BEIJING, Oct. 21 (Xinhuanet) -- Most Americans think emissions from cars and industrial plants should be the primary cause of global warming and the United States should reduce their levels, according to a survey quoted by media reports Sunday.

The survey, conducted by the CNN/Opinion Research Corp. poll, showed 56 percent of respondents said the phenomenon of global warming has been proven, and can be largely blamed on human endeavors, such as power plants and factories.

In comparison, 21 percent claimed global warming problems are caused either by natural changes or are unproven.

Also, 66 believed the United States should do what it can to reduce global warming, even if other nations ignore it. This compares with 52 percent of respondents who believed that way in 2001.

The survey of 1,212 adults was conducted Oct. 12-14 and has a sampling error of plus or minus 4.5 percentage points.

(Agencies)