Gaia’s Limits

This illustrated essay concerns sustainability. Its simple thesis is that trees do not grow to the sky. Basic facts are used to figure Earth’s human carrying capacity. Results are more optimistic than past neo-Malthusian predictions, but limits are still reached within present lifetimes.


Two inevitable capacity limits emerge. One is a soft food limit arising around 2050 from fundamental crop science. Arable land and water are finite. Crop intensification using those resources is reaching limits, and will slowly continue to do so. The other is a hard energy limit arising from inevitable fossil fuel depletion. The essay details liquid transportation fuels, making energy depletion graphically clear at a visceral level. Future tradeoffs between food and inevitable biofuel carrying capacity set firm upper limits on eventual population. These important issues and possible responses are not addressed by U.S. dysfunctional public policy, reviewed in the final section.