Why rising carbon dioxide may actually help some crops

Researchers reveal another effect of climate change and rising carbon dioxide levels: better growth potential and drought resistance for some crops. 

Scientists have long expressed concerns that global climate change could negatively impact agriculture, but a new study published this week in the journal Nature Climate Change shows that rising levels of carbon dioxide in the Earth's atmosphere could actually aid plant growth in some regions.

When scientists share concerns about climate change hurting crops, they generally talk about water scarcity and high temperatures. This latest study, conducted by an international team of 16 researchers, finds that rising carbon dioxide levels that accompany and exacerbate climate change can also enhance photosynthesis and reduce plants' need for water.

"Most of the discussion around climate impacts focuses only on changes in temperature and precipitation," said lead author Delphine Deryng, an environmental scientist at Columbia University's Center for Climate Systems Research in New York, in a press release. "To adapt adequately, we need to understand all the factors involved."

The study used climate data and carbon dioxide experiments in fields to study the impact of climate change and rising carbon dioxide levels on crops.

Carbon dioxide (CO2) levels have risen by a quarter since 1980, according to scientists, and they are predicted to continue to rise along with global temperatures.

In the study, scientists estimated growth rates of four different kinds of crops: wheat, rice, maize, and soybeans. They created two simulations: one in a world with rising CO2 levels and climate change, and the other in a world with CO2 emissions at today's rate, but with continuing climate change.

The scenario with rising temperatures, but no rise in carbon dioxide in the atmosphere, saw severe negative impacts on crop yields by the end of the century. In the scenario with both rising temperatures and rising carbon dioxide, crop yields either remained the same or losses were mitigated by the rise in CO2.

Why?

Rising carbon dioxide levels can improve water-use efficiency, the researchers found. Wheat is predicted to use water 27 percent more efficiently by 2080. Efficiency is predicted to grow by 10 percent in rice crops.

On the other hand, crop yields are predicted to go down – wheat by 4 percent and maize by more than 8 percent. Deryng also added that not much is known about the impact of changing CO2 levels on crop nutrition.

The study paints a complicated picture of an already complicated issue. While carbon dioxide can help plants, climate change can present other problems that hurt them, including weather events like heat waves.

Retired US Department of Agriculture researcher Bruce Kimball praised the paper's overall accuracy, though he said that more data is needed. Deryng concurred, saying that researchers had not been able to conduct field experiments in Africa, South America, or India.

Dr. Kimball also said that after a certain point, the benefits of a greater CO2 concentration in the atmosphere are negated by ever warmer temperatures.

"Thus, for greater warming and higher CO2," said Kimball in a Columbia University press release, "the results would likely be more pessimistic than shown in this paper."

Deryng agrees that the study's findings should not be interpreted as a universally good thing.

"We need to take into account all of the processes involved, including the negative effects, including increases in temperatures and increases in heat waves, but there is also this process that will happen with more CO2," says Deryng in a phone interview with The Christian Science Monitor. "This effect will not fully counterbalance the negative effects of climate change, but it will help us prepare."