Total Solar Irradiance Trends During Solar Cycles 21-24

Total solar irradiance (TSI) observations have been made by contiguous, redundant, overlapping satellite experiments since 1978 during solar activity cycles 21 - 23. The solar activity minimum marking the inception of cycle 24 is imminent - some sunspot magnetic polarity reversals have already been detected. The ACRIM TSI composite time series found a 0.04 percent per decade trend between the minima of cycles 21 to 23. A trend of this magnitude, sustained over many decades or centuries, could be a significant climate forcing. Great interest will be attached to the behavior of the TSI time series during the upcoming and future solar activity minima with respect to the presence or absence of a trend. An updated TSI composite will be presented to examine the trend at or near the minima between solar cycles 23 and 24.