Alternative climate-change theory.

For the last decade, scientist Henrik Svensmark of the Danish Space Research Institute and his collaborators have been piecing together evidence supporting a novel theory that may spark a paradigm shift in how climate change is understood. According to Svensmark, the key to understanding the Earth's climate does not lie with human release of greenhouse gases, but can actually be found among the stars.

In a 1999 paper entitled "Cosmic Rays and the Earth's Climate," Svensmark discussed the impact of "galactic cosmic rays" (GCR) on climate. "Recently it was found that the Earth's cloud cover, observed by satellites, is strongly correlated with GCR," he wrote, noting that galactic cosmic rays play a role in cloud formation. According to Svensmark, when the sun is in a more active state (as it has been in recent years), solar influences deflect a greater amount of cosmic radiation, causing a reduction in cloud cover that allows more solar radiation to penetrate and heat the atmosphere. Periods of low solar activity lead to the opposite effect and a cooler climate. In his 1999 paper, Svensmark concluded that "a solar influence on clouds could be the main cause for the observed correlations between the sun and Earth's climate."

Recently obtained experimental results have buttressed his theory. According to Seed, a science magazine, "Svensmark recreated the gas chemistry of Earth's atmosphere in a plastic chamber and used UV lamps to simulate the Sun's rays. Cosmic rays from above also penetrated the chamber while instruments measured how these rays interacted with the gas mixture."

Svensmark's results, which have been published in the Proceedings of the Royal Society, remain controversial but may revolutionize climate science--a field that has lacked a thorough understanding of the effects of cloud cover. "Now after studying this for 10 years, I think it's completely certain that solar activity ... is changing the Earth's climate," Svensmark told Seed.