English: Today’s CO2 is roughly 120 ppm higher than the highest levels humans have survived long-term. Nature has removed similar massive amounts of CO2 preceding ice ages, ten times in the last 800,000 years. The CO2 that reduces levels by 120 ppm is mostly converted to biocarbon by phytoplankton and stored in the deep ocean, and released when the ice-age ends. The phytoplankton growth corresponds with ocean iron concentration.