About 30,000 runners will invade Washington Oct. 28 for the 2012 Marine Corps Marathon. The race's popularity has skyrocketed since its inception in 1976, when 1,175 participants undertook the lung-busting challenge.
Nationwide, people are flocking to marathons: Between 2000 and 2009, the number of participants has increased 58 percent. This growing obsession with covering vast distances by foot has me thinking about its environmental efficiency compared to other modes of transit. How green are our two legs?
Calculating the average runner's greenhouse gas emissions for a 26.2-mile distance is a fairly straightforward task.
The first step is to determine how much energy is burned by the typical marathoner. Exercise physiologists estimate that an ordinary runner weighing 150 pounds uses approximately 3,000 calories on the marathon course. The next step is to determine how many carbon dioxide equivalents are released into the atmosphere in the creation of those calories.
You see, the carbon dioxide that a runner exhales does not directly contribute to climate change, because it's a part of a natural carbon cycle. Humans exhale carbon, plants inhale it, humans eat it and exhale it some more. However, our agricultural system uses fossil fuels to produce food, which means that carbon that had been safely stored in the ground is extracted and added to the atmosphere. Growing food on an American farm emits something like 0.0064 pounds of carbon dioxide equivalents for every calorie produced. (A carbon dioxide equivalent includes emission of both carbon dioxide and other greenhouse gases, such as methane and nitrous oxide.) That means a runner eating a standard American diet is responsible for the emission of 19.2 pounds of carbon dioxide during a marathon.
A few footnotes are in order. Statisticians include all the food that farmers produce when calculating greenhouse gas emissions per calorie. If we didn't throw away as much food as we do, exercising would be less carbon-intensive by this standard.
The efficiency of food distribution and production is out of your control, but you can change such things as your diet. A calorie from fruit and vegetables is responsible for about 40 percent less greenhouse gas than a meat or dairy calorie, so vegan runners do substantially better in this department than omnivores.
You could also slow down. While slower runners get less glory, the tortoises are a little bit greener than the hares. Running a marathon at a pace of 10 minutes per mile releases about 5 percent fewer carbon dioxide equivalents than running at six minutes per mile.
What if you ditched your running sneakers and hopped on a bicycle? Just like running, it depends somewhat on how fast you go, but overall, cyclists produce far less greenhouse gas than runners over the same distance. Pedaling at a moderate 13 mph, a 150-pound bicyclist would burn around 1,150 calories over 26.2 miles. Eating a standard American diet, he would be responsible for 7.4 pounds of carbon dioxide - 60 percent less than the runner generated.
You might be surprised at how these totals compare to driving. The EPA estimates that the average vehicle on American roads emits 0.87 pounds of carbon dioxide per mile. So, over 26.2 miles, a car would account for just 22.8 pounds of greenhouse gas - about 19 percent more than the runner.
Of course, it's not entirely fair to suggest that your sedan is only slightly less environmentally friendly than your all-natural body. The carbon footprint of a car is more significant than the gas that it burns. When you take into account raw materials, manufacturing and disposal, in addition to fuel, a car is responsible for about 1.1 pounds of carbon dioxide equivalents per mile, meaning that it's true marathon footprint is closer to 28.8 pounds, or 50 percent more than running.
Some analysts have pointed out that even that estimate is low, as nationwide infrastructure required to support automobile transport - including road-building and maintenance, gas stations, etc. - is difficult to calculate.
Bicycles, too, have impacts beyond the food required by their riders. Manufacturing the average bicycle accounts for approximately 530 pounds of carbon dioxide. It's difficult to apportion that total on a per-mile basis, though. Some people keep the same bicycle for an adult lifetime, while others change every time the color goes out of style. In addition, if you use a bicycle for commuting in addition to leisure riding, the carbon you save by not driving quickly pays for the manufacturing emissions.
By riding about 400 miles instead of driving, a bike pays for itself, environmentally speaking.
And running shoes, too, have environmental impacts, although they don't compare to those of a car or bicycle. A conventional leather sneaker is responsible for 16.6 pounds of carbon-dioxide equivalents after taking into account manufacture, transport and disposal. Many marathon runners change shoes every 500 miles, which means the shoe itself would be responsible for an additional 0.9 pounds of greenhouse gas during a marathon run.
Get the scoop!
Even a runner leaves a carbon footprint
-
-
Kebabs: Health kick on a stick
Grilling is a simple way to feed your family well this summer. Start with a lean meat and a healthful marinade and then allow the grill to strip away additional fat for a heart-healthy and waist-friendly final result. Plus, grilling caramelizes the natural sugars in foods, which adds flavor without additional calories and fat.
-
Boy Scouts: Yes to gay youths, no to adults
The Boy Scouts of America on Thursday ended its ban on openly gay youths but maintained a prohibition on gay adult leaders, a decision framed as a compromise but one that could lead to litigation and thousands of defections from one of America's largest youth organizations.
-
Twitter introduces website security tool after AP account hacked
Twitter is adding a new security tool to its website, making it harder for outsiders to gain access to accounts, a month after a false posting triggered a stock-market decline.
-
Mayor wants tornado shelters in new homes
Moore Mayor Glenn Lewis wants tornado shelters in all new homes in his city, where an EF-5 tornado damaged or destroyed more than 12,500 homes Monday afternoon. A proposed ordinance would require a shelter inside or outside each new residence.
-
TIMELAPSE: Take a tour through the damage in Moore
Take a driving tour of the damage in Moore caused by Monday's tornado.
-
AUDIO: Residents share their tornado experiences
Moore, Okla., residents talk about living through Monday's EF-5 tornado.
-
Mom delivered baby as tornado struck
Shayla Taylor was so far along in labor that her nurses at Moore Medical Center decided not to move her when Monday's tornado hit. They waited out the storm in an operating room, where the wall disappeared as the tornado hit the building.
-
In fan fiction, your favorite characters do what you want them to
When J.J. Abrams took over the "Star Trek" franchise in 2009, he boldly went where the series hadn't gone before — romantically — pairing Uhura with Spock. Many fans disliked the change. Some loved it. Others didn't care, because they just wanted to see Kirk and Spock make out.
-
VIDEO: Orlando shootout tied to Boston bomb suspect
The FBI says it was involved in a fatal shooting near Universal Studios in Orlando, Fla. CBS News senior correspondent John Miller reports that the victim was a friend of Tamerlan Tsarnaev, the older brother suspected in the Boston Marathon bombing.
-
Okla. officials vow not to quit looking until everyone is found
The tornado that killed 24 people and injured at least 100 others in the Moore and Oklahoma City area cut a 17-mile-long path that started in Newcastle and ended at Lake Stanley Draper. Nine of the dead are children.
-
Where to get the best deal on beer, haircuts, movies
Looking for a good deal on a six-pack of beer? Try Charlotte. A haircut that won't burn a hole in your wallet? Harlingen, Texas, is your best bet. A trip to the movies? Hilo, Hawaii, is supposed to be nice this time of year.
-
Okla. front pages capture tornado aftermath
View how several Oklahoma newspapers covered Monday's massive tornado in Moore. Please note that officials revised the death toll downward early Tuesday morning after some papers were printed, but it is expected to climb again as recovery efforts continue.
-
Photos: Aftermath of massive tornado in Moore
Storm victims were pulled from the rubble and residents began surveying the damage late Monday and early Tuesday in the Oklahoma City suburb of Moore, where a powerful tornado destroyed entire neighborhoods and left dozens dead.
-
VIDEO: Pres. Obama's remarks on the Okla. tornado
President Obama speaks on Monday's deadly Okla. tornado.
-
VIDEO: Tornado survivor's missing dog found during TV interview
Barbara Garcia was being interviewed by CBS News about how she survived the destruction of her home to Monday's massive tornado in Moore, when the dog she feared dead was suddenly discovered alive in the rubble of her home.
- More Get the scoop! Headlines
-
Officials: Tsarnaev Friend Linked to Slaying
Obama:Sexual Assault Threatens Trust in Military
Bridge Collapse Survivor: 'Rough Day'
Jersey Shore Open for Business
Raw: Memorial Day Flags Placed at Arlington
New Wheelchair Lift Promises More Access
First Person: Mom Discusses Famous Tornado Photo
Raw Video: Washington State Bridge Collapse
Boy Scouts Approve Plan to Accept Gay Boys
Officials: Truck Hit Bridge Before Collapse
Sheriff: No Sign Killing of 2 Kids Was Planned
Obama Defends Drone Strikes, With Limits
Raw: Jurors Deadlock on Jodi Arias Penalty
Boy Scouts Decision "First Step" Say Activists
Raw: Utah Teen Arrested in Death of His Brothers
Closer Look at Okla. School Where Children Died
Two Suspects in Murder Known to London Police
"Be Ready": NOAA Warns of Busy Hurricane Season
SeaWorld: Penguins Are Coolest Thing in Florida
