Wisdom of the experts: Using survey responses to address positive and normative uncertainties in climate-economic models

The social cost of carbon (SCC) and the climate-economic models underlying this prominent US climate policy instrument are heavily affected by modeler opinion and therefore may not reflect the views of most climate economists. To test whether differences exist, we recalibrate key uncertain model parameters using formal expert elicitation: a multi-question online survey of individuals who have published scholarship on the economics of climate change, with 165 to 216 respondents, depending on the question. Survey questions on the magnitude of climate impacts and appropriate discount rates revealed that prevailing views differ from prominent IAMs, including DICE. We calibrate the DICE damage functions and discount rates to reflect the mean and median survey responses, respectively, recognizing these two parameters’ differing sources of uncertainty (positive versus normative). We find a 16-fold higher SCC than the base DICE-2013R assumptions, with a range of 11- to 24-fold under alternative modeling assumptions (using the DICE-2016R2 model version and calibrating damages to median rather than mean responses). Our findings support a 7- to 13-fold SCC increase for different respondent subgroups even when we exclude the potential for catastrophic climate impact shocks. Our results reveal a significant disparity between IAMs and the broader community of scholars publishing in this field.