Climate change has devolved into an ideological litmus test for the Republican Party; if you agree with the science, you're out. But that wasn't always the case. Nay, there was a time, just a short while ago, when a Republican could openly discuss climate change without getting booed and chased from the rafters. But an ideological orthodoxy set in – originating from the goadings of the fossil fuel companies and its think tanks, and championed by Fox News and the conservative punditry – that climate change was a hoax.
And hoaxes don't need addressing. Hoaxes don't demand pollution restrictions or efficiency requirements or preference for cleaner sources of energy.
So that's what you're seeing here: Politicians who clearly understood the scientific consensus view of climate change but did not yet understand the political damage of saying so in public. So, early campaign-era Mitt (as in, Mitt from 6 months ago) could innocently say he believed in climate change. But not current-era Mitt, who must meet the standards of the new orthodoxy. That's why these vids, put together by the Sierra Club are so striking – they highlight the direct impact the Tea Party-influenced conservative establishment has had on the rational urgings these candidates once exhibited.