Evidence from the paleoclimate data shows that as the Earth cooled down 50 million years ago, CO2 levels were between 1000 and 2000 ppm. Circa 25 million years ago when CO2 ppm fell to ~450 ppm, Antarctica glaciated. It iced over.
It is uncertain when these slow feedbacks kick-in. But carbon dioxide emissions are currently increasing 3% per year. At this rate, we are 30 years from the 450 ppm level that turned Antarctica into a glacier.
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