Testing the proposed link between cosmic rays and cloud cover

TL;DR

This study critically examines the proposed link between cosmic ray variations and changes in global cloud cover, finding no supporting evidence and estimating a minimal contribution to observed cloud cover changes.

Contribution

The paper provides a rigorous analysis that challenges the hypothesis of cosmic rays significantly influencing cloud cover, offering a quantitative estimate of their limited impact.

Findings

No evidence supporting the cosmic ray-cloud cover link was found.

Less than 23% of the observed cloud cover change is attributable to cosmic ray variations.

The hypothesis that cosmic rays drive significant cloud cover changes during solar cycles is doubtful.

Abstract

A decrease in the globally averaged low level cloud cover, deduced from the ISCCP infra red data, as the cosmic ray intensity decreased during the solar cycle 22 was observed by two groups. The groups went on to hypothesise that the decrease in ionization due to cosmic rays causes the decrease in cloud cover, thereby explaining a large part of the presently observed global warming. We have examined this hypothesis to look for evidence to corroborate it. None has been found and so our conclusions are to doubt it. From the absence of corroborative evidence, we estimate that less than 23%, at the 95% confidence level, of the 11-year cycle change in the globally averaged cloud cover observed in solar cycle 22 is due to the change in the rate of ionization from the solar modulation of cosmic rays.