The outline climate bill introduced by senators John Kerry and Barbara Boxer last week is much like the Waxman-Markey cap-and-trade bill passed by the House of Representatives in June. Still, the differences are interesting. This new initiative may in the end do little to spur action on greenhouse-gas emissions in the US. But it is worth noting where the new bill improves on its forerunner, in the hope that its best ideas will stick as the debate grinds on.

The House measure met solid Republican opposition and dissenting votes among conservative Democrats. The arithmetic in the Senate is even less favourable. The prospects for Kerry-Boxer and for any subsequent unified measure, therefore look dim. But the debate is engaged. In the US, ever reluctant to confront climate change seriously, this is progress.