Constraints on Long-Term Variability of the Solar Luminosity

Steven Spangler; Professor emeritus of physics and astronomy, University of Iowa

Observed global warming over the last 50–100 years is reliably attributed to the substantial increase in atmospheric carbon dioxide over the same period. However, an increase in the solar luminosity of 1.5% could cause the same change of about 1K in the global average temperature. No such change has occurred in the solar luminosity over the past 50 years, but we do not know if the sun has shown greater variability over timescales of millenia or more. Such variations could account for past climate changes that clearly were not due to anthropogenic carbon dioxide. In this talk, I will review previous work to measure or constrain variations in the solar luminosity over times scales of centuries to thousands of years. My own activity consists of measuring or limiting the dispersion of luminosities of solar-type stars in the star cluster Messier 67.