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Snapshot of Climate Change Science

November 29, 1997

A snapshot of climate change science:

WHAT’S KNOWN

_In the atmosphere, carbon dioxide and other ``greenhouse″ gases, mostly produced by burning coal, oil and gas, allow sunlight through but retain infrared radiation Earth emits back toward space.

_Since the Industrial Revolution began, carbon dioxide concentration in the atmosphere has risen from 280 parts per million to 358.

_Since the late 1800s, mean global temperature has risen between 0.3 degrees and 0.6 degrees Celsius (one-half and 1 degree Fahrenheit). Oceans, which expand when warmed, rose up to 10 inches.

_Computer models project further temperature increases of between 1 and 3.5 degrees Celsius (2 to 6 degrees Fahrenheit) by 2100, possibly the most abrupt climate change in thousands of years.

WHAT’S UNCERTAIN

_The precise ratio of past warming attributable to man-made emissions and natural causes.

_The precise magnitude of warming that will result from given levels of atmospheric gases.

_The role clouds and oceans may play in mitigating _ or aggravating _ warming.

_Future population and economic growth, which affect emission levels.

_Future technological and lifestyle changes that may affect emissions.