Global-warming skeptics: Might warming be 'normal'?

Some say that today's climate change is merely part of a natural cycle.

from the September 20, 2007 edition

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Is climate 'feedback' positive or not?

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.

Neither Taylor nor Meyer (nor most other climate change skeptics, some of whom call themselves "global-warming optimists") deny that modern human development in the form of additional greenhouse gases has played a role in warming the planet.

But most of them agree with Meyer when he says, "To this day, there's still no empirical proof of how much warming is coming from CO2. There's a lot going on, and it's almost impossible to pick effects out."

Warming oceans tell a different tale

That flies in the face of what most scientists say. "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."

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