But not enough to stop climate change.

Wooded areas and similar ecosystems are considered to be one of the planet’s most important carbon sinks. That’s because plants absorb carbon dioxide from the atmosphere during photosynthesis. In recent decades, humans have been pushing more carbon dioxide into the atmosphere. And so a pressing question arose among scientists. Because how do plants react to this? Could it mean that they may also be sucking up more carbon dioxide?

Photosynthesis

By the term “photosynthesis,” researchers refer to the process by which plants use sunlight to convert CO2 into carbohydrates that they can use to grow. During photosynthesis, plants open small pores on their leaf surfaces to suck carbon dioxide from the air and produce their own food. In a new study, researchers decided to map the extent to which plants accelerate photosynthesis in response to increased CO2 concentrations in the atmosphere. “That magnitude is really important to understand,” said study leader Trevor Keenan. “Because if the increase in photosynthesis is small, plants may not be the carbon sink we expect after all.”

More about carbon sinks
Carbon sinks refer to dynamic (permanent or temporary) storage sites of CO2. The stored CO2 then – temporarily or permanently – no longer contributes to climate change. For example, you should think of a growing forest (because it grows, it dynamically captures CO2, in contrast to, for example, a fully-grown forest that is not called a carbon sink, but a carbon reservoir). The largest carbon sink on Earth is the ocean. Nearly 40 percent of the CO2 released into the atmosphere from the combustion of fossil fuels since the industrial revolution has been absorbed by the ocean.

Using nearly three decades of estimates from carbon sinks, satellite images and models of the carbon exchange between the atmosphere and land, the researchers were able to determine the extent to which plants respond to the increased CO2 concentration in the atmosphere.

More CO2

And guess what? Plants nowadays extract much more CO2 from the air. The researchers find that the photosynthesis rate of plants increased by as much as 12 percent between 1982 and 2020. During the same period, the global atmospheric CO2 concentration increased by about 17 percent. That 12 percent increase translates into 14 petagrams (one petagram equals 1,000,000,000,000,000 grams) of additional carbon taken from the atmosphere by plants each year; that is roughly equivalent to the CO2 emitted worldwide in 2020 alone from the combustion of fossil fuels.

Climate change

It may seem like good news. But the researchers have an important caveat. Not all CO2 that is removed from the atmosphere through photosynthesis is stored permanently. “That 12 percent is a very large increase in photosynthesis,” Keenan says. “But it doesn’t remove the amount of carbon dioxide we pump into the atmosphere. So it doesn’t stop climate change in any way. It just helps us slow it down.”

For that reason, the study emphasizes the importance of protecting ecosystems that currently play an important role in slowing climate change. Keenan notes, however, that it is still unclear how long forested areas will help us with this. “We don’t know what the future holds,” he says. “For example, we don’t know whether plants will continue to respond to increasing carbon dioxide. We expect it to stabilize at some point. But we do not yet know when and to what extent.”