Two events loom on the horizon that might settle the issue once and for all; one shaped by human hands, one entirely natural.
At Cern, the giant European physics facility, an experiment called Cloud is being constructed which will research the notion that cosmic rays can stimulate the formation of droplets and clouds. There may be some results within three or four years.
By then, observations suggest that the Sun’s output may have started to wane from its “grand maximum”.
If it does, and if Henrik Svensmark is right, we should then see cosmic rays increase and global temperatures start to fall; if that happens, he can expect to see a Nobel Prize and thousands of red-faced former IPCC members queuing up to hand back the one they have just received.
But if the Sun wanes and temperatures on our planet continue to rise, as the vast majority of scientists in the field believe, the solar-cosmic ray concept of global warming can be laid to eternal rest.
BBC News website: Sun and global warming: A cosmic connection?