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Cloud forecasting and Cosmic rays

Paul Hudson | 14:26 UK time, Friday, 13 November 2009

Despite the extent of our knowledge on clouds, and how powerful the computer is that helps us formulate our forecasts, we still do not seem to be able to forecast cloud amounts with any reasonable consistency.

Sometimes the computer models are wrong only six hours ahead! And there can be no doubt about it, cloud has an enormous role to play in calculating temperature levels, and forecasting its extent correctly is at times a major challenge.

Most scientists believe that greenhouse gases are largely responsible for temperature rises particularly during the second half of the last century. But if cloud is so important in predicting global temperature levels, how can we have confidence in projections fifty years ahead when cloud detail for short term forecasts can often prove elusive?

Thinking about clouds reminded me of a seperate, relatively poorly understood and controversial branch of climate change science; cosmic rays.

It's thought by some that cosmic rays can cause changes in cloud cover, by creating condensation nucleii, the very seeds of clouds around which water molecules are attracted to form clouds.

When the sun is active, so the theory goes, its magnetic field is stronger and so better at shielding us against the cosmic rays coming from outer space, before they reach our planet. High solar activity means fewer condensation nucleii and so fewer clouds and, if the theory is correct, a warmer world. Low solar activity and poorer shielding against cosmic rays result in increased cloud cover and hence a cooling. By regulating the Earth's cloud cover, it's thought the sun may turn the temperature up and down.

As the sun's magnetism increased in strength (higher sunspot activity) during the twentieth century, its thought that this natural mechanism may be responsible for at least some of global warming seen during the last century, as a result of decreased cloud cover.

But successive pieces of research has failed to find any link between cosmic rays and cloud. Mike Lockwood, from the UK's Rutherford-Appleton Laboratory, found no link in the last forty years.

More recently a University of Lancaster team found no significant link between cosmic rays and cloudiness in the last twenty years.

But in a paper by Henrik Svensmark and Eigil Friis-Christensen, at the Danish National Space centre, they claim that there is a link between cosmic rays and global temperatures. See diagram below.

PHgraph121109.jpg

So the arguments go on as to what effects cosmic rays have on temperature levels. There is very little in the IPCC report on the subject, but its difficult not to conclude looking at the above graph that there is an obvious link between temperatures and cosmic rays - even if the mechanism is poorly understood.

The idea that cosmic rays do impact us on earth by affecting our climate has been recently given a boost by research conducted last month into tree growth. The researchers tried to correlate tree growth to solar activity (hence cosmic rays) - and found a link.

According to them, an increase in cloud cover and haze would diffuse the amount of solar radiation reaching the trees. As diffuse radiation penetrates forest canopies better than direct light, it would increase the amount of radiation that plants capture, and increase photosynthesis by trees, boosting growth.

It would seem that it may well be in everyone's best interests to conduct more research into this intriguing branch of solar and climate science.

(Please note: Text highlighted in blue links to relevent research)

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