The boom in air conditioning is good news for many reasons. Studies show that it lowers mortality during heat waves. Heat makes prison inmates fractious - air conditioning pays for itself by reducing fights. When the temperature exceeds 21C or 22C in exam halls, students start to score lower in maths tests. In offices, air conditioning makes us more productive: according to one early study, it made US government typists do 24% more work. Economists have since confirmed that relationship between productivity and keeping cool.
Inconvenient truth William Nordhaus divided the world into cells, by lines of latitude and longitude, and plotted each one's climate, output and population. The hotter the average temperature, he found, the less productive the people.
but airconditioning also causes the outside environment to get hotter:
A study in Phoenix, Arizona, found the hot air pumped out of air conditioning units increased the city's night-time temperature by 2C,
so, instead of being 105 degrees, it is 108 degrees. On the other hand, the people are cooler.
one major worry of environmentalists is that it will take a lot more electricity to run these airconditioners as they get bought by the growing Asian middle class.
And of course if you are inside a closed bedroom with your air conditioner on, you are less likely to get Dengue fever (or malaria or Zika virus).