He's examining plant fossils from the Arctic, and what he finds challenges everything we assume about climate stability. The same location shows alternating layers: arctic climate, then temperate, then arctic again, then temperate. These aren't minor shifts. We're talking about the difference between New York in summer and a landscape where certain arctic plants can't even survive today. The evidence sits right there in the stratigraphy, undeniable.
And here's the scale of it: where we're sitting right now, during the last ice age, this exact spot was buried under nearly a mile of ice. Not a dusting. A mile. The climate doesn't just nudge back and forth on a gentle curve. It swings, dramatically, repeatedly, in ways that rewrite entire ecosystems. That's what the rock record shows us, if we're willing to look.