Answer
It is the best to say: "The majority of Americans believe that there is evidence of global warming."
Work Step by Step
A survey of $1501$ people is quite large, but it is still a really small portion of 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.) Hence if writing an article, it is the best to say: "The majority of Americans believe that there is evidence of global warming."
