Assuming a bedroom with surface area of 50 m^2 and an insulation R-value of 2 m^2K/W and an outside temperature of 30C, 300W would be required to keep the room at 18C. Cooling down 8 billion such bedrooms would require 24TW, which represents approximately a 10% increase in global power consumption.

Certainly a lot, but doesn't seem "catastrophic" and is realistic with today's technology.