Active Cavity Radiometer Irradiance Monitor (ACRIM)

The Active Cavity Radiometer Irradiance Monitor (ACRIM) I instrument was the first to clearly demonstrate that the total radiant energy from the sun was not a constant. However, the solar variability was so slight (0.1% of full scale) that continuous monitoring by state-of-the-art instrumentation was necessary. It is theorized that as much as 25% of the anticipated global warming of the earth may be solar in origin. In addition, seemingly small (0.5%) changes in the TSI output of the sun over a century or more may cause significant climatological changes on earth.

STS-41C