Carbon Dioxide At “Highest Level In 400,000 Years”

Global warming is caused primarily by humans and "nearly all climate scientists today" agree with that viewpoint, the new head of the National Academy of Sciences — a climate scientist himself — said Wednesday.
Ralph Cicerone's views contrasted with Bush administration officials' emphasis on uncertainty about how much carbon dioxide and other industrial gases warm the atmosphere like a greenhouse.
"Carbon dioxide in the atmosphere is now at its highest level in 400,000 years and it continues to rise," said Cicerone, an atmospheric scientist who left as chancellor of University of California-Irvine to become academy president this month. "Nearly all climate scientists today believe that much of Earth's current warming has been caused by increases in the amount of greenhouse gases in the atmosphere, mostly from the burning of fuels."