for National Geographic News
The message in An Inconvenient Truth, the new movie starring former U.S. Vice President Al Gore, is clear: Humans are causing global warming, and the effects are devastating.
Most scientists agree that the Earth is heating up, due primarily to an atmospheric increase in carbon dioxide caused mainly by the burning of fossil fuels such as coal and petroleum.
But how accurate are some of the scientific claims made in the documentary?
In an attemp to clear the air, National Geographic News checked in with Eric Steig, an earth scientist at the University of Washington in Seattle, who saw An Inconvenient Truth at a preview screening.
He says the documentary handles the science well.
"I was looking for errors," he said.
"But nothing much struck me as overblown or wrong."
Claim: According to the film, the number of Category 4 and Category 5 hurricanes has almost doubled in the last year.
"This is true," Steig said. "There is no theoretical basis for the notion that this is a [natural] cycle."
A study published in the journal Nature in August found that hurricanes and typhoons have become more powerful over the past 30 years.
The study also found that these upswings in hurricane strength correlate with a rise in sea-surface temperatures. Ocean heat is the key ingredient for hurricane formation.
SOURCES AND RELATED WEB SITES