Risk, Uncertainty and Irreversibility, Decision Theory, and Global Warming

Alex Tabarrok protests that you should not do expensive and irreversible things before you know what is going on. I think that there is an important distinction to be drawn in decision theory between (a) risk on the one hand, and (b) the interaction of uncertainty and irreversibility on the other.

In general, briefly: As a baseline, you should start out thinking that you should do what it would be best to do if your central-case forecast were to come true. And then:

1. Relative to that baseline, you should do more of things that reduce risks: a prudent portfolio should have some gold or silver in it (not much!) to guard against the potential inflationary collapse of fiat money systems and other political risks.
2. Relative to that baseline, you should do less of things that increase risk: invest less in risky enterprises, and dump less carbon dioxide and methane into the atmosphere.
3. You should delay doing expensive and irreversible things until you are confident that they are needed.
4. You should prevent processes that could cause irreversible or incredibly-expensive-to-repair damage until you are confident that their effects will be harmless.

The first two principles are the appropriate ones for dealing with risk. The last two principles are appropriate for dealing with the interaction of uncertainty and irreversibility.

Thus if congress were on the verge of banning open-carbon-cycle power generation and vehicle operation in 2010, I would think that that was a bad idea because of principle 3. But congress isn't. The uttermost limit of political feasibility over the next decade is a fifty-cents-a-gallon-equivalent tax on carbon emissions. And that seems well-covered by principle 2.

Here's Alex:

Marginal Revolution: Uncertainty is the Friend of Delay: Regarding global warming and what to do about it, Brad DeLong approvingly paraphrases Tyler, "uncertainty is not the friend of doing nothing." Bearing in mind the obvious dangers of contradicting both Brad and Tyler let me counter with "uncertainty is the friend of delay."... Suppose... that we are uncertain... there is a strong argument for delay. The argument comes from option pricing theory applied to real options. A potential decision is like an option, making the decision is like exercising the option. Uncertainty raises the value of any option which means that the more uncertainty the more we should hold on to the option, i.e. not exercise or delay our decision....

Applying the theory to global warming isn't easy because our decisions involve many options and exit costs; but if we think that our knowledge of the extent, cost, cause and solutions to global warming are increasing at a faster rate than the danger of global warming then delay of any major decision is a rational policy at the present time.

And Tyler Cowen rebuts:

I see the difference between us as such: you write: "making the decision is like exercising the option...". But many costly decisions increase option value. Such decisions include more R&D, more savings, a compensation fund, investment in greater economic flexibility and response capabilities, and so on. Anything we do counts as a "decision," so we cannot postpone decisions per se. We can and should postpone relatively irrevocable decisions, and under that heading "consumption" is a prime candidate. The correct implication of your argument is that when uncertainty increases, we should (under some specific conditions outlined in my post) consume less, which is close to my point of view...

Victor argues:

I agree on the difficulty in applying option theory to global warming policy. There’s a myriad options with varying cost/lead-time trade-offs. The uncertainties are considerable, have many dimensions, and the flow of information to resolve them is stochastic. But option theory doesn’t always argue for delay. If your doctor said there was a chance you had a flesh-eating bacterial infection that would take several days for the tests to resolve, would you delay or accept treatment? It’s a no-brainer if the treatment was just taking a bottle of antibiotics, but if your arm is turning red immediate hospitalization for intravenous antibiotics might be the optimum strategy. Acting now can preserve options going forward. At a simple level for communication, an insurance framing of the problem works better for me.