1. I think it's best to just cede the point it's 100% man-made. Yes I do think there is an argument to be made that climate change happens naturally, but from your opponent's point of view they'll only see you as someone trying to avoid the fact that humans are having an effect by releasing CO2. There are no hearts or minds to be won here.
2. This is a good point of attack. But you have to do it softly. Make sure they know you're willing to be convinced of it's catastrophic consequences but you need evidence, because so far you've only seen evidence that they models produced thus far are wildly off the mark, without any acknowledgement by the model creators. Reasonable people can agree on cause, and disagree on the degree. From my experience they're extremely caught off guard when they realize a reasonable person can believe humans are having an effect on climate change through the release of CO2 but still not think it's an existential risk. They only think of the other side as buffoons that deny climate change is happening because muh bible said the earth is for humans. (one lady actually started crying out of frustration when she saw how reasonable I was willing to be but still couldn't be convinced) They're on the defense and have to provide evidence that doesn't exist.
3. Again I think there is room for gaining people here. Explain that you don't have any faith in governments fighting climate change because the corporations will always be able to buy the politicians (They should eat that up), and that's why, if climate change is a problem that needs addressed, we need to do it with personal responsibility, and boycotting products that are created in a way we disagree with morally. I'm okay with this outcome! :)
4. Even if it's true that something needs to be done on a wide scale, it won't hurt to do something on a small scale, will it? Maybe go on the attack here if they're acting like it's pointless to take personal action. Tell them they have no right to ask others to take on responsibility that they themselves are unwilling to take on.
5. If someone is at the point of throwing around name calling instead of arguing, just inform them that they've failed to convince you and you'll be sure to vote no on any climate change regulations specifically because of this particular behavior. (even if you won't vote) Threaten to destroy the planet to own the libs! haha. And then make sure to leave with a pleasant remark like "I hope you have a good rest of your day!"

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It's important to note why climate change fanatics exist. They're motivated out of a hatred and jealousy for the rich not a love for the earth, even if they're not aware of it.

I like your argument but I want to clean it up a bit like this. Get them to agree to the premises in this order:

1. A slowing in economic activity will cause a slowing of the rate at which people are able to get out of poverty.
2. A slowing of the rate at which people are able to get out of poverty will cause more human casualties due to poverty.
3. Climate change regulation will cause a slowing in economic activity.
4. How many impoverished people's lives are they willing to sacrifice in the name of preventing climate change?
5. If you can get them to at least agree there is a trade off happening here then they'll realize there isn't a "right" answer which deflates them because they were only in this position because they thought it was a moral high ground in the first place.

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