Tre økonomer om global oppvarming

Hjemmeeksamenstid, så bare et kort innspill før det stupes tilbake i bøkene:

Global oppvarming er altså et faktum. Usikkerheten omkring utfallet gir stor grunn til bekymring. Ofte kan vi se an konsekvensene før vi handler, men hva om en mulig konsekvens er at endringene er fullstendig irreversible og direkte ødeleggende? Økonomer ønsker selvsagt også å si noe om saken. Her er eksempler på tre økonomibloggeres innspill i klimadebatten: Greg Mankiw er en ivrig forsvarer av en karbonavgift heller enn kvoter, Tyler Cowen er opptatt av usikkerhetsaspektet og mangelen på realistiske løsninger mens Brad DeLong tenker på forskjellen på risiko og usikkerhet. Klimasaken oppsummeres strålende i en tegneserie på slutten.

N. Gregory Mankiw:

The scientists tell us that world temperatures are rising because humans are emitting carbon into the atmosphere. Basic economics tells us that when you tax something, you normally get less of it. So if we want to reduce global emissions of carbon, we need a global carbon tax. Q.E.D. […]

Those vying for elected office, however, are reluctant to sign on to this agenda. Their political consultants are no fans of taxes, Pigovian or otherwise. … Yet this natural aversion to carbon taxes can be overcome if the revenue from the tax is used to reduce other taxes. By itself, a carbon tax would raise the tax burden on anyone who drives a car or uses electricity produced with fossil fuels, which means just about everybody.

Tyler Cowen:

It is by now pointless to deny that global warming is man-made to a considerable degree. […]

It is a very real problem. If you don’t believe me, go visit the deltas of East Bengal or Bangladesh and think about it again. […]

I do not much trust climate models. Perhaps I have spent too much time doing macro, and the experience carries over. Nonetheless uncertainty about final effects gives us more to worry about, not less. It is the worst-case scenarios for global warming which worry me, not the middling scenarios. Variance is our enemy in this matter. […]

I have yet to see a real plan which recognizes three points: a) without continued economic growth the world will probably fall apart, b) the problem is real and significant, c) any good preventive solution would require an enormous amount of concerted action across both time and across nations.

Brad DeLong:

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.

Til slutt en treffende tegneserie: