Commentary on: Hsiang et al (2017) “Estimating economic damage from climate change in the United States.”
In brief: the authors predict a whole lot of climate-caused misery in the US by the year 2100, given the “business-as-usual” emissions scenario of “Representative Concentration Pathway 8.5” (RCP8.5), the worst-case RCP. Fortunately, as my previously posts in this series have clearly documented, the socio-economic assumptions associated with RCP8.5 are mostly a bunch of hogwash, except for a projected human population of 12 billion by 2100. But population growth alone isn’t enough to give us the global warming hell envisioned by RCP8.5. For that, you’d need to reverse current trends in energy consumption, technology development and agricultural land use.
Hsiang et al also fix the scale and spatial distribution of the US population and economy at 2012 values, meaning the same scale/distribution applies in 2100 ; they explain the analytic burden would become unwieldy otherwise – too much uncertainty, too many moving parts. But human migration is a constant in human history and prehistory. If conditions worsen in some parts of the US, people will leave for greener pastures and better weather. And by moving, they help the regions left behind, e.g., by reducing unemployment. Pretending Americans just stay put for 80 years might make the job of prediction easier, but it’s implausible.
I’m tempted to say “Estimating economic damage from climate change in the United States” is a noble failure, a well-meaning endeavor of questionable value due to a few missteps. But I don’t believe it. What I believe is that the authors deliberately chose implausible worst-case assumptions because the resulting projections of economic damage would be more likely to spur policy action than more plausible middle-of-the-road assumptions. In other words, they let an agenda trump scientific integrity. This is not to comment on the merits of the agenda, which is irrelevant to the merits of the scientific case.
Reference:
“Estimating economic damage from climate change in the United States.” By Solomon Hsiang, Robert Kopp, Amir Jina, James Rising, Michael Delgado, Shashank Mohan, D. J. Rasmussen, Robert Muir-Wood, Paul Wilson, Michael Oppenheimer, Kate Larsen, Trevor Houser Science 30 Jun 2017: 1362-1369.