If you’ve ever made the mistake of wearing a black shirt on a sweltering day, you know that dark colors absorb the sun’s heat, while light colors reflect it. Our planet works the same way. White surfaces, like the snow on the world’s glaciers, reflect the sun’s rays back toward space. Darker ones, like forests and oceans, absorb more heat. Overall, about 30 percent of the energy sent to Earth bounces back into outer space, stabilizing the global thermostat. But climate change could upend that balance.