VARIATIONS OF TOTAL SOLAR IRRADIANCE AND THEIR IMPLICATIONS FOR CLIMATE CHANGE

Contiguous Total solar irradiance (TSI) observations have been made by overlapping satellite experiments since 1978 during solar activity cycles 21 - 23. A TSI composite time series constructed from these results demonstrates a 0.04 percent per decade upward trend between the minima during cycles 21 to 23. As the next solar minimum approaches it appears the trend will be smaller between solar cycles 21 and 24. Yet even a smaller trend, sustained over climate time scales, could be a significant climate forcing. While the sensitivity of climate change to TSI variation has yet to be established quantitatively, recent phenomenological modeling has shown that TSI variation could have provided a significant component of the climate change during the industrial era and was the driving force behind the medeival climate optimum and the ensuing little ice age.