It's that time again: time to take a hike and enjoy the splendid fall foliage. Or, if you live in a tourist town like I do, time to see "leaf peepers" driving their cars aimlessly throughout the countryside searching for a stand of incredibly red maples or golden oaks. If climate change continues on its present course, however, you might want to mark future calendars a bit later than usual for the best day to take that walk or ride. Trees use a combination of cues to determine when to drop their leaves, but the two primary signals are the length of daylight, and temperature. Sunlight is the major factor; as trees sense fewer hours of light, they curtail photosynthesis in their leaves. Green chlorophyll fades, and colors emerge. Climate change has no effect on day length, but it does on temperature. If autumn days are warm, trees tend to delay the color change, and if autumn days are cool, they tend to hasten the pace. If global temperatures generally rise, you may need to take that walk a few days later. Indeed, Massachusetts officials have determined that the average peak color change has shifted about three days later over recent decades. Climate change could also alter precipitation, which can affect colors as well. The amount of rainfall does not seem to be a factor, but more cloudy days lowers the level of daylight, which tends to lessen the intensity of a leaf's color. For more details, check out this video, produced by our partners at Accuweather.com. And if you're driving through my town this fall, wave hello, but keep your eyes on the trees (I mean, the road).