Global warming is a moral issue that society disagrees on. That makes it political .
We want to address global warming because it is the right thing to do. There is no physical law that requires us to do those things. Expecting objectivity on a moral question is just not reasonable. Attacking someones character on the basis of one little flaw in their argument is not going to help. People need to believe in the mission, the specifics of the solution are less important.
It is interesting how much society has tried to depoliticize the environment. Politicians love to setup institutions and legal frameworks that let them shrug-off any responsibility or blame. They don't have to deal with the NIMBYs or campaigners, we have an environmental impact assessment instead. Across lots of different fields you see science used as a crutch to avoid any debate on morality. To make real change we have to address that question head on.