it didn't occur to Bill that the terms P (population) and S (services) are negotiable?

declineofempire |  Bill Gates recently wrote his annual letter and it's getting some attention because he addressed the climate problem this year (a Vox interview with Ezra Klein). The target audience was high school students. The letter contained a simple mathematical formula describing why solving the climate problem is very hard. Here it is, with Bill's explanation.

Bill Gates: Yeah, it's important for people who care about climate to not think it's easy to solve.

The equation is: How many people are there? And that's P, which today is about 7 billion, and will grow to be bigger than 9 billion.

Then you take how many energy-related services each person takes advantage of — that's heating, cooling, transport, lighting. We call that S, and that will go up quite a bit as poor people in India are getting lighting, air conditioning, refrigeration. The average number of services used by a person will increase, and it should — that's a very good thing.

Then you have E, the energy used per service. In some areas, like lighting, that number can go down a lot. In some, like transport, planes, making fertilizer — those processes are extremely optimized, and so there's not that much room to innovate on the energy-per-service front. Even if you're optimistic about that, maybe you'll get to 0.6. That is, 40 percent more efficient across all services.

And so if we take these first three factors — 7 billion going to 9 billion, double the services per person, and efficiency at about 0.6, that's increasing [emissions].

The last factor is C, the carbon per unit of energy. And so if you multiply today, you get 36 billion tons. And if you multiply in the future, you need to get zero.

And so the first three factors are not going [to change] — the first one is going up; the second one, hopefully, is going up; the third one is going down, but not enough to offset those other two.

You have to take transport, industry, household, electricity — and, at least in the middle income and rich countries, put it into a zero emission mode.

Gates believes we need a "miracle" to get to zero carbon emissions in a world of 9 billion people, most of whom are wealthier (a doubling in terms of services S) than they are now.