> "Projecting forward 20 years that means that we expect gross world product to increase 84%. If we go carbon neutral and the final gross world product ends up at 2% less than this simple projection, it grows about 80.5% instead. Thus we'd reduce the amount of total growth by about 4%."

Hold on, that sounds nothing like what you originally said. I quote, "Spending about 2% of current world domestic product on CO2 mitigation seems perfectly justifiable to me."

'2% of current world domestic product' is rather different from '2% of world GDP 80 years from now'.

> Thus we'd reduce the amount of total growth by about 4%. Take a 20th power and we find that the amount of growth in the end is reduced by a factor of 0.2% per year, compounding annually. Note that when I say 0.2% I don't mean that it would be 2.9% instead of 3.1%. Instead I mean that it would be 3.0934..% instead of 3.1%.

I don't follow your calculations here. When I plug in 3.09% into a compound interest calculator instead of 3.1%, after 20 years I get the same 184% answer. If you suggest we can have our cake & eat it too, I suspect your math is screwy somewhere...

> 1. Projections by scientists say global warming threatens food supplies, resulting in potential starvation. 2. Projections by the CIA predict substantially increased geopolitical instability. This is likely to result in wars killing lots of people. 3. The World Health Organization claims that 2.4 million people die each year from air pollution. Today. Continued increases in industrialization on the current model would increase this figure substantially. A move to seriously replace fossil fuels would save many to all of these lives.

1. from the IPCC: "Crop productivity is projected to increase slightly at mid- to high latitudes for local mean temperature increases of up to 1-3°C depending on the crop, and then decrease beyond that in some regions. At lower latitudes, especially seasonally dry and tropical regions, crop productivity is projected to decrease for even small local temperature increases (1-2°C), which would increase the risk of hunger. Globally, the potential for food production is projected to increase with increases in local average temperature over a range of 1-3°C, but above this it is projected to decrease."

But hey, since you're willing to assume perfect politics, then shouldn't I be allowed to assume that any surplus will be distributed to those who need it? (Actually, if we're assuming perfect politics, this is utterly irrelevant - there is far more food produced than necessary to feed everyone, after all.)

Dislocation from changes in agricultural productivity are one-time costs, Malthusian-style; and can be offset by better farming. We can spend trillions offsetting warming, or we can invest some billions into getting affected farmers better irrigation or fertilizers, or just relocating them. I know which I prefer.

2. Projections by the CIA predict substantially increased geopolitical instability. This is likely to result in wars killing lots of people.

Again, one-time costs, as opposed to eternal mitigation costs or opportunity costs; and as for straight deaths, it's not like cold doesn't kill dozens of thousands a year, every year: http://www.wired.com/science/planetearth/news/2005/03/66981

3. Global warming efforts are only loosely linked to fighting the kind of pollution that kills people. Putting some carbon sequestration equipment on a coal plant doesn't much affect the particulates that kill people. And historically, per the environmental Kuznets Curve, deaths from pollution are reduced by further economic development & not by fighting some tangential cause. You want China to stop killing so many of its people with coal plant emissions? Let China develop to the point where the benefits of the cheap coal power is less than the destruction of human capital & degradation of life - development that would be hampered by taxing everything related to carbon emissions or calls to have everyone switch to driving Priuses or something.

> After considering those factors I think that I am on solid grounds to claim that a serious attempt to solve global warming, even if it is done stupidly, is likely to save far more lives than the resulting potentially poor allocation of resources will cost.

If it's done stupidly, it'll do nothing whatsoever for the issues, constitute a massive waste of resources. (People are bandying around programs spending billions & trillions of dollars. Those are the sort of resources that could fund Manhattan Projects on things like cancer or aging.) And remember, even the crash interventions still say that temperatures will rise significantly.

> With the difference measured in the millions of lives/year. (Depending on what value you give each life, this alone could justify the whole project without even considering longer-term consequences.)

(I wouldn't value the lives too much, as they will almost all be very poor Third-worlders, because that's the region of the world affected and the sort of people who can't or won't adapt.)