The link between cosmic rays and cloud formation ~ Center for Sun-Climate Research

For more than 20 years, satellite records of low-altitude clouds have closely followed variations in cosmic rays (diagram 1). Just how cosmic rays take part in cloud-making appeared in the SKY experiment, conducted in the basement of the National Space Institute. Electrons set free in the air by passing cosmic rays help to assemble the building blocks for cloud condensation nuclei on which water vapour condenses to make clouds

Cosmic-ray Intensities and Low-level Cloud Formation
1. Red depicts cosmic-ray intensities and blue, the low-level cloudiness

via Center for Sun-Climate Research.

Comment:~ It is important to bear in mind that the researchers do not exclude man-made warming, but treat this as one of several factors that influence climate change:

“The significant contribution from solar activity variations to global temperature increase does not, however, exclude other contributions to the rising global temperature, natural as well as human. However, taking into account the large uncertainty associated with the estimated human contribution, a good research-based estimate of the range of natural climate variations is an essential information. The NSI is focused on establishing the best possible and scientifically based evaluation of the size of solar induced effects on climate.”

Climate change during the Earth’s history ~ Center for Sun-Climate Research

On long timescales the intensity of cosmic rays varies more emphatically because the influx from the Galaxy changes. During the past 500 million years, the Earth has passed through four ‘hothouse’ episodes, free of ice and with high sea levels, and four ‘icehouse’ episodes like the one we live in now, with ice-sheets, glaciers and relatively low sea levels.

Nir Shaviv of the Hebrew University in Jerusalem, together with Ján Veizer of the Ruhr University and the University of Ottawa, links these changes to the journey of the Sun and the Earth through the Milky Way Galaxy. They blame the icehouse episodes on encounters with bright spiral arms, where cosmic rays are most intense (diagram 3).

Changes in Tropical Sea-surface Temperatures over the past 500 million years Compared to Cosmic-rays Intensities

3. The red curve shows changes in tropical sea-surface temperatures over the past 500 million years. In the blue curve, drawn upside down to match, cosmic-rays intensities have varied according to our position relative to the Galaxy’s spiral arms. After Shaviv and Veizer

More frequent chilling events, every 34 million years or so, occur whenever the solar system passes through with the mid-plane of the Galaxy.

via Center for Sun-Climate Research.

Comment:~ What does not appear to be adequately explained is the divergence between tropical sea-surface temperatures and cosmic ray intensities in the latest cycle.