Lots of data is packed into this simple interface, and the map itself is blessedly clear.
Note, though, that when it comes to infoviz issues, even these pros needed a do-over. Check out the message in the lower left corner. In an earlier version they made the common mistake of comparing circles based on radius, instead of by area. It's to their credit that not only did they fix the mistake, but they also owned up to it and made the change. The larger problem, though, is that distinguishing the relative size of circles is not easy for the average viewer; rectangles are clearer, and would probably have made this cool map even stronger.
Note also that stats are from 2005. Since then there's been substantial economic growth in China (for example), so the current numbers are likely to be even higher than what's shown here.
Differing Views Cloud Climate Talks — Center for Public Integrity