Earth to reach boiling point in 400 years

As an ex-physicist who realises later in life that he’d probably rather have studied economics, I’d like to paraphrase from an interesting article by Tom Murphy. It uses fundamental physics to argue that economic growth cannot continue indefinitely, albeit under the assumption that increases in GDP require an increased use of energy*:

US energy consumption has increased by about 3% per year for several centuries.This is partly due to increases in population, but per-capita energy use itself has grown also — our energy lives today are far richer than those of our great-great-grandparents a century ago.

So even if population stabilizes, it’s fair to say we are accustomed to per-capita energy growth.

The Earth has only one mechanism for releasing heat to space, and that’s via infrared radiation. It’s well understood. If we use more energy (it must all end up as heat energy) then more must be radiated away, and the surface temperature of the planet will increase.

This graph, which presumes a constant 2.3% energy increase per year, plots the Earth’s surface temperature over time:

The upshot is that at a 2.3% growth rate, the Earth would reach boiling temperature in about 400 years. This statement is independent of technology. Even if we don’t have a name for the energy source yet, as long as it obeys the laws of thermodynamics, we cook ourselves with perpetual energy increase. Thermodynamic limits impose a cap to energy growth due to the process of radiating the spent energy away.

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*Under a model in which GDP is fixed, with conditions of stable energy, stable population, and steady-state economy, then if we accumulate knowledge, improve the quality of life, and thus create an unambiguously more desirable world this is a form of economic growth, but one which more normally falls under the title of “development” rather than “growth”.