Plants consuming more carbon dioxide to counter climate change

Berkeley Lab – Scientists have found that plants are consuming more carbon dioxide from the atmosphere than before, but they say it is only enough to delay climate change instead of stopping it.

An international team of researchers led by Lawrence Berkeley National Laboratory (Berkeley Lab) and The University of California, Berkeley have used a novel methodology combining remote sensing, machine learning, and terrestrial biosphere models to find that plants are indeed photosynthesizing more, to the tune of 12 per cent higher global photosynthesis from 1982 to 2020. In that same time period, global carbon dioxide concentrations in the atmosphere grew about 17 per cent, from 360 parts per million (ppm) to 420 ppm.

The 12 per cent increase in photosynthesis translates to 14 petagrams of additional carbon taken out of the atmosphere by plants each year, roughly the equivalent of the carbon emitted worldwide from burning fossil fuels in 2020 alone. While not all of the carbon taken out of the atmosphere through photosynthesis is stored in ecosystems, as much is later released back to the atmosphere through respiration, the study published in Nature reports a direct link between the increased photosynthesis and increased global carbon storage.

“This is a very large increase in photosynthesis, but it’s nowhere close to removing the amount of carbon dioxide we’re putting into the atmosphere,” said Berkeley Lab scientist Trevor Keenan, lead author of the study. “It’s not stopping climate change by any means, but it is helping us slow it down.”

Measuring photosynthesis

Because carbon dioxide stays in the atmosphere decades longer than other greenhouse gases driving global warming, efforts to reduce it are critical to mitigating climate change. Plants, through photosynthesis, and soils sequester roughly a third of carbon dioxide emissions released into the atmosphere each decade from the burning of fossil fuels.

Through initiatives such as AmeriFlux, a network of measurement sites coordinated by the Department of Energy’s AmeriFlux Management Project at Berkeley Lab, scientists from across the world have built over 500 micrometeorological towers in forests and other ecosystems to measure the exchange of greenhouse gases between the atmosphere and the vegetation and soil. While these flux towers can help estimate photosynthesis rates, they’re expensive and thus limited in their geographic coverage, and few have been deployed long-term.

Bringing history in the picture

Looking back at nearly three decades of carbon sink estimates made by the Global Carbon Project, Keenan and his team of researchers compared these with predictions from satellite images of the Earth taken between 1982 and 2012 and models using carbon exchange between the atmosphere and land to make carbon sink estimates.

“Our estimate of a 12 per cent increase comes right in the middle of the other estimates,” he said. “And in the process of generating our estimate, it allowed us to re-examine the other estimates and understand why they were overly large or small. That gave us confidence in our results.”

“We don’t know what the future will hold as far as how plants will continue to respond to increasing carbon dioxide,” he added. “We expect it will saturate at some point, but we don’t know when or to what degree. At that point land sinks will have a much lower capacity to offset our emissions. And land sinks are currently the only nature-based solution that we have in our toolkit to combat climate change.”

The study was supported in part by NASA and the DOE Office of Science.