NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

Support for this project was provided by the National Oceanic and Atmospheric Administration under Contract No. NASW-01008. Any opinions, findings, and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.

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Cover: Images obtained from the Clouds and Earth’s Radiant Energy System (CERES) instrument on board NASA’s Aqua satellite on June 22, 2002. The image on the front cover shows the amount of infrared energy, or heat, emitted by the Earth and its atmosphere to space. Clear, warm land regions (shown in yellow) emit the most heat. High, cold clouds (shown in blue and white) emit less heat to space. The image on the back cover shows the amount of sunlight reflected back to space. Clear ocean areas (shown in dark blue) reflect the least amount of sunlight back to space, and clouds and snow-covered surfaces (shown in white and green) reflect the most sunlight back to space. SOURCE: National Aeronautics and Space Administration (NASA) Goddard Space Flight Center.