Of course. And the evidence shows that global warming is happening, and that human activity is responsible.
Partly responsible. Otherwise, I agree. So what? My argument hasn't been that AGW doesn't exist, but that there isn't compelling reason to act on it in a costly way.
We do. But how much do we value a pacific island nation that would disappear because of climate change? I mean not only the land but its people and culture. How much do we value species that would go extinct? That's not an answer for economists, it's a moral/political one. You can't answer that with science. Therefore you will never have scientific evidence that we should invest X$ to fight climate change, just like you will never have scientific evidence of the opposite. And this is not a valid reason for not doing anything.
What's your willingness to pay out of your own wealth to protect these things? That tells me exactly how valuable these things are. And that's how you transform any preference into a purely economic question.
So the best we have are reports such as the Stern, Garnaut, and IPCC reports. They all conclude we should lower our emissions.
Here's a propaganda lesson for you. These are first past the post arguments from authority. Just because they existed before most counterarguments were formulated. doesn't mean that they were the best arguments even at the time of their creation. For example, the Stern report's flawed time value factor was readily apparent, meaning that reinterpreting the study through a more appropriate time value is already at the time of the publishing of the Stern report, is already better than the Stern report was.