Yes you are correct that the climate has changed plenty of times in the past. The question is: How do you know that? Let me answer for you: Some dedicated researchers figured it out for you, told you, and you believed them. As you should, since they know what they're talking about.
Do you realize how much overlap there is between the people saying the thing you automatically believe, and the people saying the thing you automatically don't?
Fuck "common knowledge". Climatologists sure as fuck are aware that the climate has changed before without human intervention. Yet they have ample reason (as in evidence) to suggest this change is different, and those reasons even take into account previous change. Maybe you should tell one of them how the Sahara was a savannah, and therefore anthropogenic global climate change isn't occurring, because that's such a good argument!
So yeah. You won a fight against an imaginary layman less educated than yourself. Congratulations. Of course your implied counter-logic of "climate change happened before, therefore this time isn't our fault" is equally flawed.
If you get rid of the "common knowledge" aspect of your post, you're basically saying "Scientists say X which is true, and that obviously means the scientists who say Y are wrong." Except the scientists who say X don't agree with that conclusion. I wonder why? Oh yes, because it's bullshit. Your knowledge is no better than that of the strawman you burned.