Kan klimaskeptikere ha noe på fare med, spør Christian Science Monitor, og finner to moderate utgaver. Svaret på spørsmålet later til å være nei. Men kanskje leverer de noen skeptiske spørsmål det kan være greit å ha bak øret.
Mr. Taylor manages the Oregon Climate Service, and much of his work has to do with global warming. «I’m certainly in favor of doing prudent things to reduce the human impact,» he says.
But unlike most climate scientists, he does not believe that anthropogenic (human-caused) greenhouse gases – mainly from coal-fired power plants and motor vehicles spewing carbon dioxide – are the main culprits. In fact, he says, «It’s my belief that in the last 100 years or so natural variations have played a bigger role.»
Among the forces of nature he cites are changes in solar radiation, «very significant influences» of the tropical Pacific (El Niño and La Niña events in decades-long cycles), as well as changes in Earth’s tilt and orbit over cycles lasting thousands of years.
Above all, says Mr. Taylor, who is past president of the American Association of State Climatologists, «The climate system is very, very complex, and the more we learn, the more we see that we really don’t understand it.»
Meyer’s engineering background is in feedback and control theory, so he especially takes issue with the belief among many climate scientists (as well as activists such as former Vice President Al Gore) that what had been a long-term, stable climate system is now dominated by «positive feedback .» Positive feedback means that as temperatures rise in extraordinary fashion there will be a tendency for global warming to speed up. One example is when light-colored sea ice melts to reveal darker ocean water, which in turn absorbs more heat, which melts more ice.
Meyer contends that in physics (and in nature) the tendency is just the opposite: a «negative feedback» will occur as CO2 levels rise – in other words, cooling mechanisms will set in. In the case of carbon dioxide and global temperature, «future CO2 has less impact on temperature than past CO2,» he says.
One bit of recent research may give some weight to Meyer’s argument.
Researchers at the University of Alabama’s Earth System Science Center in Huntsville studied heat-trapping tropical clouds thought to result from global warming. They found an apparent decrease in such clouds as the atmosphere warms, allowing more infrared heat to escape from the atmosphere. The cloud decrease appears to be «negative feedback,» meaning that as warming continues it sets off another process that counters its effects.
Men Taylors syn vinner ikke oppslutning hos etablerte forskere. De peker på oppvarmingen av havene som bevis på at det er menneskelig aktivitet som har skylden.
«For me, the most compelling single data set that undermines that suggestion is the increase in the heat content of the oceans,» says Daniel Lashof, science director for the climate center at the Natural Resources Defense Council in Washington, an environmental lobbying group.
Another environmental group, the Union of Concerned Scientists, notes that higher temperatures have been found 1,500 feet deep in the ocean. It calls ocean warming the No. 1 «human fingerprint … well outside the bounds of natural climate variation.»
«There’s just no argument about it,» Dr. Lashof says. Heat «is going down hundreds of feet … an accumulation of heat that there’s just no other explanation for other than that the earth has been driven out of energy balance with the sun by this accumulation of heat-trapping gases in the atmosphere.»
In a recent report, Wang and colleague Bill Chameides, chief scientist at Environmental Defense, write:
«Independent measurements demonstrate that the increased CO2 in the atmosphere comes from burning fossil fuels and forests. The isotopic composition of carbon from these sources contains a unique ‘fingerprint.’ The only quantitative and internally consistent explanation for the recent global warming includes the intensified greenhouse effect caused by the increase in CO2 and other greenhouse gases.»