While the American public has been misinformed by a media obsessed with sensational debate, climate scientists developed a way forward that helps them to compare notes and test one another’s ideas and also creates a valuable communication channel. Called the Intergovernmental Panel on Climate Change, or IPCC, it produces a detailed summary of the state of the science every four years, with the next one due out in February 2007. Although far from perfect, the IPCC involves serious climate scientists from many countries and has largely withstood political attack and influence.

The IPCC reports are fairly candid about what we collectively know and where the uncertainties probably lie.

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In the second category are findings that most climate scientists agree with but are disputed by some:

• The global mean temperature is now greater than at any time in at least the past 500 to 1,000 years.

• Most of the global mean temperature variability is caused by four factors: variability of solar output, major volcanic eruptions, and anthropogenic sulfate aerosols and greenhouse gases.

• The dramatic rise in global mean temperature in the past 30 years is owing primarily to increasing greenhouse-gas concentrations and a leveling off or slight decline in sulfate aerosols.

• Unless measures are taken to reduce greenhouse-gas production, global mean temperature will continue to increase, about 2.5 to 9°F over the next century, depending on uncertainties and how much greenhouse gas is produced.

• As a result of the thermal expansion of sea water and the melting of polar ice caps, sea level will increase six to 16 inches over the next century, though the increase could be larger if large continental ice sheets become unstable.

• Rainfall will continue to become concentrated in increasingly heavy but less frequent events.

• The incidence, intensity, and duration of both floods and drought will increase.

• The intensity of hurricanes will continue to increase, though their frequency may dwindle.