A comparison of variable solar total and ultraviolet irradiance outputs in the 20th century

[1] Differences in time-variation between total and ultraviolet solar irradiance could help in separating their influence on climate. We present the first models based on area measurements of magnetic plages from CaK spectroheliograms obtained between 1915-1999. Correlation of our time series of UV irradiance with global temperature, T, accounts for only 20% of the global temperature variance during the 20th century. Correlation of our total irradiance time series with T accounts statistically for 80% of the variance in global temperature over that period, although the irradiance variation amplitude is insufficient to influence global warming in present-day climate models. This interesting difference has been obscured in past modelling by additional components introduced to represent secular variations, which are no longer supported by current observational evidence. Future irradiance models emphasizing the more securely-based contributions of photospheric magnetic structures seem to provide better prospects for improved physical understanding of sun-climate links.