The argument is that you aren’t moving additional energy into the city from power stations to run the AC, which ends up as heat. Instead you’re using energy that’s already radiated into the city from the sky.
As others have pointed out, you might do better bouncing the incoming radiation back out of the city with white roofs. And still others say you can do a bit of both.
Also, you could definitely do well to reduce your roof albedo by switching to white/reflective roofs. This point has been made endlessly over the last 30-40 years. No one actually does it. People are actually installing solar panels.
As others have pointed out, you might do better bouncing the incoming radiation back out of the city with white roofs. And still others say you can do a bit of both.