Sun is “not causing global warming”

Two North American scientists say a controversial hypothesis that the sun may impact global warming has been laid to rest, Science reported. They tested the idea that increased solar activity reduces cloudiness by changing cosmic rays, and that the reduced cloud cover let in more sunlight, causing the earth to warm. Their conclusion: the changes are far too small to affect climate.

Peter Adams of Carnegie Mellon University and Jeff Pierce of Dalhousie University developed a model to test the hypothesis that changes in the sun are causing global warming. Some climate-change skeptics have tried to use the hypothesis to suggest that greenhouse gases may not be the global-warming culprits that most scientists agree they are.

In research published in Geophysical Research Letters, Adams and Pierce report the first atmospheric simulations of changes in atmospheric ions and particle formation resulting from variations in the sun and cosmic rays. While acknowledging that no computer simulation of something so complex can be perfect, they found that changes in the concentration of particles that affect clouds were 100 times too small to affect the climate.

“Until now, proponents of this hypothesis could assert that the sun may be causing global warming because no one had a computer model to really test the claims,” Adams said. “The basic problem with the hypothesis is that solar variations probably change new particle formation rates by less than 30% in the atmosphere. Also, these particles are extremely small and need to grow before they can affect clouds. Most do not survive to do so.”

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