The poll, called "The Global Index of Religiosity and Atheism," found that the number of Americans who say they are "religious" dropped from 73 percent in 2005 (the last time the poll was conducted) to 60 percent.
At the same time, the number of Americans who say they are atheists rose, from 1 percent to 5 percent.
The poll was conducted by WIN-Gallup International and is based on interviews with 50,000 people from 57 countries and five continents. Participants were asked, "Irrespective of whether you attend a place of worship or not, would you say you are a religious person, not a religious person, or a convinced atheist?"
The seven years between the polls is notable because 2005 saw the publication of "The End of Faith" by Sam Harris, the first in a wave of best-selling books on atheism by Christopher Hitchens, Richard Dawkins, Daniel Dennett and other so-called "New Atheists."
"The obvious implication is that this is a manifestation of the New Atheism movement," said Ryan Cragun, a University of Tampa sociologist of religion who studies American and global atheism.
Still, Cragun does not believe the poll shows more people are becoming atheists, but rather that more people are willing to identify as atheists.
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Another possible factor may be the number of atheists within organized efforts by American atheist groups to encourage those who do not believe in God to say so publicly. The Out Campaign, a project of the Richard Dawkins Foundation for Reason and Science, was launched in 2007 and has since been endorsed by several national atheist groups.
That’s the foundation David Rolfe pledged £20,000 to if they “simply accept the challenge [to show how the shroud might have been ‘faked up’] and follow it through to some kind of conclusion. The public can make up their own minds about the result.”