Not only is the entire world experiencing a rise in temperatures, but cities may be exceptionally prone to the increasing heat. The 'urban heat island' is a term used to describe the higher temperatures usually seen within large cities compared to suburban and outlying areas. "[I]f [global warming] continues, if the planet heats up 4 degrees in the coming decades, cities will heat up a blistering 8 degrees," says NPR's Richard Harris.
So what's adding to the heat island? "Cutting down trees is a big factor," finds Harris. "Pavement also stores heat during the day and makes cities hotter at night. And as cities heat up, air conditioners run harder. Their exhaust heat also pushes up the temperature."
"Trees can help more than anything else, both by providing shade and by evaporating water through their leaves," says Harris. Greg Levine, with the non-profit Trees Atlanta, says a thick canopy of trees can easily drop air temperature by 20 or 30 degrees, compared with a paved parking lot. Yet, even in Atlanta, it would take "millions" of trees to combat that city's heat island.