This study conducted by Yale University in 2005 measured environmental sustainability by country.  The United States ended up with a rating below most of the advanced nations, and also below many of the smaller, less fortunate among us.

http://www.yale.edu/esi/ESI2005_Main_Report.pdf

Given the fact that we are capable of just about anything when we put our muscle behind it, the greatest country on earth will no doubt improve on this number in the coming decades.  Go USA!