A review of the relevance of the 'CLOUD' results and other recent observations to the possible effect of cosmic rays on the terrestrial climate

TL;DR

This review assesses recent experimental and observational evidence on cosmic rays' influence on climate, concluding that current data do not support a significant impact on atmospheric cloud formation or global warming.

Contribution

It critically evaluates recent CLOUD project results and stratospheric aerosol studies, clarifying their implications for cosmic rays' role in climate change.

Findings

CLOUD results do not support significant cosmic ray influence on clouds

Stratospheric aerosol changes post-solar events are negligible

Cosmic ray variations suggest a small cooling effect, not warming

Abstract

The problem of the contribution of cosmic rays to climate change is a continuing one and one of importance. In principle, at least, the recent results from the CLOUD project at CERN provide information about the role of ionizing particles in 'sensitizing' atmospheric aerosols which might, later, give rise to cloud droplets. Our analysis shows that, although important in cloud physics the results do not lead to the conclusion that cosmic rays affect atmospheric clouds significantly, at least if H2SO4 is the dominant source of aerosols in the atmosphere. An analysis of the very recent studies of stratospheric aerosol changes following a giant solar energetic particles event shows a similar negligible effect. Recent measurements of the cosmic ray intensity show that a former decrease with time has been reversed. Thus, even if cosmic rays enhanced cloud production, there will be a small global cooling, not warming.