More than three in four Americans agree that global warming is happening, and about six in 10 understand that it is mostly owing to human activity, but only about one in four know that nearly all climate scientists agree that global warming is happening as a result of human activity. Those were among the key findings of Climate Change in the American Mind: September 2021 (PDF).
Presented with a definition of global warming as "the idea that the world's average temperature has been increasing over the past 150 years, may be increasing more in the future, and that the world's climate may change as a result" and asked whether they thought that global warming is happening, 76% of respondents said yes, 12% said no, and 11% indicated that they didn't know.
Asked about the cause of global warming, on the assumption that it is happening, 60% of respondents said that it is caused mostly by human activities, 26% said that it is caused mostly by natural changes in the environment, 5% opted for "neither because global warming isn't happening," and 9% volunteered a different response.
Asked to indicate "what percentage of climate scientists think that human-caused global warming is happening," only 24% of respondents selected a value between 91% and 100% — the correct range, as repeated independent studies have demonstrated. In the first year in which the question was asked, 2013, only 6% of respondents selected the correct range.
The study was conducted by the Yale Project on Climate Change Communication and the George Mason University Center for Climate Change Communication. The survey was administered in a web-based environment from September 10 to September 20, 2021, using an online research panel of 1006 American adults.
According to the report, the sample "includes a representative cross-section of American adults — irrespective of whether they have Internet access, use only a cell phone, etc. Key demographic variables were weighted, post survey, to match U.S. Census Bureau norms." The margin of sampling error was plus or minus 3% at the 95% confidence level.