests is also declining: deforestation has caused a 31% decrease in their capacity to absorb carbon. However, the statement points out, regrowth in previously abandoned agricultural land and deforested areas has partially offset these losses. At the same time, temperate forests, on the other hand, experienced a 30 per cent increase in their ability to sequester the element. A result, the note emphasises, of extensive reforestation efforts, particularly in China.

Restoration of forested areas is crucial

However, the sequestration capacity, the scientists remark, is threatened by problematic phenomena. These include the ageing of the forest areas, continuous deforestation and the intensification of external activities that alter the balance of the ecosystem. Climate mitigation therefore requires land management policies that limit deforestation, promote forest restoration and improve timber harvesting practices.

“The persistence of the global forest carbon sink was a surprise given global increases in wildfire, drought, logging, and other stressors,” said Richard Birdsey, researcher at the Woodwell Climate Research Centre and co-author of the study.

“But it turns out that increasing emissions in some regions were balanced by increasing accumulation in other regions, mainly re-growing tropical forests and reforestation of temperate forests. These findings support the potential for improving protection and management of forests as effective natural climate solutions.”