We all know that greenhouse gases (GHG) like carbon dioxide and methane can contribute to global warming, but we may be surprised which metropolitan area releases the most GHG. A recent study of emissions in 10 major global cities found Denver, Colorado had two to five times higher emissions than the others. The remaining nine cities finished in this order: Los Angeles, Toronto and Cape Town (tied for third), Bangkok, New York City, London, Prague, Geneva, and Barcelona.

Running parallel to these findings, a 2008 American Lung Association study of U.S. cities found that Pittsburgh, Pennsylvania leads the way in short-term levels of particle pollution. "Those particles are usually comprised of ash, soot, diesel exhaust, chemicals, metals and aerosols," explains Josh Peterson. "Breathing air like this can cause asthma, heart attacks, strokes and lung cancer." Rounding out the top ten of that particular study were: Los Angeles; Fresno/Madera, CA; Bakersfield, CA; Birmingham, AL; Logan, UT; Salt Lake City, UT; Sacramento, CA; Detroit, MI; and Baltimore, MD/Washington D.C

Besides steering clear of L.A., what can you do right now?
  1. Find Out Where Your Town Ranks: Check out the EPA's MyEnvironment page and/or the American Lung Association's State of the Air page.
  2. Don't Be a City Hater: Remember that although buildings account for an estimated 48% of all GHG emissions, the carbon footprint of the suburbs is even worse.
  3. Get on the Bus: As a first step to reduce your city's GHG emissions, become a public transportation user and advocate. See below.
Reasons to Use Public Transportation
  1. Use Transportation Daily: If one in 10 Americans used public transportation daily, it would result in a 40% reduction in U.S. reliance on foreign oil.
  2. Bus is Safer: Riding a bus is 79 times safer than riding in your own automobile
  3. Public Transportation Saves on Oil: Currently 855 million of gallons of oil (equal to 45 million barrels) are saved thanks to those people who are taking public transportation each year. (This is roughly the energy needed to power 25% of all American homes annually.)
  4. Reduction of Carbon Monoxide: If 20% of Americans rode public transportation daily, it would lead to a 20% reduction of carbon monoxide emissions.
  5. Interact More: You're way more likely to interact with your fellow human beings on a bus or train.