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Meat and dairy When animals are fed human-edible crops, this is the most inefficient part of the global food supply in terms of calories, protein and micro-nutrient terms. The inefficiency is also costly in greenhouse gas terms especially when the animals are ruminants (sheep and cattle) and typically double their impact through the belching of methane. Other problems include the two thirds of the world's antibiotics that are used in animal farming, and the welfare of the beasts themselves.

Over 1% of the world's total GHG footprint could be saved by simple improvements to the way rice is usually grown. This is a big untold story. It has nothing to do with the fossil fuel used by tractors, lorries, boats or any other parts of the supply chain. Specifically, what is needed is more judicious use of fertiliser and not flooding paddy fields22. Paddy field methane is about 6% of all greenhouse gas emissions from the food supply chain. I've seen photos of rivers in China that are bright green from so much excess fertiliser; the yield is probably actually suffering from over application.

Methane In the phrase 'coal, oil and gas', methane is the gas we are talking about. As well as being commercially extracted, it is also produced by cows and sheep when they chew the cud (ruminate), by paddy fields if they are flooded, it pours out of permafrost if it melts, and is produced by rotting organic matter in landfill sites. When burned it releases a lot of heat energy (that's good) but produces carbon dioxide (that's bad). Much more problematic is that if it is released into the atmosphere without burning it is a much more powerful greenhouse gas than carbon dioxide. In fact if you compare the global warming impact of methane over 20 years to the same weight of carbon dioxide of that period you find it is 76 times worse. However, methane only has a half-life of about 12 years in the atmosphere, so over a 100-year period, the slow acting but long lasting carbon dioxide has caught up a bit and the methane is 'only' 25 times worse. There is an arbitrary convention to take a 100 years' timeframe, for most purposes. However, there is a very strong case for being interested in much shorter timescales than this, in which case methane needs to be considered as an even more powerful greenhouse