On 21 occasions over the past 26 years, Gallup has asked Americans how much they worried about global warming/climate change.
See what they think:

According to the poll results, significantly fewer Americans worry about global warming/climate change now than did fifteen years ago.

In its most recent survey, conducted March 5-8, Gallup asked 1,025 adults whether they worried “a great deal, a fair amount, only a little, or not at all” about a number of environmental issues including “global warming” or “global warming or climate change.”