Utah, Ohio, and Canada might soon be dotted with palm trees—because welcome to climate change. Following a 2007 study that found palm trees in the foothills of the Swiss Alps, an international team of researchers set out to learn how cold is too cold for palm trees. Upon surveying global data, they determined most palm species (there are 2,500) grow successfully in the wild if a region's coldest month is above 41.36 degrees Fahrenheit on average, per Atlas Obscura. A handful of cold-tolerant palms, like the windmill palm, however, can grow in areas with a coldest month temperature above 36 degrees on average. With an average temp of 34 degrees in January, Washington, DC, isn't quite there, researchers say, but they note it could warm enough "in the coming decades" to allow palms to flourish, reports Weather.com.
The same goes for the Northeast, Northwest, parts of Canada, and other parts of the world that have long been too cold for palms. "In all of these areas palms in people's gardens are flowering and setting fruit," study co-author David Greenwood says, per Earther. But "just because you can grow a windmill palm or another cold-tolerant palm in your yard in Utah, British Columbia, or Ohio, doesn't mean that species can colonize the nearby woods." For that to happen, seedlings—which are less tolerant of the cold than adult plants—must be able to survive their first winter, and that will take "a little bit more warming," Greenwood says. The study in Scientific Reports also looked at palms in the fossil record, noting their presence suggests a minimum temperature of roughly 36 degrees. (Los Angeles is losing its palm trees.)