Recent data from the Intergovernmental Panel on Climate Change estimate that carbon dioxide (CO2) concentrations in the atmosphere have risen close to 40 percent since before the industrial revolution. The effects of this rise on climate, sea levels and human societies are still being modeled, but one long-standing mystery for scientists has been how plants respond to rising CO2 levels, and how their ability to store the greenhouse gas feeds back into the carbon cycle.
UC Merced environmental engineer Elliott Campbell thinks he’s uncovered some answers, and he found them in an unusual place: ice samples taken from Antarctica. His research recently appeared in the research journal Nature, and the story was subsequently picked up by the New York Times. Below are a few excerpts from his Skype conversation with reporter Kerry Klein.
“One of the big questions right now with climate change is understanding how the plants will interact with climate change,” Campbell says. “To some extent, we expect plants to be impacted, to suffer from climate change; and to another extent we expect plants to help try and mitigate climate change, try and slow down the pace of climate change. That’s really what inspired this study: To try and understand at a global scale how the plants might respond.”
Many studies in this field have been designed around experimentally raising CO2 levels near a particular ecosystem and examining how it responds. But Campbell says he and his colleagues wanted a glimpse of the bigger picture.
“We did something called a natural experiment,” he says. “We looked at how the world has essentially changed over the last several centuries to try and understand how it might change in the future.”
How did they do it? By measuring atmospheric levels of carbonyl sulfide, a gas molecule that plants take in during photosynthesis. It’s “a proxy, kind of like a shadow that’s cast by plants as they grow but it’s in the atmosphere,” Campbell says. “Think of it as a cousin of CO2. It’s very similar in its makeup and that’s why plants take it up.” Generally speaking, the less carbonyl sulfide is in the atmosphere, the more actively plants are photosynthesizing and growing.
Campbell obtained the carbonyl sulfide data from partners who have collected and analyzed ice cores from Antarctica.
“Folks from NOAA and UC Irvine have been making measurements in Antarctica, in a place where no plants grow,” Campbell says. “But when you make measurements in the ice and the snow in Antarctica, you get a record of previous atmospheres, of what the atmosphere looked like 50, 100 or even thousands of years ago. What we did was go in and try and interpret, try and understand what those measurements were telling us about the plants.”
“We found that the only to explain the historical measurements from that ice and snow is if plants were growing faster and faster every year, in fact growing about 30% faster than they were 2 centuries ago, before the industrial era.”
According to Campbell’s findings, as atmospheric CO2 levels increase, plants up their game and grow faster so they can absorb more of the greenhouse gas. Without this increased activity, Campbell says, atmospheric CO2 levels would likely be even higher today.
So can we count on plants to continue buffering against climate change into the future? Campbell says scientists are wondering that, too, but they know not to be overly optimistic.
“We know from the historical period now that the plants are growing faster and faster; they’re taking up more and more CO2. In fact, that same type of process is in our climate change projections. So right now we kind of assume going into the future that the plants will continue to provide this service, and that’s what all our forecasts of climate change are based on. But there is an open question: If the plants run out of the nutrients or water or some other limiting factor, maybe they won’t be able to do this anymore.
“The bottom line, though, is that even with this service plants are providing, we’ve essentially overwhelmed this safety mechanism. The rate at which we put CO2 in the atmosphere is unfortunately much faster than the plants can take it up.”
Listen to the audio above for the full interview.