Cosmic rays are high speed sub-atomic particles from outer space, mostly from our Milky Way galaxy, and affect cloud formation, which in turn affect climate.
Clouds are formed by the condensation of supersaturated water vapor in the atmosphere into water droplets. Water is introduced to the atmosphere mainly form the oceans, predominantly the tropics (warmer water). As water vapor rises in the atmosphere and cools, it often becomes supersaturated: its vapor pressure is above that necessary for condensation.
The mechanism of condensation is complex, but one thing known to promote condensation, and thus cloud formation, is high speed sub-atomic particles. This was observed and used as an early technique of studying nuclear reactions – the Wilson Cloud Chamber, depicted below:
The short, thick traces (mini-clouds) are alpha particles (helium nuclei). The thin traces are beta particles (electrons).
The figure below represents the cosmic ray – cloud correlation in recent times.
Effect of Sunspots on Cosmic Rays.
Our sun has a magnetic field strong enough to affect nature on earth. Our sun also emits protons and electrons to space at a somewhat constant rate, known as the Solar Wind, which also effects the earth. One visible effect of the solar wind is the Aurora Borealis. The Van Allen Belt consists of solar wind and cosmic rays entrapped by earth’s magnetic field. Occasionally there are storms on the surface of the sun, called sun spots, that create surges in the magnetic field and solar wind. Sunspots are cyclical, in an approximate 11 year period. Sunspots have been found to affect cosmic rays striking earth, which also affects cloud formation.
Effect of Cosmic Rays on Earth’s Surface Temperature
The figure below is a correlation over the phanerozoic period (525 million years) between cosmic rays and global temperature. Source: Adapted from N.J. Shaviv, and J. Veizer, 2003. “Celestial Driver of Phanerozoic Climate?” GSA Today (July), pp. 4-10
Temperature & Cosmic Rays, Millions of Years from Present
The “Phanerozoic Period” begins with the appearance of animal (zoological) life up to the present.