Southern "hot" cities more energy sustainable than northern "cold" cities?

[Bill in NC]

But for heating, heat pumps are MUCH more efficient than burning fuel (boiler or forced-air furnace)

Ca Bob wrote:
Since air conditioners are, in part, heat engines (they compress a gas, allow it to cool to about ambient, and then allow it to expand, which results in cooling), the overall efficiency of an air conditioner is relatively low.