Understanding the role of clouds and cloud processes in the earth's climate system.

Evidence now firmly establishes that our species is altering the global climate through the combustion of fuels that warm the earth's atmosphere. The climate of the Earth is a highly complex and nonlinear system that does not necessarily respond in a simple or even predictable way. For instance, computer model simulations suggest that an increase in certain clouds in the upper troposphere could enhance global warming while an increase in certain cloud types in the lower troposphere could offset the warming. Currently, the leading climate models differ substantially in their predicted global warming and even more significantly, they differ widely in the predicted regional changes. Several leading scientific organizations including the World Meteorological Organization and the Intergovernmental Panel on Climate Change have identified the influences of clouds as the leading cause of this uncertainty. We are currently quite active in this research arena.

The U.S. Department of Energy through the Atmospheric Radiation Measurement (ARM) program, designed to improve the characterization of clouds in climate models. The program has established several heavily instrumented research sites in climatically significant locales. A site was established in the early 1990's in north central Oklahoma, and sites in the tropical western Pacific and on the North Slope of Alaska have been collecting data since 1998. All The ARM sites use state of the art remote sensors such as millimeter and laser radar to probe clouds that occur over the sites. Our task is to examine this continuous data stream, identify when clouds occur and deliver quantitative analyses of the cloud properties and their effect on the solar and terrestrial radiation streams.

NASA has also taken a leading role in examining the Earth's changing climate. In April, 2006, The satellites known as Cloudsat and Calipso were launched into orbit and are now flying close formation with a constellation of other satellites. This satellite constellation, known as the A-Train, has initiated a new era of earth observations. We look forward to contributing to this exploration of our home planet in the coming years.