Cool micro-climates are places where the air temperatures, humidity, radiant temperatures and wind speeds are more comfortable than surrounding areas. A city’s vegetative cover – especially shade trees – can simultaneously lower the cooling loads of buildings, air pollution and the temperatures of outdoor air, pavements and storm water runoff, while sequestering carbon and performing other tasks and services. Many cities have lost their forest cover. Trees breathe out what we breathe in; we breathe out what trees breathe in. According to Professor Brian Stone, the combination of albedo enhancement and reforestation “are the single most effective option available to cities to counteract the very real threats of CC during the next half century … none is more effective and less energy-intensive than planting trees.” The costs of trees are not trivial: increased water demand, pruning their branches, raking and removing their fallen leaves, and repairing rumpled sidewalks and root-invaded underground pipes. Humans cut down more trees than they replant. The global tree count is down to about three trillion from an estimated five to six trillion in prehistoric times. Trees have long been appreciated as urban amenities and oases. The earth needs trees. Humans need trees. Cities need trees.