Bill Clinton declared last week that Americans "look like a joke" because leading Republican presidential contenders decline to embrace the agenda of the global-warming alarmists. Presumably he had in mind Texas Governor Rick Perry, who says that "global warming has been politicized" and calls claims of a decisive human role in climate change an unproven theory. "You can't win the nomination of a major political party in the US," fumed the former president, "unless you deny science?"

To which Marc Morano, publisher of the irreverently skeptical website Climate Depot, promptly replied: "Bill is correct! No Democratic presidential candidate could get the nomination unless they deny the large role that natural variability plays in climate."

In truth, global-warming alarmism is not science at all -- not in the way that electromagnetic radiation or the laws of planetary motion or molecular biology is science. Catastrophic climate change is an interpretation of certain scientific data, an interpretation based on theories about the causes and effects of growing concentrations of carbon dioxide in the atmosphere. It is not "denying science" to have doubts about the correctness of that interpretation any more than it is "denying economics" to have doubts about the efficacy of Kenyesian pump-priming.

You don't have to look far to see that impeccable scientific standards can go hand-in-hand with skepticism about global warming. Ivar Giaever, a 1973 Nobel laureate in physics, resigned this month as a Fellow of the American Physical Society (APS) to protest the organization's official position that evidence of manmade climate change is "incontrovertible" and cause for alarm.

In an e-mail explaining his resignation, Giaever challenges the view that any scientific assertion is so sacred that it cannot be contested.

"In the APS it is ok to discuss whether the mass of the proton changes over time and how a multi-universe behaves," Giaever writes, incredulous, "but the evidence of global warming is incontrovertible?"