I assure you that doing something like installing ACs in every home in Seattle would incur a massive cost, and it is not guaranteed that such a measure would ever be necessary at any point in the next 100 years.
What does that have to do with power grid failures?
Also having AC, even if it's not necessary, can be very useful.
"Seattle averages 24 days a year when the thermometer reaches into the 80s °F (over 27 °C). The temperature typically climbs to 90 °F (32 °C) on just one or two days a year."
That's high enough to cause a serious reduction in productivity/enjoyment. If the average person is exposed to those temperatures for 3 hours a day as a lack of home AC, and loses 10% of that time, that's 7 hours a summer. Multiply by minimum wage and it only takes a summer and a half to meet the cost of a window AC unit. Which should last a long time if it's only used one month a year.
