We still don't even really know exactly how clouds work :
Results from an experiment built to study how clouds form suggests that our knowledge of this subject may need to be revised, Nature journal reports.The Full Story Is Here
Tiny particles (aerosols) form the basis of the "seeds" from which clouds grow.
These seeds form when sulphuric acid and ammonia molecules cluster together - and cosmic rays may help this happen.
But these ingredients create only a tiny fraction of the cloud seeds formed in the atmosphere.
The result surprised Dr Jasper Kirkby who led the research. He told BBC News: "We've shown sulphuric acid and ammonia can't account for nucleation (the very early stages of cloud seed formation) observed in the lower atmosphere.
"We've found that this can only account for a tenth to a thousandth of the rate that's observed. So it's clear from this first set of measurements that our present treatment of aerosols in climate models needs to be revised quite a lot."