What We Know About Climate Change


In a policy article for Science magazine, Jerry Mahlman wrote “...the state of the science of greenhousewarming is often warped in differing ways by people ... with widely varying sociopolitical agendas and biases.” and“...such distortions grossly exaggerate the public’s sense of controversy about the value of the scientific knowledgebase...”. He describes the scientific consensus about greenhouse warming and climate change as a series of facts, virtually certain projections, very probable projections, and probable projections.

Virtually certain facts are that greenhouse gases in our atmosphere are increasing because of human activities and these gases act directly to heat the planet. Virtually certain projections, those that have a greater than 99 out of 100 chance of being true include, stratospheric cooling and more water vapor in the air closer to the planet’s surface. Very probable predictions have a greater than 9 out of 10 chance of being true and include a 1.5 to 4.5 degree Celsius global warming by the year 2100; substantial sea level rise; and an increase in global mean precipitation.

We spoke with Dr. Mahlman about his work as an honest broker in the policy debates about global warming and climate change.

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