by Gordon Fulks
I finally had a chance to watch the movie about Svensmark’s work on “The Cloud Mystery” and found it fascinating. Both Svensmark from Denmark and Nir Shaviv from Hebrew University in Israel make a strong case for a galactic cosmic ray origin for climate change over periods as short as a decade to as long as 150 million years:
The short term variations in the galactic cosmic rays and therefore the cloud cover are caused by variations in the solar magnetic field frozen into the solar wind. This large spiral magnetic field is carried out to about 100 AU in roughly a year by the supersonic solar wind traveling at 400 km/sec. It modulates incoming galactic cosmic rays by convecting them out of the solar system as they attempt to diffuse inward. Sunspots are the visual manifestation of the Sun’s magnetic activity. We have records of them going back to Galileo in 1610.
Very long term variations in the cosmic rays reaching the earth are caused by the solar system’s orbit about the center of our Milky Way galaxy. When we enter one of the major spiral arms of the galaxy, the galactic cosmic ray intensity increases which increases our cloud cover and cools the earth. The data show periodic cooling of the earth over periods of 150 million years corresponding to entry into the spiral arms. (more…)