What has CLOUD discovered and why is it important for our understanding of climate? There are several important discoveries from CLOUD. Firstly, we have shown that the most likely nucleating vapours, sulphuric acid and ammonia, cannot account for nucleation that is observed in the lower atmosphere. The nucleation observed in the chamber occurs at only one‐tenth to one‐thousandth of the rate observed in the lower atmosphere. Based on the first results from CLOUD, it is clear that the treatment of aerosol formation in climate models will need to be substantially revised, since all models assume that nucleation is caused by these vapours and water alone. It is now urgent to identify the additional nucleating vapours, and whether their sources are mainly natural or from human activities.
I am slightly confused about this though - are we saying that the models include a factor for nucleation that is equal to the rate of nucleation currently observed, and which changes based on how we think sulphuric acid and ammonia levels in the atmosphere will change in future? Or are we saying that the level of nucleation in the models is 10--1000 times too small? I assume the former, but I had also believed that the models went back to first physical principles rather than using empirical measures.
Maybe somebody can put me right here?
David Whitehouse has more.