Volcanic and solar impacts on climate since 1700

Numerical experiments have been carried out with a two-dimensional sector averaged global climate model with a detailed radiative scheme in order to assess the possible impact of solar and volcanic activities on the Earth's surface temperature at the secular time scale from 1700 to 1992. Our results indicate that while the general trend of the observed temperature variations on the century time scale can be generated in response to both the solar and volcanic forcings, these are clearly not sufficient to explain the observed 20th century warming and more specifically the warming trend which started at the beginning of the 1970s. However, the lack of volcanism during the period 1925-1960 could account, at least partly, for the observed warming trend in this period. Finally, while Schlesinger and Ramankutty (1994) assumed that random forcing could not be a possible source of the 65-70 year oscillation they detected in the global climate system, our results indicate that the volcanic forcing over the past 150 years could have introduced an oscillation of around 70 years in the Earth's surface temperature.