Plants Have Been Slowing the Rate of CO2 Over the Past Decade

The increase in atmospheric CO2 levels slowed between 2002 and 2014 thanks to plant growth, but the surge in greenery can't keep pace with rising emission levels.

Humans have contributed to the acceleration of CO2 levels in Earth's atmosphere for centuries, but a recent surge in plant growth caused this acceleration to slow down for over a decade.

A study published in Nature found that the growth rate of atmospheric CO2 "paused" from 2002 to 2014, which they attribute to an increase in plant life that "breathe" some of our CO2 emissions.

Several recent studies have shown that planting trees and other vegetation can improve air quality by scrubbing it of particulate pollution and capturing carbon. This is essentially what the vegetation in the terrestrial biosphere sink did from 2002 to 2014. During this period, the amount of CO2 caused by human activity still increased, but an increase in the plant growth of the terrestrial sink allowed more of that CO2 to be captured, which prevented it from being released into our atmosphere.

During photosynthesis, plants turn water, sunlight and CO2 into glucose. An increase of CO2 in the atmosphere means plants can photosynthesize faster, as long as they have enough water and nutrients.

Another reason for the slowing of CO2 growth during this period, as Carbon Brief explained, is that plants also respire during photosynthesis, a process that produces CO2 but is temperature-dependent. From 2002 to 2014, Earth's surface temperature was slower to rise, which slowed the process of respiration as well. More CO2 stayed locked up in our plants, trees and oceans rather than ending up in the atmosphere.

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While some might think this could mean that plants might save us from dangerous CO2 levels, unfortunately they simply can't grow quickly enough to compensate for our steadily increasing CO2 emissions, or for Earth's changing weather patterns.

Simone Aloisio, PhD, professor of chemistry at CSU Channel Islands, told Seeker he believes this study is good news in terms of how we understand climate change.

"A better understanding of the terrestrial biosphere sink is critical to understanding what to expect in the future," he said. "The overall picture though, as the authors point out, is that the pace and magnitude of climate change is still most dependent on CO2 emissions from the burning of fossil fuels."

Since the mid-1850's, once we began burning fossil fuels and making cement, atmospheric CO2 has steadily risen. Before industrialization, the atmospheric concentration of carbon dioxide was 280 parts per million (ppm). In 2016, heightened by weather patterns from El Niño, that number stayed above 400 ppm all year for the first time ever.

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Essentially, Earth's vegetation has been playing defense against the damaging effects of global warming for decades, but it hasn't changed the fact that CO2 levels are continuing to rise at a rapid pace. Also concerning is that the recent effects of El Niño have caused a weakening of the carbon sink, and as temperatures continue to rise, the way plants and trees use CO2 could be disrupted as well.

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"The study looked at how the terrestrial biosphere sink increased with increased levels of atmospheric CO2, [but] there are other sinks and sources that will also be affected as CO2 increases, temperature increases, and rainfall changes," Aloisio told Seeker.

"So, while this study points to a compelling reason why global warming was somewhat mitigated recently, I don't think we can jump to the conclusion that it will continue to be mitigated as the atmospheric CO2 levels increase. The best way to defend our planet against increasing CO2 emissions remains reducing those emissions."