Monday, December 14, 2009

Population Control a Solution to Human-Induced Global Climate Change?


I've seen more than a few suggestions that population is the problem to global warming/global climate change and therefore The Solution is population control.

There are three, surprisingly unrelated issues in the above statement.

First, the world is probably overpopulated. There are all kinds of discussions of the carrying (PDF) capacity (PDF) of the Earth. Most conclude that we've met that carrying capacity and that we're living on borrowed time. How much time is, of course, not clear.

As some examples of the idea that we've reached the limit of our ecosystem's carrying capacity:

In 1999, it was estimated that the world had about 116 days of food reserves stored. That is, if all food production stopped, we'd have about 116 days of food available to feed everyone in the world. As of 2006, those reserves had shrunk to 56 days.

Many people (PDF) agree (PDF) that we've reached the peak of oil production and that oil and its derivatives will become more and more difficult to acquire. That matters because all kinds of quality of life issues are directly related to availability of (cheap, easy) energy supplies. That is, we can extend the carrying capacity of an ecosystem by introducing external energy sources.

Human-induced global climate change is due, basically to resource utilization. There are too many of us and we're consuming too much energy making too much stuff.

From those three examples, I'm going to move on with the assumption that everyone agrees that we've reached (some kind of) carrying capacity of our ecosystem. That is, the earth is overpopulated by humans.

Can we solve that last example by limiting births? First, we have to understand the problem. I've posted several times about the problem of human-induced climate change. The biggest problem with our releasing of CO2 into the atmosphere is that there is a lot of inertia in the atmosphere. We're at 385.99 parts per million by volume CO2 (ppmv) in the atmosphere. During the Cretaceous, the atmosphere was at 340 ppmv but was 5 degrees C warmer (on average). Why aren't we this warm yet? Because it takes time for the atmosphere to respond. We may not get that warm this time, but even if we cut all CO2 emissions to 0, we'd still warm at least 1 to 2 degrees C over the next few centuries.

That's where the problem comes in. The scientific publications and the press are talking about 2050 (or something similar) as a target date for limiting CO2 concentrations, but we're already above the concentrations that will push us to 2 or more degrees C of warming and all of the associated problems. Those problems will not be slight, nor will they be easy to adapt to, but they will not be completely catastrophic for the entire human race. Some people in some places will suffer a lot more than others.

Now, with that in mind, let's go back to the idea of population control. We're expected to hit seven billion people within the next decade. For this little thought experiment, let's go with something simple and say we have no (0) births for 10 years. That is, we leave the world population at 6,790,062,216 (July 2009 est.) for the next 10 years. Our emissions of CO2 are growing at a rate of about 2-3% per year. Assuming all of that is due to population increases (which it isn't) and we would stop increasing our CO2 emissions (but not stop emitting), we'd still be emitting about 1.8 ppmv per year. So, we'd still be increasing our CO2 emissions over the 10 years of no population additions (and some population decreases, which I'm ignoring for the moment). So, we wouldn't stay at 385.99 ppmv over the decade of no births. We'd still be increasing, and we'd still be causing irrecoverable harm.

I ignored deaths in the above estimates. Let me correct that here. Let's assume, for a second, that the 1.8 ppmv of CO2 emissions per year is evenly distributed to all humans (it's not--more in a bit). Let's also assume the CIA estimate for death rate (8.2 per 1,000 people) is an accurate average. First, there is an average of 56 million deaths per year (assuming no increase) for the decade of no births. That's a decrease in the world population of 560 million people. Out of 6790 million people. We'd be down to 6230 million people (6.23 billion). Let's now go back to emissions. 1.8 ppmv per year for all 6790 million people is about 2.7 x 10^-4 ppmv per person per year. If we had "only" 6230 million people at the end of the decade, we'd be down to 1.65 ppmv per year. Or a rather slight decrease in emissions by the end of the decade of no births. We'd still be emitting too much, and it would be too late to do anything about it!

There's a huge problem with all of the above: Emissions are not equally divided. In fact, the five largest energy users (68%) account for only 36% of the world's population. That means that controlling population will only have an effect on emissions after many generations, by which time it would be way too late.

We need to control emissions, not population. At some point we'll have to deal with population, but it's NOT the solution to human-induced global climate change. It's not even A solution. It's a solution to exceeding carrying capacity, but it would be too little, too late to affect climate change... Unless people are advocating the removal of the 36% who pollute the most, which I'm sure is not the case since most of the people advocating population control are a part of that 36%. Even if we killed off "the other" 64% of the population as a "solution" we'd only buy ourselves a few decades at our current consumption.

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