World's forests increasingly taking up more carbon

The world's forests are increasingly taking up more carbon, partially offsetting the carbon being released by the burning of fossil fuels and by deforestation in the tropics, according to a new study.

Tropical forest. Photo: Antoine Cupial/Wikimedia Commons (CC BY-SA 4.0)

The findings suggest that forests are growing more vigorously, and therefore, locking away more carbon. Even so, the concentration of heat-trapping carbon dioxide in the atmosphere is still on the rise.

Every decade, Earth's forests are taking up carbon faster than the previous decade. The same is true of the oceans. Even together, the ocean and the land are not keeping up with industrial carbon emissions, and the global concentration of carbon dioxide in the atmosphere is rising at an accelerating rate.

The increased plant growth in global forests could be due to several factors, including higher concentrations of carbon dioxide in the atmosphere, warmer temperatures and increased availability of nitrogen.

The new study also contributes to a mounting body of evidence that tropical forests might take up more carbon -- and northern temperate forests might take up less carbon -- than many scientists once thought.

The study relies on a synthesis of results from "inverse transport models"-- atmospheric models run in reverse.

Scientists input the "results" -- the actual levels of atmospheric carbon dioxide measured worldwide during the past several decades -- and force the models to predict how much carbon dioxide must have been emitted and re-absorbed in different regions to match the measurements.

The new study finds that, averaged over the past decade, the carbon flux in the tropics is about zero -- meaning the additional amount of carbon being released by deforestation (an estimated 1.5 billion metric tons a year) is being compensated for by increased uptake in the remaining forest.

This capacity of intact forests to act as carbon sinks suggests that additional carbon dioxide in the air may be fertilizing those forests, allowing them to grow and store carbon more quickly, although changes in precipitation, temperature and deforestation could also be playing important roles.

The researchers said it isn't clear how long Earth's land areas will be able to keep increasing carbon uptake in the face of ongoing deforestation and continued emissions of fossil fuels. (National Science Foundation)

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