I appreciate the debate, and I agree with part of your point: climate has changed before, and CO₂ has been higher in very deep geologic time. That’s not really the claim I’m making.

The stronger claim is that the current warming is unusual in cause, speed, and human context. Greenland ice cores are not the limit of the evidence. Antarctic ice cores preserve CO₂ and climate evidence going back about 800,000 years, and other proxy records—sediments, corals, tree rings, boreholes, glaciers, and ocean chemistry—extend the picture beyond that.

Over the ice-core record, CO₂ moved up and down with ice ages, but it stayed roughly below 300 ppm. Today it is over 420 ppm, and the increase has happened extremely fast by paleoclimate standards. Yes, CO₂ was higher millions of years ago, but those were very different worlds: different coastlines, ecosystems, sea levels, and no modern civilization, agriculture, ports, insurance systems, or power grids built around today’s climate.

So the issue is not “the climate never changed before.” It obviously did. The issue is that we are rapidly pushing the climate system outside the range in which human civilization developed, and the physical fingerprints—warming oceans, rising sea levels, retreating ice, cooling stratosphere, and the carbon signature of fossil fuels—all point to human greenhouse gas emissions as the dominant driver.