“Aha! We knew it!” a number of conservative columnists have been crowing lately. “Greenhouse, schmeenhouse, go right on driving those sports utility vehicles.”

The cause of their excitement is an article published in Science magazine, one of the most prestigious places a scientific article can be published, claiming that the North American continent is a huge carbon sink. The authors found, essentially, that the carbon dioxide content of air blowing onto our west coast is higher than that of air blowing out to sea from our east coast. (Carbon dioxide is the primary greenhouse gas.)

Somehow, the authors conclude, in crossing the continent, the prevailing westerlies must run across massive carbon dioxide absorbers, perhaps growing forests. Those forests, or whatever, must take even up more carbon dioxide than the enormous amount we put out as we burn coal, oil, and gas. (North America accounts for 25 percent of the world’s fossil fuel consumption with just six percent of the world’s people). Therefore, say the columnists, not the scientists, we are not causing any greenhouse warming and needn’t be bothered with the Kyoto climate treaty.

“I don’t believe that article,” said a visiting forest scientist at a Dartmouth seminar this week. “I don’t know anyone who believes it.”

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So goes science, back and forth, up and down, maybe, maybe not, that’s an interesting finding but let’s see if we can repeat the experiment, let’s see if there are other explanations, let’s put it in the perspective of all these other findings.

And so goes column-writing, a handmaiden of politics, which likes to seize any shred of evidence to support what one already thought and hit everyone over the head with it. A difficult combination, science and politics. Especially in a democratic society where the public is charged with figuring out what to believe.

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Take the dioxin muddle, for example. This chemical (set of chemicals, actually) is a common contaminant in some herbicides, in wastewater from paper-making, in the stack gas of garbage incinerators. Science found it to be poisonous early on; environmentalists hyped it into “one of the most toxic chemicals known to humankind.” Then the chlorine industry did some studies that found it to be not so immediately toxic after all, and the conservative columnists proclaimed it harmless.

Along came new science about chemicals that act like hormones and disrupt the development of embryos. They’re called endocrine disrupters. Dioxin proves to be one of the most powerful. Excruciatingly tiny amounts seem to distort all sorts of developing critters: birds, fish, reptiles, mammals, people too.

Now both the pro- and anti-dioxin crowds have evidence they can blow out of proportion. So is dioxin safe? Science is still figuring it out. In the meantime, how much risk do we want to run with developing critters?

Another study on endocrine disrupters, from a respected lab, seemed to confirm something environmentalists had suspected for a long time. Several different chemicals apparently acted together to create thousands of times more disruption than any one of them alone.

That result hit the press hard, one set of true believers trumpeting it, the other set studiously ignoring it.

Meanwhile other labs tried to duplicate the study and couldn’t. Soon the original researchers published a retraction; they couldn’t repeat the results either. That happens sometimes. These are delicate processes. There could have been a contaminant in the solutions or even in the plastic labware. Exactly that problem has messed up endocrine disruption studies before. The researchers would be considered dishonorable only for failing to publish a retraction, not for publishing one. That’s science.

Politics, on the other hand, is writing nyah-nyah columns saying, see there? All those fears about exposure to multiple chemicals are groundless. Such columns were, of course, written.

Failure to disprove is not proof. It only means that a particular test showed no effect. In this case the test was in a lab using cultured cells, not in a developing embryo. Both theories — chemicals acting together can add up to worse effects than they do separately, or they cannot — are still alive.

A similar story caused havoc in England last fall. A scientist, again a respectable one from a good lab, found that rats fed genetically engineered potatoes had suppressed immune systems and stunted growth, compared to rats fed ordinary potatoes or even rats fed ordinary potatoes spiked with the specific protein whose code had been spliced into the transgenic potatoes.

That last bit looks scientifically suspicious. So does the fact that the researcher announced his results on TV instead of in a scientific journal. He was fired and forbidden to talk to the press. He sent his data to other scientists, 21 of whom have defended him and asked that he be reinstated. Foes of genetic engineering are demanding to know why his study was suppressed.

So are gene-spliced potatoes dangerous to eat? No one really knows. My scientific instinct says no. Science will slowly find out. In the meantime I’m not inclined to eat them.

Is there a great North American carbon sink? No one really knows. My scientific instinct says no. Science will slowly find out. In the meantime I see no reason to risk the climate of the planet just to drive around in oversized vehicles.