I made some comments about a post by Kerry Emanuel at the National Climate Change Forum. Andrew Dessler first commented:

John: here’s how I would look at the issue. Imagine you’re a citizen year 2100. If it turns out that the climate sensitivity is high and human society does nothing about it, then you would rightfully be pretty angry.

I responded as follows:

Andrew Dessler writes: “John: here’s how I would look at the issue. Imagine you’re a citizen year 2100.”

OK. Let’s imagine that. In the 20th century, worldwide GDP/income growth averaged about 2.3% per year. Let’s assume that continues. Therefore, as a citizen of the world in 2100, my income is approximately 7 times what it was for the citizens of the world in 2014. Let’s further assume that there are 10 billion of us in 2100 (a nice round and reasonable number). Therefore, our global income/GDP in 2100 is approximately 10 times higher than at present (7 times more GDP/income per person, and approximately 1.4 times as many people). Therefore, our global annual GDP is about $900 trillion (~10 times the 2014 value of $90, purchasing power parity basis), and our global income is about 80% of that, or $720 trillion.

Let’s further ...suppose that the global CO2 concentration is about 700 ppm, and this has resulted in a warming of 5 degrees Celsius relative to the year 2014. (Note that such warming seems extremely improbable, because *average* warming rate over the next 8 decades that’s more than 3 times the current rate.) Let’s further suppose that this warming of 5 degrees Celsius cuts the income/GDP-per-person for the citizen of 2100 from 7 times the value of the citizen of 2014 to 6 times the value of the citizen of 2014 (i.e., about a 14% reduction in income).

Suppose we citizens of 2100, suffering from a 14% reduction in our income due to global warming, decide to spend 20% our income on pulling CO2 from the atmosphere and injecting it underground (ambient air capture and sequestration). That 20% of our income would be $720 trillion times 0.86 (from a 14 percent reduction caused by the hypothesized 5 degrees Celsius global warming) times 0.20 (20 percent) = $124 trillion a year. One (pessimistic) estimate of the cost of ambient air capture and sequestration in 2012 was $1000 per metric ton of CO2 (http://www.pnas.org/content/108/51/20428.long). (Note that this paper also mentions other estimates for the current cost at “no more than a few hundred dollars per tonne of CO2 avoided.”) Since there are 2.13 gigatonnes of carbon per ppm of CO2 in the air, and 3.67 tonnnes of CO2 per tonne of carbon, the total cost to remove 1 ppm of CO2 from the atmosphere at $1000 per metric ton would be $7.8 trillion. So if we citizens of 2100 spent 20% of our income (i.e., $124 trillion per year) on ambient air CO2 removal and sequestration, we could remove about 16 ppm per year. Let’s say were adding 2 ppm a year at the time; therefore, we could only lower CO2 by 14 ppm per year. So how many years would it take us to get from 700 ppm down to the pre-industrial concentration of 280 ppm? It would take us (700 – 280)/14 = 30 years.

At the end of that 30 years, assuming that GDP per capita continued to grow at 2.3% per year, and even assuming that we continued to lose 14% of our income to climate change damage and 20% of our income was spent on ambient CO2 removal and sequestration, our income would still be 6.8 times the income of the average citizen of 2014 (i.e. 1.4 times the average income of the citizen of 2100, which was 4.8 times the average income of the citizen of 2014).

Dr. Dessler continues, “If it turns out that the climate sensitivity is high and human society does nothing about it, then you would rightfully be pretty angry.”

How do we citizens of 2100 have any “right” to be “pretty angry?” We have an income that is 4.8 times higher than the average citizen of 2014. And that’s even *assuming* that there is 5 degrees Celsius of warming between now and 2100 (which is very unlikely to happen) and that such warming causes a 14% loss in income from climate damage, AND that we citizens of 2100 spend 20% of our incomes removing CO2 from the ambient air and sequestering it. Furthermore, by 2130, we average citizens will have an incomes that are 6.8 times higher than the average citizen of 2014, and will have lowered the ambient air CO2 concentration to the pre-industrial value of 280 ppm.

My comments are essentially a follow-up on posts I've made here on my blog that question the morality of sacrificing for the benefit of the people of 2100, since I think they'll be so much better off than the people of 2014. (Or they'll be waging and likely losing a war to super-intelligent terminators, and so will have much bigger worries than global warming.)

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