1. It's not (known to be) happening.
2. If it's happening, humans aren't (known to be) causing it.
3. It's nothing to worry about anyway.
4. There's nothing much to be done about it.
Points 1 and 2 are flatly wrong. Point 3 is weak. Point 4 becomes increasingly true, as time passes and nothing much is done, which is a tragedy.
There's little point discussing Points 3 and 4 with people who wrongly persist in Points 1 and 2. In the current presidential race, there have been two presidential candidates, Romney and Huntsman, who have acknowledged that it's happening and humans are causing it; Romney had said humans are causing the warming, but later that he didn't know how much of it is caused by humans. Now he's converted to this:
“My view is that we don’t know what’s causing climate change on this planet.”The good news is, his opinion is clearly not frozen.
