The world’s hottest rainforest is located not in the Amazon or anywhere else you might expect, but inside Biosphere 2, the experimental scientific research facility in the desert outside Tucson, Arizona. A recent study of tropical trees planted there in the early 1990s reported a surprising result: They have withstood temperatures higher than any likely to be experienced by tropical forests this century.

The study adds to a growing tally of findings that are giving forest scientists something that’s been in short supply lately: hope. Plants may have unexpected resources that could help them survive—and perhaps even thrive—in a hotter, more carbon-rich future. And while tropical forests still face both human and natural threats, some researchers believe dire reports of