So... Hillary Clinton released her climate and energy plan, which can be read in full here. The broad outlines are just as audacious as what Edwards and Obama have proposed: She'd aim to curb U.S. greenhouse gas emissions 80 percent from 1990 levels by 2050—a goal urged by a growing number of scientists and green groups—through a cap-and-trade regime, with the pollution permits auctioned off rather than given away for free. That last bit is a key design point (see here for a handy explanation), and would help avoid some of the problems plaguing Europe's emissions-trading system. A good step all around.

You know, looking this thing over, it's hard to agree with folks like Ted Nordhaus and William Shellenberger that environmentalists have lost their way in recent years. After all, a few years back, an 80 percent reduction in greenhouse gases and 100 percent auction of pollution permits was considered a fringe position on energy policy. Now all of the leading Democratic presidential candidates are advocating just that. It's a seismic shift by any measure.

P.S.: Okay, one criticism: It'd be nice if this plan included stronger measures to ease the burden on low-income households (along the lines of what Obama has proposed). As Robert Greenstein recently told Congress, even a modest reduction in emissions could, potentially, raise energy bills for the bottom 20 percent of households by $750-$950 a year. The sort of home-efficiency and weatherization programs Clinton is proposing would help mitigate that, but those take time to implement. Alternatively, argues Greenstein, with just 15 percent of the revenue generated by auctioning off pollution permits, policymakers could offset the higher energy costs for low- and middle-income Americans through tax credits or rebates—and still have plenty of money left over to fund public transportation, R&D, and whatnot.