By Janet Fang
Posting in Energy
If everyone weighed the same as Americans, the increase in human biomass would equal an extra 935 million people. To support that extra weight, energy requirements must increase by 481%.
The weight of the world is 287 million tonnes.
That’s the global adult human biomass in 2005, and according to a new report, we need to better consider the ecological effects of obesity. Increasing population fatness could have the same implications for world food energy demands as an extra half a billion people living on the earth.
To calculate total biomass, the researchers multiplied population size and average body mass. To estimate average adult body mass for each county, they used data on body mass index (BMI) and height distribution collected in 2005 by the United Nations, the World Health Organization, and the US Agency for International Development.
In case the units are confusing… 287 million tonnes (or metric tons) is about 316 million tons, or over 5400 Titanics.
Other highlights (a bit number heavy but fascinating):
- Globally, people with average body mass weighed about 137 pounds.
- Of the 287 million tonnes of humanity, 15 million tonnes were due to overweight people (BMI > 25). That’s 5% of global human biomass.
- That’s the mass equivalent to that of 242 million people of average body mass (or 170 military aircraft carriers of extra weight).
- Biomass due to obese people (BMI > 30) was 3.5 million tonnes, the mass equivalent of 56 million people of average body mass. That’s 1.2% of human biomass.
- That’s a mass equivalent of 56 million people of average body mass.
- 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 US, where 36% of the population is obese:
- There would be an increase of 58 million tonnes.
- That increase in human biomass would be equivalent in mass to an extra 935 million people of average body mass…
- And have extra energy requirements equivalent to that of 473 million adults.
- In other words, the amount of energy required to support all that extra weight would increase by 481%.
Larger people require more food and energy, and the resource requirements will just keep on swelling if there’s going to be 9 billion humans by 2050. Although the largest increase in population numbers is expected in Asia and sub-Saharan Africa, these results suggest that population increases in the US will carry more weight than would be implied by numbers alone.
"When people talk about sustainability, they quickly get into concerns about population," says study researcher Ian Roberts of the London School of Hygiene and Tropical Medicine. But while we need to slow population growth, overconsumption is just as much of a problem. "This is a statistic that measures both," Roberts adds.
The study was published in BMC Public Health.
Image by D Sharon Pruitt via Flickr
Jun 18, 2012
It's as if the authors of the original study ran out of time the night before the paper was due, and just decided to ignore that children weigh less than adults. Think I'm joking? Let them tell you in their own words: "Finally, we did not estimate biomass in children who comprise a significant proportion of the population in many countries, [...] Future work in this area should account for population age structure". Why even provide an estimate with 3 significant digits? Should you trust any other data from the study?