Sixty-three percent of Americans believe that global warming is happening, but many do not understand why, according to a national study released Thursday by Yale University researchers.

The report titled "Americans' Knowledge of Climate Change" found that only 57 percent know what the greenhouse effect is, only 45 percent of Americans understand that carbon dioxide traps heat from the Earth's surface, and just 50 percent understand that global warming is caused mostly by human activities. Large majorities incorrectly think that the hole in the ozone layer and aerosol spray cans cause global warming. Meanwhile, 75 percent of Americans have never heard of the related problems of ocean acidification or coral bleaching.

However, many Americans do understand that emissions from cars and trucks and the burning of fossil fuels contribute to global warming and that a transition to renewable energy sources is an important solution.

Americans also recognize their own limited understanding. Only one in 10 say that they are "very well-informed" about climate change, and 75 percent say they would like to know more about the issue. Likewise, 75 percent say that schools should teach children about climate change and 68 percent would welcome a national program to teach Americans more about the issue.

"This study demonstrates that Americans need to learn more about the causes, impacts and potential solutions to global warming," said study director Anthony Leiserowitz of Yale University. "But it also shows that Americans want to learn more about climate change in order to make up their minds and take action."