Peter Clack@PeterDClack
Planet Earth is 'still' in the Late Cenozoic Ice Age — an unbroken ice-age ecosystem that began roughly 34 million years ago with the glaciation of Antarctica.
Technically speaking, we are living through one of the colder periods in Earth’s geological history. How does that fit into 'global warming'?
For roughly 70–80% of the last half-billion years (the Phanerozoic Eon), Earth has existed in a 'hothouse' state, largely devoid of polar ice sheets but crammed with life. Almost 80% of the Earth was tropical rainforest pole to pole. Temperatures sat between 18°C and 25°C — all well above today's very modest 14°C to 15°C.
Human civilisation developed within the embrace of the Holocene warm interglacial - during an ice age. The primary drivers steering Earth between a deep freeze and warm interglacial over 2.58 million years were not atmospheric — they stemmed from orbital mechanics, specifically Milankovitch cycles (eccentricity, axial tilt, and precession).
While CO₂ forms a feedback loop in paleoclimate records, data shows it is orbital variations that pull the trigger on major ice-age transitions.
The modern climate debate often treats today's baseline of 15°C as an absolute planetary limit, set in stone. Yet it is a momentary snapshot of one fraction of Earth's deep history. Modern human infrastructure and agriculture are clearly optimised for the current climate conditions. But today is just a microsecond in geological or planetary terms.
Treating this fleeting era as the Earth's natural state wipes millions of years of geological reality off the table.
