|Fig. 1: Air-conditioners are becoming more and more ubiquitous. (Source: Wikimedia Commons)|
According to a report by the International Energy Agency, the number of air-conditioners worldwide are predicted to increase from 1.6 billion units today to 5.6 billion units by 2050. The prevalence can be seen in windows around the world, as pictured in Figure 1. This could mean that air-conditioners would use as much electricity as China does for all activities today. The greenhouse gas emissions from coal and natural gas plants to power these air-conditioners would increase from 1.25 billion tons in 2016 to 2.28 billion tons in 2050. This is an issue, because the emissions contribute to global warming, which could further increase the demand for air-conditioning in a vicious cycle. 
Air conditioning is contributing to the detrimental effects of climate change. Climate change represents the biggest global health threat of the 21st century, and is already responsible for more heat waves, extreme weather, the spread of disease, increasing pollution, and reduced productivity. The direct effects include storms, floods, and fires, and also indirect effects such as hospitals shutting down, home loss, and rise in mental health problems.  This will become an increasing issue. 90% of American households have air-conditioning, and in Africa, Asia, Latin America and the Middle East, only about 8% of the population owns an air-conditioner. As incomes rise, more people are installing air-conditioners. 
However, air-conditioning has many benefits for quality of life and health, and home air-conditioners in the US has cut premature deaths on hot days by 75 percent since 1960.  Additionally, a study led by Harvard T.H Chan School of Public Health demonstrated the detrimental cognitive effects of indoor temperatures during a heat wave on healthy individuals. The study found extreme heat linked with reduced cognitive performance among young adults in non-air conditioned buildings. According to one of the lead authors of the study, most research on the health effects of heat focuses on vulnerable populations, but the general population is also at risk from heat waves. It is essential to understand the impact on different populations that rising temperatures will have. 
We certainly can't get rid of air-conditioners because of their benefits, but we need to focus scientific research and innovation on making them more energy efficient. This way, we can continue to receive the benefits, but not exacerbate the problems.
© Laura Jacobsen. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 K. Pierre-Louis, "The World Wants Air-Conditioning. That Could Warm the World," New York Times, 15 May 18.
 N. Watts et al., "The 2018 Report of the Lancet Countdown on Health and Climate Change: Shaping the Health of Nations for Centuries to Come," Lancet 392, 2479 (2018).
 J. G. Laurent, et al., "Reduced Cognitive Function During a Heat Wave Among Residents of Non-Air-Conditioned Buildings: An Observational Study of Young Adults in the Summer of 2016," PLOS Medicine 15, e1002605 (2018).