Saturday, June 23, 2012

Population weight, public health, and environmental implications

I watched the following video

which brought up several points of concern:
  1. The total adult population of the Earth weighs roughly 287 million metric tons (316 million US tons).
    • This is about 1/2 of the total biomass of the world's cattle
    • This is about 1/5 of the total biomass of the world's ants
  2. The world's average adult body mass is 62 kg (137 lbs).
  3. The North American average adult body mass is 80.7 kg (178 lbs).
  4. If the world's adult population all had the same average mass as the North American average, it would be like adding 935 million people to the current world's population.
The video goes on to explain why this is problematic for environmental and public health concerns (starting from 1:14). The original article - "The Weight of Nations: An estimation of adult human biomass" - can be found at BMC Public Health.

Abstract (Background):
The energy requirement of species at each trophic level in an ecological pyramid is a function of the number of organisms and their average mass. Regarding human populations, although considerable attention is given to estimating the number of people, much less is given to estimating average mass, despite evidence that average body mass is increasing. We estimate global human biomass, its distribution by region and the proportion of biomass due to overweight and obesity.
Abstract (Results & Conclusions):
In 2005, global adult human biomass was approximately 287 million tonnes, of which 15 million tonnes were due to overweight (BMI > 25), a mass equivalent to that of 242 million people of average body mass (5% of global human biomass). Biomass due to obesity was 3.5 million tonnes, the mass equivalent of 56 million people of average body mass (1.2% of human biomass). North America has 6% of the world population but 34% of biomass due to obesity. Asia has 61% of the world population but 13% of biomass due to obesity. One tonne of human biomass corresponds to approximately 12 adults in North America and 17 adults in Asia. If all countries had the BMI distribution of the USA, the increase in human biomass of 58 million tonnes would be equivalent in mass to an extra 935 million people of average body mass, and have energy requirements equivalent to that of 473 million adults.

Increasing population fatness could have the same implications for world food energy demands as an extra half a billion people living on the earth.
I (idly) wonder if anyone has used this sort of data analysis for actual trophic food web analysis, much like one might do with various fish species (e.g., here, here, here, here, here, here, here, and here; see also "trophic food web" on the University of Michigan's dissertations, theses, and research publications site).

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