Weeds, those unwanted, unloved and annoying invasive plants that farmers and gardeners hate amid their plantings, are expanding to northern latitudes, thanks to rising temperatures.

"Weeds are the wild relatives of many of our crops," says Antonio DiTommaso, a weed ecologist and Cornell associate professor in the Department of Crop and Soil Sciences. "Weeds will be the harbingers of global warming. They'll tell us what kind of species of crops will likely survive in a changing climate."