Freedom of speech and freedom of the press are bulwarks of American society. Science, however, does not accept any opinion or ideology.

Science honors another principle: respect for evidence. That additional criterion can provide a challenge to newspapers hoping to serve their community on scientific issues, as reflected in a recent editorial notice on publishing claims about climate change (Readers Write, editor's note, Jan. 31).

If climate science were a matter of opinion, there would be no problem. Indeed, many critics seek to gain leverage by framing science just that way: as mere opinion. By calling a scientific claim "progressive," for example, they imply that it is inherently political. Indeed, that rhetoric is perhaps the easiest tactic for discounting the social import of hard-won scientific knowledge.

By sowing doubt, it seems, you can effectively postpone any public action based on scientific analysis. We have already seen it in the cases of secondhand smoke, ozone depletion, acid rain, lead and beryllium poisoning, and pesticides (see the books "Merchants of Doubt" and "Doubt is Their Product," or the website defendingscience.org). Now the target is global warming.

A "view" differs significantly from a "view necessarily informed by evidence." The problem with many climate-change naysayers is that they present their views as facts where they are not accountable to the evidence. They avoid having to address expert review. They dodge the systematic technical criticism that is essential to establishing scientific claims as trustworthy.

In this case, they have failed to persuade the scientific community. Instead, they appeal directly to nonexpert citizens with shards of evidence or emotional pleas, trying to short-circuit the process of validation.

I am not an expert on climate change. But I do know who is. The independent National Academy of Sciences along with the Intergovernmental Panel on Climate Change have long expressed a scientific consensus that past climate change is undeniable and future climate change inevitable. Any individual can repudiate a scientific claim, or the evidence and the consensus of the credible experts behind it. But the consensus remains. Claims that try to upstage that are pseudoscience. They should not be admitted in a public forum where they pretend to have scientific merit. The benchmark of expert scientific consensus matters for collective decisionmaking. There is still ample opportunity to disagree about what to do next.

Many journalists uphold and vigorously defend certain standards of reporting. They expect concrete evidence before publishing controversial claims. They ensure that testimony comes from credible witnesses and experts. They may certify sources to know that they speak authoritatively. They certainly strive to not publish opinion as fact. Ultimately, they limit what is published in heeding their responsibility to be public sources of reliable information.

Those standards matter, too, in broadcasting or printing scientific claims, whether as news or in discussions of public issues. A daily newspaper is not an appropriate forum for debating scientific claims or evidence. The standard of discourse must be scientific consensus when it exists.

Freedom of expression is not an excuse for honoring voices that deny scientific consensus. Media that disregard that standard make a mockery of science and of responsible public discourse.

Douglas Allchin is a fellow at the Minnesota Center for Philosophy of Science at the University of Minnesota.