Thus, the challenge of building long term historical GDP data means we should be quite skeptical about turning around and using that data to predict future growth trends. All we’re really doing is extrapolating the backwards estimates of some economists forwards. The error bars will be very large.
Well, Roodman tests for this in his paper, see 5.2, and finds that systematic moderate overestimation or underestimation only changes the expected explosion date by +/- 4 years.
I guess things could change more if the older values are systematically misestimated differently from more recent values? If very old estimates are all underestimates but recent estimates are not, then that could delay the projection further. Also, maybe he should test for more extreme magnitudes of misestimation. But based on the minor extent to which his other tests changed the results, I doubt this one would make much difference either.
But if it’s possible, or even intuitive, that specific institutions fundamentally changed how economic growth occurred in the past, then it may be a mistake to model global productivity as a continuous system dating back thousands of years. In fact, if you took a look at population growth, a data set that is also long-lived and grows at a high rate, the growth rate fundamentally changed over time. Given the magnitude of systemic economic changes of the past few centuries, modeling the global economy as continuous from 10,000 BCE to now may not give us good predictions. The outside view becomes less useful at this distance.
Fair, but at the same time, this undercuts the argument that we should prioritize economic growth as something that will yield social dividends indefinitely into the future. If our society has fundamentally transformed so that marginal economic growth in 1000 BC makes little difference to our lives, then it seems likely that marginal economic growth today will make little difference to our descendants in 2500 AD.
It’s possible that we’ve undergone discontinuous shifts in the past but will not in the future. Just seems unlikely.
Updates to this:
Nordhaus paper argues that we don’t appear to be approaching a singularity. Haven’t read it. Would like to see someone find the crux of the differences with Roodman.
Blog ‘Outside View’ with some counterarguments to my view:
Well, Roodman tests for this in his paper, see 5.2, and finds that systematic moderate overestimation or underestimation only changes the expected explosion date by +/- 4 years.
I guess things could change more if the older values are systematically misestimated differently from more recent values? If very old estimates are all underestimates but recent estimates are not, then that could delay the projection further. Also, maybe he should test for more extreme magnitudes of misestimation. But based on the minor extent to which his other tests changed the results, I doubt this one would make much difference either.
Fair, but at the same time, this undercuts the argument that we should prioritize economic growth as something that will yield social dividends indefinitely into the future. If our society has fundamentally transformed so that marginal economic growth in 1000 BC makes little difference to our lives, then it seems likely that marginal economic growth today will make little difference to our descendants in 2500 AD.
It’s possible that we’ve undergone discontinuous shifts in the past but will not in the future. Just seems unlikely.