Climate from Earthshine
May 01, 2001
Earthshine (sunlight reflected from the Earth) illuminates the dark face of the Moon in this long exposure made by Chris Proctor of the Torbay Astronomical Society. As a result, the sunlit crescent on the left is greatly overexposed. The ghostly glow from the shadowed side of the moon can be measured very carefully to determine how bright the Earth is - a brighter Earth means more reflected sunlight and implies a cooler Earth overall. Long-term observations of earthshine thus monitor variations in cloud cover and atmospheric particles known as aerosols that play a role in climate change. A team of scientists from Caltech and the New Jersey Institute of Technology has found surprisingly large--up to 20 percent--seasonal variations in Earth's reflectance. Further, their measurements hint at a 2.5-percent decrease in Earth's albedo over the past five years, indicative of a dimmer, warmer Earth. During the same period the Sun's magnetic activity has climbed from solar minimum to maximum, supporting the hypothesis that the Sun's magnetic field plays an indirect role in Earth's climate.