JDN 2456941 PDT 12:25.

Paul Krugman recently wrote a column about the “limits to growth” community, and as usual, it’s good stuff; his example of how steamships substituted more ships for less fuel is quite compelling. But there’s a much stronger argument to made against “limits to growth”, and I thought I’d make it here.

The basic idea, most famously propounded by Jay Forrester but still with many proponents today (and actually owing quite a bit to Thomas Malthus), is this: There’s only so much stuff in the world. If we keep adding more people and trying to give people higher standards of living, we’re going to exhaust all the stuff, and then we’ll be in big trouble.

This argument seems intuitively reasonable, but turns out to be economically naïve. It can take several specific forms, from the basically reasonable to the utterly ridiculous. On the former end is “peak oil”, the point at which we reach a maximum rate of oil extraction. We’re actually past that point in most places, and it won’t be long before the whole world crosses that line. So yes, we really are running out of oil, and we need to transition to other fuels as quickly as possible. On the latter end is the original Mathusian argument (we now have much more food per person worldwide than they did in Malthus’s time—that’s why ending world hunger is a realistic option now), and, sadly, the argument Mark Buchanan made a few days ago. No, you don’t always need more energy to produce more economic output—as Krugman’s example cleverly demonstrates. You can use other methods to improve your energy efficiency, and that doesn’t necessarily require new technology.

Here’s the part that Krugman missed: Even if we need more energy, there’s plenty of room at the top. The total amount of sunlight that hits the Earth is about 1.3 kW/m^2, and the Earth has a surface area of about 500 million km^2, which is 5e14 m^2. That means that if we could somehow capture all the sunlight that hits the Earth, we’d have 6.5e17 W, which is 5.7e18 kilowatt-hours per year. Total world energy consumption is about 140,000 terawatt-hours per year, which is 1.4e14 kilowatt-hours per year. That means we could increase energy consumption by a factor of one thousand just using Earth-based solar power (Covering the oceans with synthetic algae? A fleet of high-altitude balloons covered in high-efficiency solar panels?). That’s not including fission power, which is already economically efficient, or fusion power, which has passed break-even and may soon become economically feasible as well. Fusion power is only limited by the size of your reactor and your quantity of deuterium, and deuterium is found in ocean water (about 33 milligrams per liter), not to mention permeating all of outer space. If we can figure out how to fuse ordinary hydrogen, well now our fuel is literally the most abundant substance in the universe.

And what if we move beyond the Earth? What if we somehow captured not just the solar energy that hits the Earth, but the totality of solar energy that the Sun itself releases? That figure is about 1e31 joules per day, which is 1e27 kilowatt-hours per day, or seven trillion times as much energy as we currently consume. It is literally enough to annihilate entire planets, which the Sun would certainly do if you put a planet near enough to it. A theoretical construct to capture all this energy is called a Dyson Sphere, and the ability to construct one officially makes you a Type 2 Kardashev Civilization. (We currently stand at about Type 0.7. Building that worldwide solar network would raise us to Type 1.)

Can we actually capture all that energy with our current technology? Of course not. Indeed, we probably won’t have that technology for centuries if not millennia. But if your claim—as Mark Buchanan’s was—is about fundamental physical limits, then you should be talking about Dyson Spheres. If you’re not, then we are really talking about practical economic limits.

Are there practical economic limits to growth? Of course there are; indeed, they are what actually constrains growth in the real world. That’s why the US can’t grow above 2% and China won’t be growing at 7% much longer. (I am rather disturbed by the fact that many of the Chinese nationals I know don’t appreciate this; they seem to believe the propaganda that this rapid growth is something fundamentally better about the Chinese system, rather than the simple economic fact that it’s easier to grow rapidly when you are starting very small. I had a conversation with a man the other day who honestly seemed to think that Macau could sustain its 12% annual GDP growth—driven by gambling, no less! Zero real productivity!—into the indefinite future. Don’t get me wrong, I’m thrilled that China is growing so fast and lifting so many people out of poverty. But no remotely credible economist believes they can sustain this growth forever. The best-case scenario is to follow the pattern of Korea, rising from Third World to First World status in a few generations. Korea grew astonishingly fast from about 1950 to 1990, but now that they’ve made it, their growth rate is only 3%.)

There is also a reasonable argument to be made about the economic tradeoffs involved in fighting climate change and natural resource depletion. While the people of Brazil may like to have more firewood and space for farming, the fact is the rest of need that Amazon in order to breathe. While any given fisherman may be rational in the amount of fish he catches, worldwide we are running out of fish. And while we Americans may love our low gas prices (and become furious when they rise even slightly), the fact is, our oil subsidies are costing hundreds of billions of dollars and endangering millions of lives.

We may in fact have to bear some short-term cost in economic output in order to ensure long-term environmental sustainability (though to return to Krugman, that cost may be a lot less than many people think!). Economic growth does slow down as you reach high standards of living, and it may even continue to slow down as technology begins to reach diminishing returns (though this is much harder to forecast). So yes, in that sense there are limits to growth. But the really fundamental limits aren’t something we have to worry about for at least a thousand years. Right now, it’s just a question of good economic policy.