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For 12 years, plants bought us extra time on climate change

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Reducing emissions is still key

Rainforest in Tasmania’s Hellyer Gorge
Wikimedia Commons

Plants are our best friends in the fight against climate change, and a new study shows just how important they are. From 2002 to 2014, plants sucked up so much carbon dioxide that they slowed the buildup of CO2 in the atmosphere, even as human-made CO2 emissions were increasing.

The findings, published this week in the journal Nature Communications, show how important ecosystems are in regulating the carbon cycle, and also how little we know about the processes contributing to climate change. This information can help scientists and policymakers come up with solutions to mitigate greenhouse gas emissions.

“That’s a big issue because you can’t design an effective strategy if you’re using something that you can’t predict,” says study co-author Trevor Keenan, a scientist in the Climate and Ecosystem Sciences Division at Lawrence Berkeley National Laboratory.

We already knew that oceans and land plants remove about 45 percent of the CO2 emitted by human activities each year. And the amount of CO2 that’s removed has more than doubled in the past 50 years. With plants, which need carbon dioxide to grow, that’s because CO2 increases photosynthesis. So more CO2 in the atmosphere means plants also absorb more CO2. But that doesn’t mean we’re fine pumping the greenhouse gas into the air.

In fact, more CO2 means warmer temperatures, and warmer temperatures cause ecosystems — plants, trees, and even bacteria in soil — to release more CO2 back into atmosphere. So it’s a give and take.

But the study authors realized something they didn’t expect: between 2002 and 2014, the CO2 concentration in the atmosphere wasn’t going up even though people were emitting increasing amounts of carbon dioxide. After analyzing climate measurements and simulations, they figured out that the “give and take” process had been altered.

While the buildup of CO2 in the atmosphere caused plants to absorb increasing amounts of CO2, something else happened that allowed the plants to keep storing this carbon dioxide. From 2002 to 2014, temperatures over global land were increasing but not as dramatically as in the decades before. So the slowdown in warming rates allowed the plants to absorb more carbon dioxide than they released — effectively slowing down the buildup of CO2 in the atmosphere.

“The extent of the acceleration of how much carbon dioxide they were taking up during this period was quite surprising,” Keenan says.

Though the findings seem like good news, they’re not really, Keenan says. The last two years have been the hottest on record, which means that the magic the plants were doing has probably already ended. The CO2 plants store is also not gone forever, Keenan says. As more ecosystems are in danger because of climate change, more plants and trees will die and will rerelease that carbon dioxide into the atmosphere. There’s no escape. And the only solution is to reduce the amounts of CO2 we emit in the first place.

“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 says. “So plants are helping us out, they’re buying us time, but ultimately it’s up to us.”