Plants Are Absorbing More CO2 From the Atmosphere Without Using More Water

Flora around the world are sucking up 17 percent more heat-trapping gas than 30 years ago — and appear to be doing it without increasing water consumption.

Trees, bushes, and other land-based plants are sucking up more carbon dioxide without a commensurate increase in water consumption, according to new research out of Australia that scientists claimed had major implications for modeling and preparing for climate change.

Jungles near the equator, piney northern forests, and other flora are absorbing 17 percent more carbon dioxide than 30 years ago, resulting in land plants acting as “sinks” for around 30 percent of the carbon in the atmosphere, said the study published July 24 in the journal Nature Communications. The oceans absorb another 25 percent.

It’s no surprise that plants would gobble up excess carbon dioxide in the atmosphere. Under natural conditions, humans and other oxygen-inhaling creatures breathe it out while plants breathe it in and exhale oxygen. But the buildup of greenhouse gases in recent decades have given plants even more to gobble up.

“All that carbon that instead of being respired back into the atmosphere stays with the plants until it goes back in the soil when the plant falls and decomposes,” said study coauthor Pep Canadell, a Canberra-based scientist at the Commonwealth Scientific and Industrial Research Organization and executive director of the Global Carbon Project.

Canadell and his colleagues showed that plants are becoming more efficient at using carbon dioxide to thrive while requiring less water by tightening tiny pores called stomata that permit gas to enter without letting water out, said Canadell. “The incredible finding is that plants are able to increase carbon uptake and create biomass and carbon stock in the biomass but with barely any extra use of water,” he said.

Canadell and his colleagues tracked carbon and water levels in forests around the world using atmospheric readings, satellite pictures of Earth and poles around 200 feet tall that put data recorders at the top of forest canopies around the world. They observed thicker forests and more woody encroachments on grasslands, he said. Carbon composes around 50 percent of plants, so more of it was helping the planet’s vegetation grow hardier.

“It’s really transforming, to some extent, the structure of the land’s surface,” said Canadell. “It’s becoming rougher. It's becoming denser. Forests are thickening. Plants are becoming more stems-per-hectare, or they are just getting bigger. From the carbon perspective, we are increasing the global carbon stocks on land.”

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The findings don’t predict a glut of water as a result of less thirsty plants, unfortunately. Instead, they suggest that even though plants are using less water individually, they often wind up drinking more water collectively over time as they flourish.

“There are more plants in the landscape because you now have more water to go around,” he said, explaining that this indirect effect of camel-like plants could spell big trouble for arid areas already struggling with droughts and other symptoms of climate change. “Where water is not plentiful, this can be a deal breaker.”

Climate change scientists had already factored plants storing carbon dioxide into their projections, so the findings also don’t mean plants would compensate for a new gas-guzzling car, either.

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They could help experts make more exact measures of climate change’s effects, however, said Canadell, who said his team would now look into exactly how much carbon and water plants might be saving and how climate change models might consider these new insights.

“We need to understand the good and bad of all these changes,” he said. “These are big numbers. We are talking about massive changes of carbon fluxes and water fluxes.”

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