Earth-system sensitivity in the geological past
- Earth-system sensitivity is >3 oC during times with continental ice sheets and probably >3 oC during ice-free times;
- Both the magnitude of radiative forcing and its rate of change today are highly unusual in a geologic context.
Plant gas-exchange proxy for paleo-CO2
- Advantages: driven by first principles, can be applied to most stomatal-bearing C3 plants, and does not saturate at high CO2;
- Error rate for individual species is ~20%, but is less for multiple species; thus, use multiple species when possible;
- Fossil applications:
- pulse in CO2 associated with end-Cretaceous bolide impact is ~200 ppm; this is smaller than previous estimates and easier to model with carbon cycle models;
- CO2 during the early Paleocene may have been ~500-700 ppm; this is higher than most previous estimates and more compatible with our understanding of warm climates;
- Paired CO2 and temperature estimates for the Arctic during the Eocene suggest more amplification than do model
