Americans are becoming more divided in their opinion on impact of global warming and humanity’s role in the phenomenon, as the number of global warming skeptics has roughly doubled over the past 10 years to encompass one in four of the population.

The portion of Americans with mixed opinions about global warming has declined from 49 percent in 2001 to 36 percent today, according to a Gallup poll released on Earth Day Tuesday. Over the same period the number of people who are concerned about global warming and see mankind as its cause has held fairly steady at 39 percent, while the number of people who say they’re “solidly skeptical” of global warming has rocketed from 12 percent in 2001 to 25 percent today.

Women are significantly more likely than men to be concerned about the impact of global warming and humanity’s role in causing it. The age group 30 to 49 is most likely to be concerned about the phenomenon, while younger people aged 18 to 29 are less divided on the issue, least likely to be skeptical and most likely to have mixed views on the matter.

Education is not a good predictor of whether or not a person is concerned about global warming, with about 30% having some college and 30% no college in both groups. Education is a good predictor of whether one falls into the “mixed middle” on global warming, however: nearly half of that group has no more than a high school diploma and less than 25% finished college.

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