Cities tend to be darker and hotter than the surrounding countryside due to the buildings blocking the sunlight. The real reason behind global warming is that our world is becoming more urbanized; thus making more places darker and hotter (even if everyone was forced to use mass transit in every city and every town on Earth). We could make the cities (and the earth) cooler by re-wilding (transforming abandoned buildings into forests). Re-wilding efforts must also take future population growth into mind in addition to long-term regional economic growth patterns.