Many Americans skeptical of global warming's immediate impact

The Obama administration will unveil the first-ever carbon pollution limits on existing power plantsMonday and according to a recent CBS News Poll, while most Americans express concern about global warming, many aren't feeling a great sense of urgency about its impact.

The poll, conducted last month, found fewer than half of Americans (46 percent) think global warming is having a serious impact now. Another 31 percent don't expect a serious impact until sometime in the future, and one in five doesn't think global warming will have a serious impact at all.

Opinions on the seriousness of global warming have wavered little in recent years, but there are stark demographic differences on the issue. A majority of college graduates (60 percent) believe global warming is a problem that is having an effect right now, but that number drops to 40 percent among those without a college degree. Older Americans are less likely than those who are younger to think global warming's impact is urgent. Politics plays a role as well: Democrats (65 percent) are more than twice as likely as Republicans (28 percent) to say global warming is causing an impact now.

Looking deeper, Americans' opinions on what primarily causes global warming also influence how pressing they think it is. Those who say global warming is mostly caused by human activity (about half of Americans) are especially likely to think the effects of global warming are more urgent - 72 percent of this group says it is having a serious impact right now. Americans who say global warming is caused mostly by natural patterns in the earth's environment (a third of the public) are more inclined to think its impact will occur sometime in the future; only 26 percent think it is being felt now.

Still, overall, most Americans express at least some concern about global warming (66 percent), only a third are not too or not at all concerned about it.