Forests absorb more of our CO2 emissions but hardly enough

Forests worldwide are absorbing more CO2 from the air but they come up short when it comes to sucking up the vast amounts of CO2 emitted by humans into the atmosphere, researchers say.

In a newly published study, a team of scientists set out to estimate carbon fluctuations in northern and southern forests by the help of ample data and computerized climate models. Their results confirm earlier findings that forests do grow faster with increases in concentrations of atmospheric carbon.

Atmospheric CO2 aids plants in photosynthesis and so more CO2 in the atmosphere might, on the face of it, seem beneficial to forests. “Intact forests are playing a large role in absorbing the CO2 we’re emitting,” noted Benjamin Gaubert, the study’s lead author who works at the National Center for Atmospheric Research. “This means that global forest are helping to mitigate climate change or at least helping to mitigate the impacts of carbon emissions in the atmosphere.”

Yet even so the planet’s forests can capture only a fraction of human-caused emissions. Specifically last year they captured a total of 37.1 billion tons, which means that around 30% of annual carbon emissions are captured by forest growth globally. “Both the southern tropics and the northern temperate forests are taking up more carbon than in the past, but the amount being taken up by intact tropical forests was a particularly interesting revelation for the team,” Gaubert said.

Northern forests accounted for most of the CO2 absorption because they cover more landmass. However, tropical are most effective at trapping carbon, not least because of favorable weather conditions like year-long sunshine. “We found that carbon movements in the tropics were nearly neutral,” Gaubert said. “That was interesting for us because we know that rapid deforestation and urbanization would lead one to believe there would be more carbon outflows if [the forests] weren’t sequestering carbon faster than before.”

Troublingly, across the tropics, from Indonesia to Brazil, large swathes of forest are being cut down to make way for palm oil plantation, agricultural land and pastures for cattle.

Questions also remain about the effects rising concentrations of atmospheric CO2 will have on the planet’s forests, especially in tandem with rising temperatures brought on by climate change. According to another recent study, plants respond to more CO2 in the air by thickening their leaves by as much as a third.

This changes the ratio of surface area to mass in a leaf and affects a plant’s ability to perform such vital function as photosynthesis, evaporative cooling and sugar storage. Scientists are now working to find out how these physiological changes in plants might affect future climate models.