The Cloud Mystery | Henrik Svensmark

Nir Shaviv and Henrik Svensmark (HERE)

Looking at the Milky Way from above, we see four giant spiral arms. Our solar system is currently located within a small armlet called Orion between the two big spiral arms Sagittarius-Carina and Perseus. But it doesn’t stay there. It rotates at a speed of some 830,000 kilometers per hour around the galactic center and does a whole round about every 250 millions years. This rotation period is called one galactic year. That means on average every about 65 million years our solar system moves through one of the major spiral arms of the milky-way. 

The Solar System's passage
through the Milky Way (HERE)

During such a passage the average temperature on Earth is about 5-10°C colder than outside the spiral arms where more clouds can be created and are causing cooler climatic conditions. Within a spiral arm more cosmic rays reach the Earth because there are more super novae in the immediate neighborhood of our solar system. These dying stars are sending out cosmic rays, subatomic particles with enormous energy rushing through the galaxy at almost the speed of light. And some of them shower and bombard the Earth. In our atmosphere the cosmic rays are nuclei for condensation of water vapor and cloud formation. And the clouds reflect the sunlight and cool the Earth.

The Sun of course also plays an important role in the formation of clouds: When there are a lot of sunspots, the magnetic fields of the Sun are emitting more charged particles, called the solar wind. The solar wind fights and neutralizes the cosmic rays and controls how many of them reach the Earth. During the 20th century the magnetic activity of the Sun has almost doubled. As a result fewer cosmic rays reach the Earth, the cloud cover became thinner and the Earth’s climate warmer. 

Nir Shaviv (HERE)

A ‘lazy’ Sun would produce less magnetic activity, less solar wind and more cosmic rays would reach the Earth’s atmosphere able to build up clouds there and to cool the planet’s climate down: The Sun controls the Earth’s cloudiness. The climate is controlled by the clouds. The clouds are controlled by cosmic rays. And the cosmic rays are controlled by the Sun.

Sources: Henrik Svensmark and Eigil Friis-Christensen, astrophysicists, Danish National Space Institute (DTU Space), Copenhagen | Nir Shaviv, astronomer,  Racah Institute of Physics, Hebrew University of Jerusalem | Jan Veizer, geologist, Department of  Earth Sciences, University of Ottawa and Institute for Geology, Mineralogy and Geophysics, Bochum Ruhr University | Jasper Kirkby (2011): The CLOUD experiment at CERN [65 m] | Lars Oxfeld Mortensen (2007): The Cloud Mystery - Henrik Svensmark on Climate Change [53 m] | Martin Durkin (2007): The Great Global Warming Swindle [76 m]