Heat waves hurt corn more than CO2 helps

Source: Tiffany Stecker, E&E reporter • Posted: Friday, March 21, 2014

Corn yield losses could be twice as severe if heat waves occur during a crop’s flowering period, despite the benefits that a richer CO2-laden atmosphere might offer plants.
Farmers have long known that unusually hot days can devastate crops if they fall during anthesis, the flowering phase that is critical for reproduction. Extreme heat during anthesis can make a plant sterile. Now, a group of crop and climate scientists have predicted exactly how much these events can cut global yields of corn, soybeans and wheat. While some crops are expected to benefit from more carbon dioxide in the future, heat stress will likely erode that boost.”What we find here is the positive effect is largely offset by heat stress,” said Delphine Deryng, a Ph.D. student at the Tyndall Centre for Climate Change Research at the University of East Anglia in the United Kingdom.But two other major crops — soybeans and winter wheat — would see less damage from high temperatures during anthesis. This is because these crops could benefit more from high concentrations of CO2 in the atmosphere, which nourishes plants through photosynthesis and allows crops to be more productive.

Researchers at the Tyndall Centre, the Grantham Research Institute at the London School of Economics and McGill University in Montreal set up crop models, accounting for both anthesis and carbon dioxide fertilization between the 1980s and the 2080s. There were eight scenarios: four accounting for different degrees of climate change, two that didn’t incorporate heat waves during anthesis and two that didn’t count the CO2 fertilization effect. The scientists published theirfindings yesterday in Environmental Research Letters.

Some studies have examined the effect of extreme heat on anthesis on the regional scale, but this is the first time researchers have looked at the effect on a global scale, Deryng said.

Although wheat and soybeans are projected to experience less damage than corn, they will still have smaller yields despite higher amounts of CO2. Heat during anthesis would reduce CO2-enhanced gains by half for wheat and by a quarter for soybeans.

Smaller yields expected

Crop losses also vary according to their location in the world. Sub-Saharan Africa and Latin America are likely to see at least 50 percent reductions for corn, given the heat waves during anthesis. However, without the heat effect on flowering, the Southern Hemisphere’s corn yields would remain relatively unchanged, or grow a little.

The anthesis effect led to dramatic changes in certain countries. Inland Peru’s wheat fields could see a 50 percent increase with the extra CO2, but if heat waves disrupt the flowering, the country is likely to see losses, according to one of the study’s figures.

The anthesis effect is less pronounced in northern Europe, Russia and China, where carbon fertilization will help.

So why does corn lose out on the benefits of carbon dioxide? It’s designated as a C4 plant, Deryng said. This means it’s naturally very efficient at processing CO2, whereas C3 crops like wheat and soybeans are less so and have more to gain from the fertilization effect.

This experiment is an example of a “gridded” crop model, which overlaps crop models from field trials, data sets and computing power to create a grid over the world that shows crop yield trends in different scenarios.

This is one of the first studies to assess a specific climate vulnerability in a crop, said Alexander Ruane, science coordinator for the Agricultural Model Intercomparison and Improvement Project and a research physical scientist at the NASA Goddard Institute for Space Studies.

“This specific focus on how extreme events interact with climate change to affect crops is an important next step for us in addressing food security challenges,” he said.

Last week, a study in Nature Climate Change found that wheat, corn and rice yields will greatly decline by the second half of this century (ClimateWire, March 19).