As the Earth's climate continues to warm, the elevated temperatures can put a strain on agriculture. Although an increase in the average temperature can harm crops, it's the details obscured by that average that can cause the biggest problems: more—and more extended—periods of extreme temperatures often harm crops far more than raising the typical temperature a fraction of a degree.

Fortunately, as a team of Swiss and French researchers have determined, the opposite may also be true. They've identified a simple agricultural practice that does little to alter the average temperature of farming areas. But it does have a strong effect on extreme temperatures, lowering them by nearly 2°C. That should be enough to keep existing crops viable for longer in the face of future climate change.

The technique in question is called "no-till farming," and it simply involves leaving the debris from previous crops on the surface of the fields rather than plowing the fields and exposing the soil underneath. Observations of test agricultural fields indicate that no-till practices have several effects. To begin with, the debris tends to retain moisture, which limits evaporation; since evaporation cools the surface, this tends to have a warming effect. But this warming is extremely limited on the hottest days, when the intense heat drives evaporation even when plant debris is present.

The agricultural debris also has an effect on albedo, the amount of sunlight that gets reflected back from the Earth's surface. After a rain storm, the tillage was about as dark as the soil underneath it. But on drier days, the plant material reflected significantly more sunlight than the soil. This effect was amplified further on the hottest days, which are typically cloud-free, which allows the reflected sunlight to escape into space.

To figure out how all of this added up, the authors used a regional climate model and explored how no-till farming would alter the temperatures of European agricultural areas. For most conditions, it made very little difference. But on the warmest days, the models of no-till fields had temperatures that were 2°C lower than if the same fields were plowed. A similar result was obtained when the authors used the model to recreate a 2003 heat wave that baked France and warmed the rest of Europe.

Currently, no-till farming is largely practiced in the Americas and rarely used in Europe. Adopting it can require the purchase of new equipment and adoption of different techniques. But these results suggest that no-till agriculture can also protect crops when they're at their most vulnerable: during periods of extreme heat.

PNAS, 2014. DOI: 10.1073/pnas.1317323111. (About DOIs).