The sun is burning hotter than usual, offering a possible explanation for global warming that needs to be weighed when proceeding with expensive efforts to cut emissions of greenhouse gases, Swiss and German scientists say.
"The sun has been at its strongest over the past 60 years and may now be affecting global temperatures," said Sami Solanki, the director of the renowned Max Planck Institute for Solar System Research in Gottingen, Germany, who led the research.
"The sun is in a changed state. It is brighter than it was a few hundred years ago and this brightening started relatively recently -- in the last 100 to 150 years," Mr. Solanski said.
Average global temperatures have increased by about 0.2 degrees Celsius (0.36 degrees Fahrenheit) over the past 20 years and are widely believed to be responsible for new extremes in weather patterns.
Globally, 1997, 1998 and 2002 were the hottest years since worldwide weather records were first collated in 1860.
Bill Burrows, a climatologist and a member of the Royal Meteorological Society, welcomed Mr. Solanki's research.
"It shows that there is enough happening on the solar front to merit further research. Perhaps we are devoting too many resources to correcting human effects on the climate without being sure that we are the major contributor," he said.
Mr. Solanki said that the brighter sun and higher levels of so-called "greenhouse gases" both contributed to the change in the Earth's temperature, but it was impossible to say which had the greater impact.
Most scientists agree that greenhouse gases such as carbon dioxide from fossil fuels have contributed to the warming of the planet in the past few decades, but have questioned whether other factors beyond man's control are also to blame.
To determine the sun's role in global warming, Mr. Solanki's research team measured magnetic zones on the sun's surface known as sunspots, which are believed to intensify the sun's energy output.
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