This week The Economist published a leader and a main article on sustainable air conditioning. leader: https://www.economist.com/leaders/2018/08/25/how-to-make-air-conditioning-more-sustainable WHAT is the single most effective way to reduce greenhouse-gas emissions? Go vegetarian? Replant the Amazon? Cycle to work? None of the above. The answer is: make air-conditioners radically better. On one calculation, replacing refrigerants that damage the atmosphere would reduce total greenhouse gases by the equivalent of 90bn tonnes of CO2 by 2050. Making the units more energy-efficient could double that. By contrast, if half the world’s population were to give up meat, it would save 66bn tonnes of CO2. Replanting two-thirds of degraded tropical forests would save 61bn tonnes. A one-third increase in global bicycle journeys would save just 2.3bn tonnes. main article: https://www.economist.com/international/2018/08/25/air-conditioners-do-great-good-but-at-a-high-environmental-cost At the moment, only 8% of the 3bn people in the tropics have air-conditioning, compared with over 90% of households in America and Japan. But eventually, it will be near universal because so many trends are converging behind its spread: ageing, since old people are more vulnerable to heat stroke; urbanisation, since fields cannot be air-conditioned but offices and factories must be; and economic growth, since, after mobile phones, the middle class in emerging markets want fans or air-conditioners next. Note that the GHG impact is mostly about refrigerant gases, not electricity. But electricity plays a role too. At the moment, according to the IEA, it takes about 2,000 TWhs (terawatt hours) of electricity to run all the world’s cooling machines for a year. This produces 4bn tons of CO2, 12% of the total. Without drastic improvements in air-conditioners’ efficiency, the IEA reckons, they will be burning up 6,000 TWhs by 2050.