- When the atmosphere's had this much CO2 in the pst, temps have been much warmer, sea levels 70 ft higher (not at equilibrium yet)
- Easy to forget about cycles that affect climate on more astronomic scales— axis tilt swiveling every 20k years or so → flip N & S hemisphere climates
- Earth has much more often been warmer than it is, no ice sheets
- What did that world look like, 50 mya?
- Just as mammals were emerging
- India collided with Asia → CO2 spewing volcanoes quieted, weathering rocks in Himalayas, Indonesia → carbon drawdown
- Now, all this may be undone in mere decades
- Periods of climate instability → ice thawing and freezing → dramatic changes to landscape happening quickly, relatively speaking
- Leap back 129,000 years → temps about 1 degree warmer, but sea levels 20-30 ft higher than now
- Jump back over 3 million years → "the Pliocene, the world of the distant present"
- Last time CO2 was similar to anthropogenic levels
- Temps 3-4 degrees C warmer, sea levels 80 ft higher
- Time of Lucy roaming Earth
- Polar amplification → Arctic regions are 15-20 degrees warmer
- Overall, much wetter world than our predictions— perhaps inadequacies in modelling clouds?
- Usually, once you have a land-based Antarctic ice sheet, feedback loops make it hard to get rid of
- Not the case in Miocine, 16 mya— ice sheet very tuned to CO2 levels
- May be even more sensitive today
- Industrial civilization ≈ supervolcano
- Finally, 50 mya = more extreme than worse-case CO2 conditions in the next 100 years
- No Antarctic ice sheet, polar jungles
- Warmer air holds more water > incredibly humid, far too wet for human physiology
- Violent storms, megafloods, boiling seas and acidic oceans
- Extremity of conditions suggests our models might be missing something— feedback loops that might lead to higher CO2 levels than we expect