The performance index is calculated by "GermanWatch".
Climate Change Performance Index 2008
This link gives access to tables, videos and previous years data.
Green Daily provide some commentary and a summary table (to save me doing it).
Climate Change Performance Index 2008 released [Green Daily]
The index compares the relative performance of 56 countries in combating climate change, taking into account not only current emissions, but emissions trends and governmental policy. Not surprisingly, the US did poorly, ranking 55th, ahead of only Saudi Arabia and 15 spots below fellow greenhouse gas giant China. However, Americans aren't alone down there - particularly alarming is that of the top 10 gassers, 7 of them are below 40th place in the list, meaning in general that they have no practical strategy for, or intention of, reducing emissions anytime soon.