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Conor takes issue with Glonaky’s paper on Climate change. I respond to Conor’s points one-by-one

(1) Goklany’s analysis does not extend beyond the 21st century. This is a problem for two reasons. First, climate change has no plans to close shop in 2100. Even if you believe GDP will be higher in 2100 with unfettered global warming than without, it’s not obvious that GDP would be higher in the year 2200 or 2300 or 3758. (This depends crucially on the rate of technological progress, and as Goklany’s paper acknowledges, that’s difficult to model.) Second, the possibility of "catastrophic" climate change events — those with low probability but extremely high cost — becomes real after 2100.

My general point is that extending beyond a 100 year horizon takes into account values that should be highly discounted. I know the discounting debate is deep and long and deserves far more attention than I can give it here but let me make just a few points.

First, discounting that far matters because there is inherent uncertainty about the usefulness of actions for future generations. The simplest objection is that there is a non-trivial possibility that humanity won’t make it past 2100 anyway.  In that case effort spent saving future children is wasted. I know that sounds a bit nihilistic but it matters.

You cannot die twice. This is why the threat from one hundred 1% probability of death events is not 100%. Dying from one thing cancels out part of the probability of dying from the others. If we didn’t count this effect we would wind up spending all of our time and energy worrying about 1000s of very small probability events.

On a more positive note, there is the possibility that the dangers of global warming or even global warming itself might be mitigated by future technology.  Low cost scrubbing towers for example could allow us to undo  much of the harm that has been created. If these become a possibility by 2100 then damage will have been sustained today for little gain.

I don’t mean to argue for scrubbing towers specifically but to suggest that radical changes are both possible and related to the rate of return on investment. Societies with high economic rates of return and therefore high discount rates are precisely the societies undergoing more rapid change.

Second, discounting matters because generally speaking the things get better in the future. For the most part a transfer from people today to people in 2100 is a transfer from the relatively poor to the relatively rich. Unless we get some things terribly wrong this will be especially true for those in the developing world where real GDP growth rates often exceed 6 or  7 percent.

(2) Goklany’s estimates are based on global aggregates that hide the unequal distribution of the climate change burden. Yes yes, I know Manzi will say that’s not decisive: As long as global GDP is higher, we can redistribute our way out of the problem more effectively tomorrow than we can today. I would be more comfortable with that debate if I thought vast international restributions ofincome in the name of global equity were more likely tomorrow than they are today.

There are at least two issues here that I highlight in Is Waxman-Markey Stealth Aid.

(3) Along those lines, I’m suspicious of the ethical calculus that says we should not focus on one large global problem because larger global problems might exist. That kind of moral math rarely corresponds to the political reality. (Do you think the average congressperson opposed to Waxman-Markey has trouble sleeping at night over new cases of malaria or global hunger?) Nor does it correspond to the historical responsibility: Industrialized nations are more responsible for the global problems created by climate change than the problems of population growth.

Then you really are arguing that Waxman-Markey is Stealth aid and we are going for it for practical reasons? I am not opposed to this but I think the intellectual community should at least be straight forward about it even if the politicians cannot be.  We need to understand what the arguments are and what the real tradeoffs are.

(4) I think Goklany is a bit picky and choosey with the evidence. I always feel uncomfortable making this kind of argument, since empirical disagreements tend to make important differences of worldview look like abstruse technical quibbles. I also like the Goklany paper a lot. But in this case it’s hard to resist.

The carbon fertilization issue is not merely a technical quibble. It goes to the heart of whether or not a warmer world is worse world. This was never intuitively obvious to me for a couple of reasons.

One, the cold sucks. In a world with air conditioning I see few people wishing that the they lived in a cooler place.

Two, there is more land mass and higher development in the northern regions of the world. That is, the places least affected by warming are the places that have the most space and are often the best to move to. There is good reason for many people in the developing world to move to Canada sans global warming. If anything a warmer world might make Canada more attractive.

Lets be clear. I don’t mean to say that we shouldn’t worry about Global Warming because I personally hate the cold – even though a Toronto that was 50 in November would be a beautiful thing.

What I mean to say is that we need to think carefully and deliberately about the consequences and that the results of those deliberations matter. If we find that hunger is greatly increased by global warming, that matters. If we find that vast swaths of Siberia are opened to heavy agriculture and settling, that matters.

There is a lot more to be said on this issue. Including addressing model risk, which is important.