The 10th Symposium on Global Change Studies

3B.20
THE ROLE OF SOLAR AND VOLCANIC FORCING IN THE LITTLE ICE AGE

Melissa P. Free, Univ. of Maryland, College Park, MD; and A. Robock

The possible causes of climate change for the last 600 years include solar and volcanic forcings, anthropogenic factors, and internal variability of the climate system, with anthropogenic factors probably important only for the past 150 years at most. To evaluate the significance of solar and volcanic effects, we use four solar reconstructions and three volcanic indices as forcings to an energy-balance model and compare the results to several temperature reconstructions from 1400 to the present. The model outputs show important differences from the equilibrium responses to the forcings, particularly for the solar reconstructions. Our results show some statistically significant relationships between solar- and volcanically- forced model results and the temperature record, varying substantially depending on choice of forcing, temperature series and time period. While the correlations suggest similar roles for both volcanic and solar forcing, only the volcanically forced outputs produce responses equal in size to the cooling of the Little Ice Age. Using a middle-of-the-road model sensitivity of 3 degrees C for doubled CO2, solar output changes of less than 0.5% are too small to account for the cooling of the Little Ice Age. A combination of solar and volcanic forcings explains much of the Little Ice Age climate change, but these factors alone cannot explain the warming of the 20th century. The best simulations of the period since 1850 include anthropogenic, solar and volcanic forcings

The 10th Symposium on Global Change Studies