Global Warming Becomes Major US Campaign Issue(1/3)

The U.S. National Academy of Sciences says there is a growing body of evidence that the Earth's atmosphere is warming and in recent decades that temperature change has been caused by human activities.

Scientists at the Academy say the most striking proof of global warming is what they call a relatively rapid and widespread increase in temperature during the past century.
They say other evidence of warming, such as increases in ocean temperatures, shrinking mountain glaciers and the decreasing polar ice cover are consistent with this trend.

David Sandalow, an energy and environment scholar at the Brookings Institution, says the evidence is clear.

"We have a good body of science on the impacts of global warming, we have never seen greenhouse gas concentrations in this range in all of human history. They are accelerating at rates that are wildly unknown in human history. The potential threat is very serious."

The National Academy of Sciences says greenhouse gases have increased significantly since the Industrial Revolution, mostly from the burning of fossil fuels for energy, industry and transportation.

It was only in recent years, however, that most scientists and political leaders began to agree that the changes are due primarily to human behavior.