Launched Dec. 20, 1999, the Active Cavity Radiometer Irradiance Monitor Satellite (AcrimSat) monitors the total amount of the sun's energy reaching Earth.

It is this energy, called total solar irradiance, that creates the winds, heats the land and drives ocean currents.

Some scientists theorize a significant fraction of Earth's warming may be solar in origin due to small increases in the sun's total energy output since the last century.

By measuring incoming solar radiation, climatologists are using AcrimSat to improve their predictions of climate change and global warming over the next century.