WASHINGTON (Reuters) - A growing number of Americans, nearly half the country, think global warming worries are exaggerated and more people doubt that scientific warnings of severe environmental fallout will ever occur, according to a new Gallup poll.

A woman walks through heavy snow as she carries her coffee on Capitol Hill in Washington, February 11, 2010. REUTERS/Jason Reed

The new doubts come as President Barack Obama pressures Congress to produce legislation significantly cutting smokestack emissions of carbon dioxide and other greenhouse gases blamed for climate change problems.

Gallup’s survey was released on the same day that the Obama administration unveiled in Texas a public-private report underscoring threats to birds as climate change alters their habitat and food supply, pushing many species to extinction.

With congressional elections in November, many lawmakers are hesitant to take on a controversial energy and environment bill, especially if voter interest is waning.

Around the world, concerns about climate change have dipped as economic worries took higher priority, according to a Nielson/Oxford University survey in December, which found the highest concern was in Latin America and Asia-Pacific countries like the Philippines, where typhoons are a big threat.

While U.S. worries about climate change fell significantly in the Nielson poll, they did not come close to some eastern European countries such as Estonia, which ranked bottom.

In response to escalating attacks from global warming skeptics, the Union of Concerned Scientists on Thursday released a letter they said was signed by more than 2,000 climate scientists and economists, including some Nobel prize winners, urging the U.S. Senate to pass a climate change bill.

“The strength of the science on climate change compels us to warn the nation about the growing risk of irreversible consequences ... as temperatures rise further, the scope and severity of global warming impacts will continue to accelerate,” they wrote.

The Gallup poll, conducted March 4-7, indicates a reversal in public sentiment on an issue that not only involves the environment, but also economic and national security concerns.

Forty-eight percent of Americans now believe that the seriousness of global warming is exaggerated, up from 41 percent last year and 31 percent in 1997, when Gallup first asked the question.

The survey follows reports that some of the scientific details of findings that went into international global warming reports were either flawed or exaggerated.

Supporters of a global effort to keep the Earth’s temperatures from rising more than 2 degrees Celsius from pre-industrial levels agree that scientists need to be more fastidious in their research, but there is overwhelming evidence that a warming planet will lead to ice melting, flooding, drought, refugees and the spread of disease.

The United States has made a non-binding pledge to seek a 17 percent reduction in carbon emissions by 2020, from 2005 levels, mostly by switching to alternative energy, such as wind and solar power. But without legislation from Congress, that goal is unlikely to be met.

The Gallup poll of slightly more than 1,014 adults has a sampling error margin of plus or minus 4 percent.

A majority still believes global warming is real but that percentage is falling, with the average American now less convinced than at any time since 1997.

Thirty-five percent said in the latest poll that the effects of global warming either will never happen (19 percent) or will not happen in their lifetimes (16 percent).