We have worried before about what will happen when citizens of China and India all get air conditioners. At American Scientist, Michael Sivak does the math and it isn't pretty.
Sivak writes that 87% of American households now have AC, and use 185 billion Kilowatt-hours running them. Air conditioning use in China has exploded, and 50 million units were sold in 2010 alone. This is all just due to economic growth and doesn't even take climate change into account.
It won't be as bad as that; there are cultural differences in how people use air conditioning, 18 Celsius is a low base number and most Americans live in single family houses where it is likely that Chinese and Indians live in smaller apartments. Sivak acknowledges this:
Several caveats are in order. Cooling degree days, being a temperature measure, does not represent all factors that are relevant to the potential demand for cooling. Some other considerations include the extent of local cloud cover, humidity, the amount of interior space to be cooled per person, and differences in dwelling construction and their effects on thermal insulation. Variations in the energy efficiency of air conditioners across countries were not included in this analysis. In addition, cultural differences in the tolerance of hot temperatures and in environmental responsibility were beyond the scope of this study.
But it is still scary. As William Saletan wrote a few years ago in Slate:
Air conditioning takes indoor heat and pushes it outdoors. To do this, it uses energy, which increases production of greenhouse gases, which warm the atmosphere. From a cooling standpoint, the first transaction is a wash, and the second is a loss. We're cooking our planet to refrigerate the diminishing part that's still habitable.