SAVOY, Ill. — From afar, the three young men tramping through a corn field here looked like Midwestern farm boys checking their crop. And a fine crop it seemed to be, with plump ears hanging off vibrant green stalks.

But as they edged deeper into the field, the men — actually young scientists, not farmers — pointed to streaked, yellowing leaves on some of the corn plants. “You’re definitely seeing some damage,” said Tiago Tomaz, a biochemist from Australia.

The injured leaves signaled trouble down the road, and not just for a single plot of corn a few miles from the main campus of the University of Illinois. By design, the scientists were studying the type of damage that could put a serious dent in the food supply on a warming planet.

The fields here are among a handful of places in the world where researchers are trying to mimic the growing conditions expected to arise decades in the future as the air fills with heat-trapping gases and other pollutants from human activity.