A John Nichols article in The Nation is teased on the home page thusly:

Is the Bush Administration's deliberate inaction and delusional denial of global warming an impeachable offense? John Nichols reports on the Green Party's efforts to call the President to account.

The answer is no, it is not.

Indeed, this is part of the problem with impeachment as it's set up. If you could prove that Bush had taken a $5,000 bribe in order to appoint someone's son ambassador to Portugal, that would be impeachable offense even though it also wouldn't be a big deal in the scheme of things. Conversely, the Bush administration's stance on climate change is incredibly harmful, and quite corrupt in its own way, but by no means impeachable.