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Friday, February 13, 1998 Published at 19:25 GMT
Sci/Tech
Scientists blame sun for global warming
The Sun is more active than it has ever been in the last 300 years
Climate changes such as global warming may be due to changes in the sun rather than to the release of greenhouse gases on Earth.
Climatologists and astronomers speaking at the American Association for the Advancement of Science meeting in Philadelphia say the present warming may be unusual - but a mini ice age could soon follow.
The sun provides all the energy that drives our climate, but it is not the constant star it might seem.
Careful studies over the last 20 years show that its overall brightness and energy output increases slightly as sunspot activity rises to the peak of its 11-year cycle.
And individual cycles can be more or less active.
The sun is currently at its most active for 300 years.
That, say scientists in Philadelphia, could be a more significant cause of global warming than the emissions of greenhouse gases that are most often blamed.
The researchers point out that much of the half-a-degree rise in global temperature over the last 120 years occurred before 1940 - earlier than the biggest rise in greenhouse gas emissions.
Ancient trees reveal most warm spells are caused by the sun
Using ancient tree rings, they show that 17 out of 19 warm spells in the last 10,000 years coincided with peaks in solar activity.
They have also studied other sun-like stars and found that they spend significant periods without sunspots at all, so perhaps cool spells should be feared more than global warming.
The scientists do not pretend they can explain everything, nor do they say that attempts to reduce greenhouse gas emissions should be abandoned. But they do feel that understanding of our nearest star must be increased if the climate is to be understood.
BBC
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