We depend on plants for necessities including food, water and medicine.
Now, research shows we might have plants to thank for giving us some much-needed help in slowing the rate of global warming.
Humans have continued to pump increasing amounts of carbon into the atmosphere. Since the 1950s, the rate at which carbon dioxide was accumulating in the atmosphere had climbed steadily. It surged from 0.75 parts per million per year in the 1950s to 1.86 ppm per year in 1989. But from 2002 to 2014, the rate stagnated, holding steady at around 1.9 ppm per year. (However, the overall concentration of atmospheric CO2 did rise over this period— just not as quickly as one might’ve expected it to.)
A study published in Nature Communications last month suggests the reason for this is that as CO2 levels have risen, plants have been ramping up photosynthesis and, therefore, absorbing more carbon dioxide than usual.
More photosynthesis has also meant more plants, which have in turn absorbed more CO2 and so on. For several years, this so-called “greening” of the planet is believed to have helped slow the rise of carbon in the atmosphere.
“These results are very exciting,” lead author Trevor Keenan, an ecologist at Lawrence Berkeley National Laboratory, told PRI’s Living On Earth podcast in a December interview. “We’ve known for decades that ecosystems have been taking up a lot of the carbon dioxide we emit into the atmosphere. Now, they are not taking up near enough to really stop climate change, but they are slowing it down significantly.”
Without the help of plants, the concentration of atmospheric carbon dioxide would be far higher than it is today, according to Keenan. In September, CO2 levels reached a daily average of above 400 parts per million for the first time in history. We’d already be at 460 ppm if not for the greening effect, a level “we don’t expect until about 2050 or 2060,” Keenan said.
But researchers warn this effect is only temporary and will soon start to wane (if it hasn’t already).
That’s because though plants take in carbon dioxide through photosynthesis, they also release CO2 through a process called respiration, which is sensitive to temperature increases.
“So, as CO2 is going up, plants take more CO2 from the atmosphere,” Keenan told PRI. But as global temperatures rise, plants will “also release more CO2.”
“We expect temperatures to continue to increase in the future and they already have over the past two years with the large El Nino event we’ve seen globally, and the net effect of this is a release of carbon dioxide,” Keenan added. “A lot of carbon goes into soils, and these soils are respiring ... [A]s temperature rises, that carbon that has been stored there could be released back into the atmosphere.”
Ultimately, Keenan stressed that though the research offers “good news for now, we can’t expect it to continue,” he told The Washington Post.
The study should, instead, serve as a reminder of how important it is to protect carbon sinks ― forests, oceans and other natural environments that help absorb CO2 from the atmosphere. Oceans and land plants help remove about 45 percent of the CO2 emitted by humans every year, according to a 2015 study.
It should also be another wake-up call for people to immediately reduce our greenhouse gas emissions. “The growth of CO2 in the atmosphere continues to grow. And until we really cut our emissions, that’s what’s going to continue to happen,” Keenan told The Verge.
“So plants are helping us out, they’re buying us time, but ultimately it’s up to us.”