I believe this is a good design for several reasons. First, it takes a well-known phenomenon and presents it in a new light. Sure, lots of people talk about how bad global warming is and how we need to get our act together and stop it before it's too late, but they seldom actually describe what the big deal is. Why should we care if the global temperature is rising slowly? People can live in hot places.
This design uses a common graphical concept - an hourglass - to emphasize that time is running out. Within the hourglass is a graphic visualization of how the melting polar ice caps could end up drowning us. The design tugs at our emotions in an effort to make us stop and really think about what's happening.
After all, isn't that the purpose of a design? To make the user stop and think?