PRINCETON, NJ -- Gallup's annual update on Americans' attitudes toward the environment shows a public that over the last two years has become less worried about the threat of global warming, less convinced that its effects are already happening, and more likely to believe that scientists themselves are uncertain about its occurrence. In response to one key question, 48% of Americans now believe that the seriousness of global warming is generally exaggerated, up from 41% in 2009 and 31% in 1997, when Gallup first asked the question.

These results are based on the annual Gallup Social Series Environment poll, conducted March 4-7 of this year. The survey results show that the reversal in Americans' concerns about global warming that began last year has continued in 2010 -- in some cases reverting to the levels recorded when Gallup began tracking global warming measures more than a decade ago.

For example, the percentage of Americans who now say reports of global warming are generally exaggerated is by a significant margin the highest such reading in the 13-year history of asking the question. In 1997, 31% said global warming's effects had been exaggerated; last year, 41% said the same, and this year the number is 48%.

Fewer Americans Think Effects of Global Warming Are Occurring

"In a sharp turnaround from what Gallup found as recently as three years ago, Americans are now almost evenly split in their views of the cause of increases in the Earth's temperature over the last century."

Many global warming activists have used film and photos of melting ice caps and glaciers, and the expanding reach of deserts, to drive home their point that global warming is already having alarming effects on the earth. While these efforts may have borne fruit over much of the 2000s, during the last two years, Americans' convictions about global warming's effects have waned.

A majority of Americans still agree that global warming is real, as 53% say the effects of the problem have already begun or will do so in a few years. That percentage is dwindling, however. The average American is now less convinced than at any time since 1997 that global warming's effects have already begun or will begin shortly.

Meanwhile, 35% say that the effects of global warming either will never happen (19%) or will not happen in their lifetimes (16%).

The 19% figure is more than double the number who held this view in 1997.

In similar fashion, the percentage of Americans who believe that global warming is going to affect them or their way of life in their lifetimes has dropped to 32% from a 40% high point in 2008. Two-thirds of Americans say global warming will not affect them in their lifetimes.

The shift in these views during the past two years has been particularly striking. The percentage who said global warming would pose a serious threat increased gradually from 1997 through 2008. The trend in these responses changed course last year, with slightly fewer Americans saying global warming would have a significant effect in their lifetimes. This year, that percentage is down even more, marking a six-point drop from 2009, and roughly similar to where it was nine years ago.

Americans Divided on Causes of Global Warming

In a sharp turnaround from what Gallup found as recently as three years ago, Americans are now almost evenly split in their views of the cause of increases in the Earth's temperature over the last century.

In 2003, 61% of Americans said such increases were due to human activities -- in line with advocates of the global warming issue -- while 33% said they were due to natural changes in the environment. Now, a significantly diminished 50% say temperature increases are due to human activities, and 46% say they are not.

Americans Less Sure About Scientists' Beliefs

Since last fall, there have been widespread news accounts of allegations of errors in scientific reports on global warming and alleged attempts by some scientists to doctor the global warming record.

These news reports may well have caused some Americans to re-evaluate the scientific consensus on global warming. Roughly half of Americans now say that "most scientists believe that global warming is occurring," down from 65% in recent years. The dominant opposing thesis, held by 36% of Americans, is that scientists are unsure about global warming. An additional 10% say most scientists believe global warming is not occurring.

The percentage of Americans who think most scientists believe global warming is occurring has dropped 13 points from two years ago, and is the lowest since the first time Gallup asked this question back in 1997.

Implications

The last two years have marked a general reversal in the trend of Americans' attitudes about global warming. Most Gallup measures up to 2008 had shown increasing concern over global warming on the part of the average American, in line with what one might have expected given the high level of publicity on the topic. Former Vice President Al Gore had been particularly prominent in this regard, with the publication of his bestselling book, "An Inconvenient Truth," an Academy Award-winning documentary movie focusing on his global warming awareness campaign, and Gore's receipt of a Nobel Peace Prize in 2007.

But the public opinion tide turned in 2009, when several Gallup measures showed a slight retreat in public concern about global warming. This year, the downturn is even more pronounced.

Some of the shifts in Americans' views may reflect real-world events, including the publicity surrounding allegations of scientific fraud relating to global warming evidence, and -- perhaps in some parts of the country -- a reflection of the record-breaking snow and cold temperatures of this past winter. Additionally, evidence from last year showed that the issue of global warming was becoming heavily partisan in nature, and it may be that the continuing doubts about global warming put forth by conservatives and others are having an effect. A forthcoming analysis here at Gallup.com will examine shifts in global warming attitudes in recent years among various demographic and political groups.

Survey Methods

Results are based on telephone interviews with a random sample of 1,014 national adults, aged 18 and older, conducted March 4-7, 2010. For results based on the total sample of national adults, one can say with 95% confidence that the maximum margin of sampling error is ±4 percentage points.

Interviews are conducted with respondents on land-line telephones (for respondents with a land-line telephone) and cellular phones (for respondents who are cell-phone only).

In addition to sampling error, question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.