Last week's move across the Capitol by now-Sen. Ed Markey (D-Mass.) fueled a bruising battle to replace him as ranking member of the House Natural Resources Committee. But the more significant opening that he has left may be the role that he filled for more than three decades as one of the House Democrats' chief players on environmental policy. Markey's departure has cast a spotlight on the growing number of ambitious junior House Democrats, who have brought extensive background in dealing with climate policy before they entered Congress and a desire to spur significant action. Although Rep. Henry Waxman (D-Calif.) remains very much a presence as ranking member of the Energy and Commerce Committee, he now has a large corps of partners and prospective successors in an epic generational change.