Contribution of CO2 is around 76% in Green House Gases..and as i 'ev read some sources U.S. emits more than any other country in the world accounting for 25% of all,still its not officially declared..
Check this link for more information on Global Warming ..

http://www.buzzle.com/articles/global-warming/

To say the truth without offensing anyone and according to the findings USA is the most green house gas emitting country in the world as it is the most developed nation in tyhe world so, but naturally it has more industries and are emitting the most amount of green house gases.

Read more: http://wiki.answers.com/Q/Which_country_emits_the_most_greenhouse_gases_per_person#ixzz1GrvqlXPQ

Probily the united states and china

The america gives more pollution than china

YO MAMA