New

satellite mission providing global cloud and aerosol profiles David Winker CALIPSO, one of NASA’s newest satellite missions, is providing ob-servations of cloud and aerosol to improve our understanding of their role in Earth’s climate system. Climate models show that increasing levels of CO2 and other greenhouse gases are driving changes in Earth’s climate. But aerosols and clouds affect the flow of solar and thermal radi-ation in the atmosphere, and thus modify the warming effect of greenhouse gases. Atmospheric aerosols, such as desert dust and smoke, both reflect and absorb sunlight, cooling the Earth’s surface. Clouds reflect sunlight, which has a cooling effect, but also trap outgoing thermal radiation, which has a warming effect. The balance between these two opposing cloud effects depends, among other things, on the altitude of the clouds. Much of the current uncertainty about the effects of aerosols and clouds on Earth’s climate is due to our limited ability to globally monitor aerosols and clouds from satellites. Aerosols over bright surfaces, such as deserts, are difficult to see from space, and the lifetimes and radiative effects of aerosols depend on their altitude. Clouds often occur in multiple layers, which strongly influences their radiative effects. Lidar can overcome these observational difficulties. It can provide vertical profiles of aerosols and multi-layer cloud structures, and can observe thin cloud and aerosol layers that passive instruments cannot detect