Clinton is catching up to Edwards and Obama with a comprehensive plan on climate change. Link goes to what appears to be a white paper by Clinton reproduced at Grist, although I can't find the same document anywhere on Clinton's website. It's a non-trivial issue, because this document is the only place committing to short term carbon caps - "A fundamental cornerstone of Hillary's plan is reducing greenhouse gas emissions to 1990 levels by 2020" - which I think may be more important than the commitment politicians would have of our grandchildren in the year 2050.
General opinion seems to be that her plan's not substantially better or worse than Edwards' or Obama's. I dunno - Obama's campaign says he "will start reducing emissions immediately in his administration by establishing strong annual reduction targets" to meet the same 2020 goal as Clinton. Immediate reductions sounds comparable to Edward's cap on emissions in 2010, but Clinton doesn't mention an immediate goal. I hope she doesn't expect the emissions reductions to start in 2017, after she leaves office.
UPDATE: Here's her plan on her website, with the 2020 quote.