That is great. It's nice to have famous, respected scientists pointing to the very real danger of increased global temperatures and the changes that accompany it. What bugged me though takes some background explaining.
The field of study I am in has ties to the climate change field; we study the effect of the sun on the earth though we are supported by the same research council as astronomy (solar system science is packaged as a subset of astronomy). The real astronomers outnumber us significantly and recently it was decided that a lot of what we do was less important than other areas and consequently funding (which is low overall) was cut. This, of course, limits our ability to monitor and understand how the sun affects the Earth. Add to this that for years it has been difficult (impossible?) to get the research councils who support our activity to work hand-in-hand with the research council who support things like lower atmospheric science so that we can accomplish real joined-up thinking.
So it is a little galling that on this background we see the most famous theoretical astrophysicist/cosmologist talking about how important climate change is.