What is the relevant uncertainty for climate change policy?

A number of people have climbed onto Twitter and outlined (correctly) how increased uncertainty about the impact of climate change increases the value of doing something about it.  There is downside risk, and of course we wish to buy insurance against that in the form of a more active climate change policy.  Still, that is not looking deeply enough.  I see some of the relevant uncertainties as embodied in the following scenario, which is more about policy means than climate change science:

Following a Trump debacle, finally the Democrats win all branches of government and pass a climate change bill.  There is a carbon tax, and further anti-coal measures, but it isn’t enough to shift energy regimes in a transformational sense (besides, truly transformational technologies require luck and “the right time” far more than price incentives).  Instead the United States becomes more like Western Europe, with higher levels of conservation but no ground-breaking new energy source.  Solar goes up by ten percentage points, and wind by two or three, given NIMBY opposition.  Fracking becomes more efficient yet, which nudges fossil fuels back a bit onto center stage.  Nuclear is closed down altogether, and hydroelectric also goes in reverse or stagnates.  China is as China does, and they slowly move away from their installed coal base, in the meantime taking steps to control their particulate matter but not so much their carbon, copying America in this regard.  India starts a shift from coal to natural gas but still has rising carbon emissions.  Africa and Vietnam exceed growth expectations, with a lot of solar power to be sure, but not enough to counteract their growing industrialization.  The carbon tax causes a mild recession in America, and environmentalism becomes less popular.  The global boost in temperature continues, unchecked.  The people who die each year from regular air pollution — six to seven million at last count — diminish in number with economic growth, but we react largely with indifference to that problem, because it doesn’t fit into domestic political struggles very neatly.

Now, to me something like that is the single most likely scenario, albeit with a lot of uncertainty.  I am still happy to try remedial policy measures, and to try them now, if only out of non-complacency or perhaps just desperation.  But come on, let’s be honest.  If all you are doing is trying to combat uncertainty about the science, you are unwilling to look the actual problem square in the eye, just like the climate deniers, the very people you so much decry.


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