Are you listening to the number 350, Mr. President?

Millions of people want you to.

Yes, the exact number, of limiting carbon-dioxide concentrations in the atmosphere to 350 parts per million, may be unrealistic.

Robert J. Brulle, a sociologist at Drexel University who analyzes environmental campaigns, expressed a mixed view of the 350 campaign. It represents “a new wave of civic environmentalism” that has proved vital to solving problems, he said, but that approach was abandoned long ago by many big environmental groups that now focus mainly on legislation and litigation.

But, if we don't set a hard number, draw a line somewhere,, people like U.S. President Barack Obama, or the Chinese or Indians, will feel even less compelled to act.

And, contra Brulle, litigation doesn't work on trans-national problems. Legislation is glacial here in the U.S., without the president prodding.