Some Bounds on the Sensitivity of Human Population Dynamics to the Effects of Greenhouse-Gas Reduction of Land Productivity

  •  Jack K. Horner    


The 7 August 2019 IPCC special report on land and climate change predicts that the average global temperature will rise more than 1.5 C if human production of greenhouse gases (GHGs) continues at the 2019 rate to 2030, significantly compromising land productivity and the world food supply. Given a relationship between GHGs and land productivity, the World3 simulator can help to bound estimates of the sensitivity of human population dynamics to GHG reduction of land productivity. World3 projects that in the worst case the peak size of the human population could be reduced by 4% - 37% by GHG reduction of land productivity, compared to World3’s “benchmark scenarios”, during calendar years 1900-2100. In particular, World3’s “business-as-usual” (BAU) scenario implies that in the worst case the peak size of the human population would be reduced by ~20% by reduction of land productivity. This BAU-specific result is consistent, to within a factor of two, with GHG/wheat-productivity relations described in the literature.

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