Very little. A plethora of integrated assessment models (IAMs) have been constructed and used to estimate the social cost of carbon (SCC) and evaluate alternative abatement policies. These models have crucial flaws that make them close to useless as tools for policy analysis: certain inputs (e.g., the discount rate) are arbitrary, but have huge effects on the SCC estimates the models produce; the models’ descriptions of the impact of climate change are completely ad hoc, with no theoretical or empirical foundation; and the models can tell us nothing about the most important driver of the SCC, the possibility of a catastrophic climate outcome. IAM-based analyses of climate policy create a perception of knowledge and precision, but that perception is illusory and misleading.
The paper is worth a read, despite being technical at times. There is a good write-up in the Washington Post by Robert J Samuelson. He says:
Pindyck sounds like a “global warming denier.” He isn’t. True, he thinks climate change and its adverse economic consequences could be wildly overstated. He also thinks they could be wildly understated. The effects might ultimately be catastrophic. We simply don’t know. Ignorance reigns. The best course, he says, would be to adopt a modest carbon tax — because there are certainly some ill effects of global warming — and adjust it as we learn more. Meanwhile, we shouldn’t assume that computer models convey scientific truth. “The models create an illusion of knowledge,” he says. “For me, the issue is being honest.”
The tent of climate pragmatism is getting bigger.
h/t Roger Pielke Jr