Getting the Tube home last night my eye was drawn to a man reading The Sun. “Fatties cause global warming” screamed the front page. “Oh really?” I thought. “And here I was blaming it on CO2 emissions.”
The news comes from a paper in the International Journal of Epidemiology, entitled Population adiposity and climate change. Adiposity being an overly-scientific term for “fatness”, that is.
Dr Phil Edwards of the London School of Hygiene and Tropical Medicine and his colleague Ian Roberts modelled two possible populations, one “normal” with 3.5% obese people and another “overweight” with 40% obese, as measured by a Body Mass Index of 30. Both population consists of a billion people. They say that the normal population reflects the UK in the 1970s, whilst the overweight population is the prediction for 2010.
By estimating the energy required by both populations they found that the overweight population would require 19% more energy than the normal population. This of course means the overweight population would need to consume 19% more food. Producing this extra food would result in 270 megatonnes of extra greenhouse gasses (meaning CO2 as well as other gases like methane) being released into the atmosphere.
An overweight population would also release further greenhouse gases through increased reliance on transport. Newton’s laws of motion tell us that moving a heavier mass requires a proportionally larger force, so we would expect heavier car drivers to use more petrol. Overweight people are also more likely to drive rather than walk, compounding the effect. In total this would add another 170 megatonnes of greenhouse gasses to the atmosphere.
All of these figures are really extended back-of-the-envelope calculations. In the paper, the authors admit to making many assumptions about the two populations, such as keeping everyone of the same sex at the same height, and using identical levels of activity for both normal and obese people. As such, I wouldn’t take these figures as literal, but they do indicate that an overweight population has some effect on climate change.
Does this research mean then that a global diet is in order? Eat carrots, stop climate change? No. Food production accounts for only 20% of emissions, according to the paper, so in a planet of one billion people as imagined by this model we’re still left with 6000 megatonnes of greenhouse gasses being pumped out by other industries.
Tackling climate change requires a transformation in the way we consume and generate energy. The Sun story paints it as a problem caused by “fatties” – an easy scapegoat, but we’re all to blame. The obesity crisis is an issue that must also be tackled – nearly half of the population obese by next year is insane – but it’s not a magic bullet for climate change. Nothing is.