In a national survey completed in November 2011, we found that a large majority of Americans (66%) support signing an international treaty requiring the US to cut emissions 90% by 2050:
Breaking the result down by political party (among registered voters), we found that large majorities of Democrats (81%) and Independents support such a treaty (61%), while almost half of Republicans support such a treaty (49%).
Source: Public Support for Climate & Energy Policies in November 2011