Garg, I like you and for the most part I find myself usually in agreement with you.
My observation for what it's worth:
I think you have created a straw-man to lay a beating on, if I may, your premise #3 is inaccurate.
Do scientists continue to tell us that mankind is 100% responsible for climate change? Answer = YES
No, actually, I have never once heard anybody with a scientific background ever state this once. I would ask you to provide citations for this observation.
A 'logical argument' in order to be true must rely on the premises all being correct, since your premise #3 is incorrect your argument if there is one....is invalid.
Humans certainly do affect climate change but to what degree is the question. In fact, there are lines of reason and thought that show that if not for humans burning stuff starting a few maybe 10s of thousands of years ago that we would be in an ice age. Human climate change saved the world but sooner or later it might be too much. I certainly can see evidence of climate change, it was only a few 10s of thousands of years ago when there were miles of ice right where I live now. We can see the scrape marks left in bedrock from the miles of ice pushing down on boulders locked in in ice that were dragged across the bedrock as the glaciers advanced. Well technically the glacier can be 'in retreat' and yet still have the ice move forward.