SEN. BOB Smith, sometimes a Republican, became chairman of the Senate's environmental committee on Tuesday. This is a bit troubling: The League of Conservation Voters reckons only 36 percent of his Senate votes were friendly to the environment; the previous chairman, the late John Chafee, scored 70 percent. But Mr. Smith's past is not necessarily a guide to his future. Back in July, he stormed out of the Republican Party, accusing it of putting pollsters before principles. This week he rejoined the party, lured by a committee chairmanship.

His elevation coincides with an environmental summit in Germany, at which the signatories to the Kyoto treaty on global warming are working out a schedule for reducing carbon emissions. The schedule is worth less than it might be, because America is unlikely to participate fully until the Senate ratifies the Kyoto treaty. Ratification eluded even the estimable Mr. Chafee. But there is a milder kind of progress that a wise chairman would support.

In a bill introduced last March, Mr. Chafee and two colleagues offered companies that take steps to reduce emissions voluntarily credit for such early actions if Kyoto-style regulations eventually become law. If, for example, a firm freely chooses to reduce emissions by 10 percent between 2000 and 2005, a law passed in 2005 mandating 10 percent reductions will impose no further burden on it. A law mandating 20 percent reductions would oblige the firm to cut emissions by a further 10 percent. A law mandating 5 percent reductions would leave the firm with a credit that could be sold to other polluters.

The Chafee bill would not force firms to do anything; it is therefore hard to understand how business supporters can object. But it would remove the current disincentive to voluntary cuts in emissions. At present, firms have to think twice: If they make the easy reductions now they may be left with only hard options later. Some companies, led by DuPont, have promised to slash emissions anyway. But more might follow if Mr. Smith honored the memory of his predecessor by taking up his bill.