Table: Global Warming: What We Know about It
The White House asked the National Academy of Sciences to identify "the greatest certainties and uncertainties" in the science of climate change. Here are excerpts from the academy's June 6 report:
-- Earth's temperature rose 0.7F to 1.5F during the 20th century
-- Most of the warming stems from a rise in concentrations of greenhouse gases, including carbon dioxide
-- Before the Industrial Revolution, atmospheric carbon dioxide levels were typically 190 to 280 parts per million by volume (ppmv). By 1958, they were 315 ppmv. They are now about 370 ppmv and rising 1.5 ppmv per year.
-- Human activities are responsible for the increase. The primary causes are burning oil, gas, and coal.
-- Computerized predictions of climatic change suggest that the earth's temperature will rise a further 2.5F to 10.4F by 2100. The consequences would include shrinking glaciers, disrupted agriculture, flooded coastal regions, and the increasing likelihood of droughts.