Friday, 2 September 2011

Cosmic weather and climate change

A previous post showed the complex range of interacting factors which climate change models have to take into account. One of these was clouds. Depending on the type, amount, thickness and height these can have marked cooling or warming effects on the atmosphere.

The water vapour in the air is a dry colourless gas until it encounters ‘condensation nuclei’, microscopic particles floating in the air which cause condensation of water vapour into its liquid form in the same way that steam forms in bathrooms. Steam, fog and cloud are not water vapour – they consist of microscopic droplets of water which grow when the dry vapour comes into contact with the condensation nuclei.

One source of condensation nuclei now appears to be cosmic rays. Recently  CERN, an elementary particle physics lab near Geneva, has precisely simulated the composition of the Earth’s atmosphere (CLOUD, cosmics leaving outdoor droplets). The condensation nuclei created in the simulated atmosphere form about 10 times more readily when bombarded with simulated cosmic rays than when left unbombarded. So it appears that cosmic rays, mainly protons from supernovae (exploding stars) within our galaxy, typically thousands of light years away, play an important role in forming condensation nuclei and this must have a significant effect on cloud formation. 

But the cosmic rays from the depths of space do not hit the Earth’s atmosphere regularly over time. They are modulated by the solar wind and its associated interplanetary magnetic field, much weaker than our own magnetic field which offers a strong protective shield known as the Van Allen Belts. (Without these Belts life is unlikely to have evolved.)

The solar wind varies with the sunspot cycle, 11 years on average. The more active the sun the more we are protected from the cosmic rays, so the fewer will be the condensation nuclei, which means less cloud formation, which in turn means ....? No-one is sure because we don’t understand enough about the role of clouds in global warming/cooling. (Although it is fairly certain that low clouds have a cooling effect and high clouds have a warming effect.)

Apart from the cosmic rays there are other sources. Dimethyl sulphide aerosols, emitted into the air by phytoplankton in the ocean, and sulphuric acid and ammonia aerosols also affect cloud formation in ways which are not fully understood. There is also some evidence that the intensity of the cosmic ray stream itself varies over very long periods according to the position of the Earth in the Milky Way (i.e. the spiral galaxy of which the sun is part). 

So don’t blame the climate scientists if they have disagreements about the degree of global warming we can expect over the coming decades.  What cannot be denied is that most of them agree that man’s input to the weather system has caused much of the global warming since the Industrial Revolution of the 1800s.

Warming causes floods, droughts and storms. So the more we can do to stop it, or at least offset it, the better and to do this effectively requires the best possible understanding of all the influences – natural or artificial.

Author, 2077 AD