PAOC Colloquium: David Archer (U Chicago)
Title: A few new perspectives on humanity and Earth’s climate
When fossil fuel energy was discovered, the timing and intensity of the resulting climate impacts depended on what the natural CO2 concentration in the atmosphere was at that time, which could have been anything. The radiative forcing scales as the ratio of the fossil fuel CO2 in the atmosphere to the background, natural CO2 concentration. Assuming continued exponential growth in the fossil carbon in the atmosphere, altering the background concentration has the effect of dialing the radiative forcing and climate response back and forth in time. If the natural concentration had been a factor of two or more lower, the climate impacts of fossil fuel CO2 release would have occurred about 50 or more years sooner, making it much more challenging for the developing human society to scientifically understand the phenomenon of anthropogenic climate change in time to prevent it.
Now that we understand the situation, much of our decision-making progress involves money. The costs of cutting CO2 emissions (mitigation) can be balanced against a construct called the Social Cost of Carbon, which is formulated to represent future costs as their present-day equivalents using discounting, in order to compare fairly against the immediate costs of mitigation. U.S. EPA valued the SCC at about $40 / ton of CO2. I will show the derivation of a different but complementary number, the potential Ultimate Social Cost of Carbon to 5000 future human generations of the climate impacts from fossil CO2 release. Long term sea level rise of 50 meters provides the clearest impact. I get about $40k / ton CO2. The formulation treats humanity as any other component of the terrestrial biosphere, in an end-member case where we do not transcend biological limitations such as by soil and water availability. Costs are integrated through time based on the assumption that each generation of humanity values its world (whatever it may look like) equally to any other generation, in particular to our own.