Comment on 'Climate sensitivity, agricultural productivity and the social cost of carbon in FUND'.

Dayaratna et al. (Environ Econ Policy Stud 22:433–448, 2020) proposes several improvements to economic- and climate-simulating IAMs and to their input variables. They show that an empirically based ECS estimate, agricultural damage estimates from recent literature, and discount rates as low as 2.5%, when used within the FUND model, yield a negative social cost of carbon through mid-twenty-first century. Five of their propositions, that "fat-tails" of the ECS distribution are improperly simulated by IAMS, FUND does not simulate enough benefits for agriculture, the ECS is near 1.5 °C, DICE and PAGE overestimate the SCC, and the marginal cost of public funds for carbon taxes has a value of at least a few dollars, are more closely analyzed. Estimates of ECS from a recent paper and a 5% discount rate applied to FUND result in an SCC estimated to lie within the range of about −$1 to $2.50 per metric ton CO2 for the year 2020. [ABSTRACT FROM AUTHOR]