Answer
I would write that the majority of Americans believe that there is evidence of global warming.
Work Step by Step
While a survey of 1501 people is fairly large, it is not large enough considering a general population of over 240 million people to make any statements regarding the actual numbers in the survey. (After all, given the error, it is hard to state a specific percentage of Americans that the believe that global warming exists.) Thus, if writing an article, it would be best to simply say: "The majority of Americans believe that there is evidence of global warming."
