Credit: NASA Earth Observatory
Infrared image from the GOES satellite captured on May 30, 2010. White and light grey correspond to emissions from warm surfaces and warm, low clouds; black or dark is from high, and consequently cold, clouds. Low clouds, like oceans and land, send more infrared radiation back out into space than high, cold clouds. Because low clouds also reflect visible light, they have a net cooling effect; by contrast high clouds do not block incoming sunlight much but do inhibit the outflow of infrared radiation and hence warm the planet.