Most leading climate experts don’t agree with Henrik Svensmark, the 49-year-old director of the Center for Sun-Climate Research at the Danish National Space Center in Copenhagen. In fact, he has taken a lot of blows for proposing that solar activity and cosmic rays are instrumental in determining the warming (and cooling) of Earth. His studies show that cosmic rays trigger cloud formation, suggesting that a high level of solar activity—which suppresses the flow of cosmic rays striking the atmosphere—could result in fewer clouds and a warmer planet. This, Svensmark contends, could account for most of the warming during the last century. Does this mean that carbon dioxide is less important than we’ve been led to believe? Yes, he says, but how much less is impossible to know because climate models are so limited.

There is probably no greater scientific heresy today than questioning the warming role of CO2, especially in the wake of the report issued by the United Nations Intergovernmental Panel on Climate Change (IPCC). That report warned that nations must cut back on greenhouse gas emissions, and insisted that “unless drastic action is taken . . . millions of poor people will suffer from hunger, thirst, floods, and disease.” As astrophysicist Eugene Parker, the discoverer of solar wind, writes in the foreword to Svensmark’s new book, The Chilling Stars: A New Theory of Climate Change, “Global warming has become a political issue both in government and in the scientific community. The scientific lines have been drawn by ‘eminent’ scientists, and an important new idea is an unwelcome intruder. It upsets the established orthodoxy.”

We talked with the unexpectedly modest and soft-spoken Henrik Svensmark about his work, the criticism it has received, and truth versus hype in climate science. http://discovermagazine.com/2007/jul/the-discover-interview-henrik-svensmark