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Sun in frenzy since 1940
30/10/2003 07:41 - (SA)
Hamburg - German scientists who have created a 1 000-year- record of sunspots said on Wednesday they discovered the Sun has been in a frenzy since 1940 and this may be a factor in global warming.
The research, based on the quantities of the isotope beryllium 10 found in ice bores from Greenland and the Antarctic, challenges the belief that carbon dioxide from cars and coal fires and other greenhouse gases are the only cause of recent warmer climates.
The team from the Max Planck Institute for Aeronomy in Germany and Finland's Oulu University discovered a past phase of elevated sunspot activity between 1100 and 1250, though there were far fewer sunspots then than today.
The Earth was very warm at that time and Vikings were recorded as farming on Greenland.
Early 17th century
A gas cloud from one of the largest flares ever seen on the Sun reached the Earth this week causing a magnetic storm that disrupted radio and radar systems, forcing safety authorities to space out airline traffic. More flares and disruption are expected.
The findings, which are to appear in the December issue of Physical Review Letters, chart sunspots back to the year 850. Sunspots were first observed in the early 17th century after the discovery of the telescope.
Astronomers have made on-again-off-again notes ever since of the spots, where the Sun's surface appears darker because magnetic fields disrupt the outflow of energy from the star's interior. Most of the surface is 5 800 degrees celsius, but a spot is 1 500 degrees colder.
The 11-year cycle of sunspots from strong to weak to strong again is well known to anyone using shortwave radio, but the long-term fluctuation was not plain.
The team said the surge of spots and gas flares since 1940 was the greatest in the entire period checked. The activity was 2.5 times the long-term average. Solar activity matched average temperatures on the Earth, they added.
New climate influence
Radioactive beryllium 10 used for the readings comes from cosmic rays bombarding nitrogen and oxygen in the air. The element falls to the ground with rain and snow. Layers are preserved in the ice caps.
Sunspots block cosmic rays from reaching the Earth, meaning less beryllium and increased ultraviolet radiation.
The statement on Wednesday noted a much-discussed Danish hypothesis suggesting cosmic radiation helps tiny particles to form in air, increasing cloud formation. Sunspots would thus mean fewer clouds.
Sami K Solanki, director of the German institute, said the team had discovered a new climate influence, but still believed recent climate change was mainly the result of mankind using more and more fossil fuels.
"Even after our findings, I would say the sharp increase in global temperatures since 1980 can still be mainly attributed to the greenhouse effect arising from carbon dioxide," professor Solanki said. - Sapa-dpa
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