You were hoping for an erudite discussion of one of the works of Aristophanes? Not today. Instead we are going to look at how clouds and cosmic rays influence our weather and more importantly, climate.

Every one who has looked into the subject knows that climate science is no longer much about science. It is about politics.

When politicians and journalists declare that the science of global warming is settled, they show a regrettable ignorance about how science works. We were treated to another dose of it recently when the experts of the Intergovernmental Panel on Climate Change issued the Summary for Policymakers that puts the political spin on an unfinished scientific dossier on climate change due for publication in a few months' time. They declared that most of the rise in temperatures since the mid-20th century is very likely due to man-made greenhouse gases.

Twenty years ago, climate research became politicised in favour of one particular hypothesis, which redefined the subject as the study of the effect of greenhouse gases. As a result, the rebellious spirits essential for innovative and trustworthy science are greeted with impediments to their research careers. And while the media usually find mavericks at least entertaining, in this case they often imagine that anyone who doubts the hypothesis of man-made global warming must be in the pay of the oil companies. As a result, some key discoveries in climate research go almost unreported.

The best measurements of global air temperatures come from American weather satellites, and they show wobbles but no overall change since 1999.

That levelling off is just what is expected by the chief rival hypothesis, which says that the sun drives climate changes more emphatically than greenhouse gases do. After becoming much more active during the 20th century, the sun now stands at a high but roughly level state of activity. Solar physicists warn of possible global cooling, should the sun revert to the lazier mood it was in during the Little Ice Age 300 years ago.

Climate history and related archeology give solid support to the solar hypothesis. The 20th-century episode, or Modern Warming, was just the latest in a long string of similar events produced by a hyperactive sun, of which the last was the Medieval Warming.

Well we have a new candidate. Cosmic rays. Or the lack of them actually.

Disdain for the sun goes with a failure by the self-appointed greenhouse experts to keep up with inconvenient discoveries about how the solar variations control the climate. The sun's brightness may change too little to account for the big swings in the climate. But more than 10 years have passed since Henrik Svensmark in Copenhagen first pointed out a much more powerful mechanism.

He saw from compilations of weather satellite data that cloudiness varies according to how many atomic particles are coming in from exploded stars. More cosmic rays, more clouds. The sun's magnetic field bats away many of the cosmic rays, and its intensification during the 20th century meant fewer cosmic rays, fewer clouds, and a warmer world. On the other hand the Little Ice Age was chilly because the lazy sun let in more cosmic rays, leaving the world cloudier and gloomier.

The only trouble with Svensmark's idea -- apart from its being politically incorrect -- was that meteorologists denied that cosmic rays could be involved in cloud formation. After long delays in scraping together the funds for an experiment, Svensmark and his small team at the Danish National Space Center hit the jackpot in the summer of 2005.

In a box of air in the basement, they were able to show that electrons set free by cosmic rays coming through the ceiling stitched together droplets of sulphuric acid and water. These are the building blocks for cloud condensation. But journal after journal declined to publish their report; the discovery finally appeared in the Proceedings of the Royal Society late last year.

In Global Cooling I looked into how the sun powers our short term climate cycles. Longer term climate cycles appear to be driven by orbital mechanics such as the roundness of Earth's orbit around the sun and global wobble which changes the angle the Earth presents to the sun. Those are well known and are called Milankovitch Cycles.

There is another factor which needs attention. The Earth's magnetic field waxes and wanes. Currently we are in a waning phase. It has declined about 10% in the last 160 years.

I suppose that will give "the sky is falling" folks something new to be scared to death about and some new reason for them to declare that we have to raise taxes to have the money to fix the problem.

Some things never change.

You can read more about clouds, cosmic rays, and climate change at The U.K. Telegraph

Update: 13 Feb '007 1053z

Donalds Sensing discusses the issue with lots of charts, graphs, and pretty pictures of the sun.

H/T Instapundit

Cross Posted at Power and Control