This is true to an extent. I was watching an interesting documentary from a guy who's POV was that there's no global warming but wanted to see if it's in fact a real phenomena.
You are quite right that very recently in earth's history we've seen very cold periods. The last real vestiges of which was "the year without a summer" in 1816. The thing is there was evidence shown to the guy of the earth's climate change over the last 1000 years or so and the trendline was pretty much steady and going up very slowly.
Once the Industrial Age came about and the rise of pollutants such as CO 2 filling the air the trendline made a HUGE leap and climate change has been going at an escalated rate that hasn't been seen to this extent before.
So there IS something definitely going on. I tend to think it's a natural cycle as you've said BUT humanity has pushed it to the limits. In some ways it's akin to giving someone a Red Bull/alcohol mix.

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