July 11 (Bloomberg) -- Recent global warming isn't a result of solar radiation, scientists said, disputing a theory advanced by some researchers as an alternative to the United Nations' view that temperatures are rising as a result of human activities.

The scientists examined historical records of solar activity over the past century, studying measures such as the number of sunspots and the amount of light emitted. They found that the total radiation from the sun peaked in 1985, according to Mike Lockwood, co-author of the paper published today in the U.K. journal Proceedings of the Royal Society A.

``The sun did a U-turn around 1985, but the temperatures kept on rising,'' Lockwood, a solar physicist at the Rutherford Appleton Laboratory in Chilton, central England, said late yesterday in a telephone interview. ``Everything on the sun that could have affected climate has been going in the wrong direction to cause warming, and we've seen continued warming.''

The findings contradict scientists who posit that the sun is the main cause of recent warming, rather than human emissions of greenhouse gases such as carbon dioxide. The discovery also goes against the central arguments of ``The Great Global Warming Swindle,'' a documentary aired earlier this year by the U.K.'s Channel 4 television station.

Henrik Svensmark, a scientist at the Danish Space Research Institute in Copenhagen, has published a series of papers drawing links between cosmic rays and global warming. Svensmark's secretary said he wasn't available to comment on today's paper. Philip Stott, a retired University of London professor who said in March he thought the cosmic rays theory of global warming would supplant the greenhouse gases viewpoint, said today he couldn't comment on the latest paper because he hasn't read it.

Hottest Years

Global warming is the process by which gases in the atmosphere, including carbon dioxide produced by burning fossil fuels, trap heat radiating from the Earth. That may result in an increase in extreme weather events such as floods, droughts and typhoons.

The UN Intergovernmental Panel on Climate Change this year has said the global average temperature has risen by 0.76 degree Celsius since the mid-nineteenth century, with 11 of the 12 hottest years ever coming since 1995.

Lockwood, also a professor at Southampton University, worked with Claus Froehlich at the World Radiation Center in Davos, Switzerland, to study different measures of solar activity.

The two scientists found that the number of sunspots and the total irradiance, or power, emitted by the sun, peaked in 1985.

Two other measures they studied are the so-called solar flux, a magnetic field that shields the Earth, and cosmic rays, which are produced by explosions of supernovae, and which produce neutrons when they enter the atmosphere. The flux shields the atmosphere from the rays, and Lockwood and Froehlich found the flux peaked in 1987, and the number of cosmic rays reached a minimum at the same time, both indications that since then, solar activity has diminished.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: July 11, 2007 06:52 EDT