Stabenow, whose state is heavily dependent on coal, is rightly concerned about the economic impact of Obama's cap-and-trade plan for reducing carbon dioxide emissions, which will sharply increase the cost of fossil-fuel energy. But she is mistaken if she thinks that "green jobs" can compensate for the economic pain that plan must inflict in order to work.

To see the fallacy here, consider this: If Obama could snap his fingers and make global warming disappear tomorrow, should he do it? By his logic, no, because then we'd lose all those wonderful green jobs that will help pull us out of the recession.

The justification for a cap-and-trade system (or a carbon tax, which likewise aims to shift the economy away from fossil fuels by making them more expensive) lies not in the jobs it will "create," which will be more than balanced by the jobs it will destroy or forestall, but in the bad consequences it will prevent. Obama alluded to those in his speech, saying, "the long-term threat of climate change could result in violent conflict, terrible storms, shrinking coastlines and irreversible catastrophe."

To know whether Obama's cap-and-trade proposal makes sense, we need to know how likely those outcomes are and how costly they would be. We also need to know how likely it is that his plan actually would prevent the dire results of which he warns and, crucially, at what cost.

Critics such as Bjorn Lomborg, author of "Cool It: The Skeptical Environmentalist's Guide to Global Warming," argue that adapting to climate change is much more cost-effective than trying to prevent it, an effort they say is unlikely to have any measurable impact. Presumably Obama thinks these skeptics are wrong. I'd like to hear why.

But that would require the president to be more candid about the sacrifices demanded by his plan to create "the new energy economy." It is difficult to perform a cost-benefit analysis if you refuse to admit there's a cost.