More and less snow on the roof of Europe

 Earlier this week I was at scientific meeting on how water freezes, a key problem in understanding how the  cold clouds and snow form. The very last talk I caught before I had to leave to catch my train, showed some striking data. We know that ice and snow in the atmosphere almost always start to form not just from water on its own, but from water in contact with a tiny particle in the atmosphere. So the number of these particles and their surface properties greatly influence how clouds and snow form. If, for whatever reason, there are many of these particles in the air, we may get more snow.

So the PhD student giving the talk had been dispatched to the Jungfraujoch in the Swiss alps to measure the amounts of these tiny particles. Her interesting, but awkward, observation is that there is no typical concentration of these tiny particles in the Alpine air. The concentration of particles on Tuesday could be ten or more times their concentration on Monday.

The reason for this variation is our atmosphere is one big connected system. When you look at the picture of the Alps at the top, your first thought is probably not: lots of snow, this must be due to a dust storm. But hundreds or thousands of kilometres from the Jungfraujoch, there will be a dust storm which sucks huge numbers of tiny particles into the atmosphere, and maybe a week later this air turns up high in the alps, and helps make snow.

This is a beautiful illustration of how connected our atmosphere and climate is, but in practical terms it makes modelling our climate a nightmare. If snowfall is at least partially controlled by the concentration of these particles and this concentration varies by huge amounts from day to day and mountain to mountain, due to dust storms half a world away, then getting all that detail in a model is essentially impossible. Modern computers are powerful, and we have a lot of data, but they are not that powerful, and we don’t have that much data, to include this level of detail. There are real limitations to our ability to predict the future of our climate, so we should probably take a cautious approach to climate change.