Sun, cloudiness and global warming not intertwined


Climate change

Sun through clouds

Credit: Wikimedia

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A troubling suggestion about how the sun may impact global warming is thought to be laid to rest.

There has been a lingering suspicion among some that increased solar activity can reduce cloudiness by changing cosmic rays - and with a decrease in clouds comes an increase in sunlight being let in, potentially leading to a warming of the Earth.

Some climate change skeptics have tried to use this idea to suggest that greenhouse gases may not be the global warming culprits that most scientists agree they are.

In research recently published in Geophysical Research Letters, two North American scientists reported the first simulations of changes in atmospheric particles as the result of variations in the sun and cosmic rays.

They found that changes in the concentration of particles that affect clouds are 100 times too small to affect the climate.

"Until now, proponents of this [warming theory] could assert that the sun may be causing global warming because no one had a computer model to really test the claims," said study co-author Peter Adams, an environmental engineer at Carnegie Mellon University in the US.

"The basic problem with the [idea] is that solar variations probably change new particle formation rates by less than 30 percent 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," Adams said.

Despite remaining questions, the researchers feel confident that the 'cloudiness theory' should be laid to rest.

"No computer simulation of something as complex as the atmosphere will ever be perfect," Adams said, adding "proponents of the cosmic ray hypothesis will probably try to question these results, but the effect is so weak in our model that it is hard for us to see this basic result changing."