A strange story on the BBC today about a team of people in peru who are painting mountains white in order to encourage the return of glaciers to their mountains. Truly the story is sad.
First the physics. Yes, it is true that painting the mountain white will cause more sunlight to be reflected and will cool the average surface temperature of the mountain. If the average surface temperature is just above zero degrees Celsius then the paint may cause the average temperature to fall below zero and allow ice to form and snow to settle. And could this cause a glacier to re-form? Well, No.
Why not? Well one only needs to reflect on the fact that a glacier did exists there previously and that it was on top off the rocks. At some point in history – probably only 100 years ago – it would have presented an extraordinarily white reflective surface to the Sun. The surface would have been far smoother and more reflective than any surface finish that could be achieved by throwing buckets of lime on the rocks. And yet the slow action of climate change and possible industrial soot caused the destruction of the glacier in just a hundred years or so.
So let us imagine that the white paint caused ice to reform and survive over the summer at this location. The paint would then be irrelevant – and exactly the same climate forces which destroyed the previous glacier will destroy the the next one.
And so to me this story is just sad, sad, sad. The glacier is gone; the spring water it supplied is gone; and it is not coming back anytime soon. The residents would be better employed building a dam to create an artificial lake that would trap some of the winter melt water.