Are cosmic rays influencing oceanic cloud coverage - Or is it only El Nino?

Abstract

The monthly average (C2) cloud coverage data produced by the International Satellite Cloud Climatology Project (ISCCP) for the period of July 1986-June 1991 show strong global and regional cloud coverage variations associated with the El Nino of 1986-1987. The Pacific Ocean, in particular, shows strong regional variations in cloud coverage. These agree well with contemporaneous satellite observations of broadband shortwave infrared cloud forcing measured by the Earth Radiation Budget Experiment. Svensmark and Friis-Christensen (1997) noted a similarity between the shape of the time series curve of average cloud coverage fraction for mid- to low-latitude ocean-areas and the time series curve of cosmic ray flux intensity. They proposed a causal relationship - A 'missing link' for solar cycle influence on Earth climate. Further spatial and temporal analysis of the same ISCCP C2 data in this paper indicates that the cloud coverage variation patterns are those to be expected for the atmospheric circulation changes characteristic of El Nino, weakening the case for cosmic rays as a climatic forcing factor.