[taktoa]

The heat emitted by burning fossil fuels is completely irrelevant compared to the greenhouse impact. We burn about 11.7 gigatons of oil equivalent a year, which over 200 years would be 2.7 * 10^16 kWh. The greenhouse effect increase over the last 20 years leads to over 2.2 * 10^15 kWh/yr added to the planet, over 20x as much.