"It also worth noting that in 1790, Sydney (population 1,715) was still surrounded by mostly natural bushland, where modern day Observatory Hill in Sydney (population 4,627,000) is now surrounded by the concrete, steel and glass of a modern city, not to mention the tens of thousands of air-conditioners pumping out hot air into the surrounding streets, nor the 160,000 cars & trucks that cross the Sydney Harbor Bridge daily and pass within 100 meters of Observatory Hill."
Nice example from Piers how humans warm the planet.
