A cloud is a visible mass of water droplets or frozen ice crystals suspended in the Earth’s atmosphere above the surface of the Earth or other planetary body. On a cloudy day the surface under the clouds appears darker and cooler. Atmospheric scientists trying to pin down how clouds curb the amount of sunlight available to warm the earth have found that it depends on the wavelength of sunlight being measured. This unexpected result will help researchers improve how they portray clouds in climate models. Additionally, the researchers found that sunlight scattered by clouds — the reason why beach goers can get sunburned on overcast days — is an important component of cloud contributions to the earth’s energy balance. Capturing such contributions will increase the accuracy of climate models, the team from the Department of Energy’s Pacific Northwest National Laboratory reported in Geophysical Research Letters earlier this month.