Svensmark and his colleague had arrived at their theory after examining data that showed a surprisingly strong correlation between cosmic rays --highspeed atomic particles originating in exploded stars in the Milky Way -- and low-altitude clouds. Earth's cloud cover increased when the intensity of cosmic rays grew and decreased when the intensity declined.
Low-altitude clouds are significant because they especially shield the Earth from the sun to keep us cool. Low cloud cover can vary by 2% in five years, affecting the Earth's surface by as much as 1.2 watts per square metre during that same period. "That figure can be compared with about 1.4 watts per square metre estimated by the Intergovernmental Panel on Climate Change for the greenhouse effect of all the increase in carbon dioxide in the air since the Industrial Revolution," Dr. Svensmark explained.
The Danish scientists put together several well-established scientific phenomena to arrive at their novel 1996 theory. The sun's magnetic field deflects some of the cosmic rays that penetrate the Earth's atmosphere, and in so doing it also limits the immense amounts of ions and free electrons that the cosmic rays produce. But something had changed in the 20th century: The sun's magnetic field more than doubled in strength, deflecting an extraordinary number of rays. Could the diminution of cosmic rays this century have limited the formation of clouds, making the Earth warmer?
That was a plausible theory. But exactly how cosmic rays might create clouds was a mystery -- an unprovable theory, many said. Some even claimed that it was inconceivable for cosmic rays to influence cloud cover.
To discover a mechanism, a team at the Danish National Space Center assembled by Dr. Svensmark undertook an elaborate laboratory experiment in a reaction chamber the size of a small room. The team duplicated the chemistry of the lower atmosphere by injecting the gases found there in the same proportions, and adding ultraviolet rays to mimic the actions of the sun.
What they found left them agape: A vast number of floating microscopic droplets soon filled the reaction chamber. These were ultra-small clusters of sulphuric acid and water molecules -- the building blocks for cloud condensation nuclei-- that had been catalyzed by the electrons released by cosmic rays.
Saturday, January 06, 2007
20TH CENTURY CLIMATE CHANGES CAUSED BY THE SUN
As reported in the National Post (Hat Tip: Tim Blair), Henrik Svensmark, Director of the Centre for Sun-Climate Research at the Danish Space Research Institute, has recently published experimental evidence supporting his 1996 theory that "the sun and the stars could explain most if not all of the warming this century":
Posted by Punditarian at 6:13 PM