As carbon dioxide continues to build in the atmosphere — thanks to the burning of fossil fuels — scientists are busy figuring out how life on earth is adapting to its effects. And now, new research reinforces the idea that the world’s plant life is adjusting in a subtle, but deeply significant, way.

A study, just out Monday in the journal Proceedings of the National Academy of Sciences, supports a long-standing theory that some plants become more efficient at using water under higher carbon dioxide concentrations. This is a boon for the plant, allowing for more efficient photosynthesis, the chemical process by which plants make food for themselves, which requires both carbon dioxide and water.

Better photosynthesis helps plants grow bigger — which in turn allows them to store more carbon away. That means if plants around the world continue to adjust to rising carbon dioxide concentrations, increasing their biomass on a global scale, they could actually help offset some of our human carbon emissions by removing more carbon dioxide from the air.

“There’s more photosynthesis going on than in the past, and there’s more biomass,” said the new study’s lead author, Ralph Keeling, a professor of geochemistry at the Scripps Institution of Oceanography and program director of the Scripps CO2 Program. “And the accumulation of biomass is important, because it’s carbon that otherwise would have been in the air that got taken out and is slowing down the growth rate of atmospheric carbon dioxide. These things all hang together.”

In fact, the researchers suggest not only that changes in global plant behavior may actually be enough to alter the composition of carbon atoms in the atmosphere, but that this process can help solve a puzzling mystery about what’s happening to all the carbon dioxide we put into the atmosphere.

Carbon atoms can come in several different forms, called “isotopes.” The most common is carbon-12, which has six protons and six neutrons and accounts for about 99 percent of all naturally occurring carbon on Earth. Another isotope is carbon-13, a slightly heavier atom with six protons and seven neutrons, accounting for the other 1 percent.

It turns out that most plants tend to favor carbon-12 over carbon-13 for carrying out the chemical processes involved in photosynthesis. This means plants tend to contain an even smaller ratio of carbon-13 to carbon-12 than naturally occurs in the atmosphere.

Because fossil fuels, such as oil, are naturally formed from dead plant matter, they also contain a smaller ratio of carbon-13 to carbon-12. Burning them releases this plant-derived carbon — rich in carbon-12 and deficient in carbon-13 — into the air all at once, changing the naturally occurring ratio of carbon isotopes found there.