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Walking: Still Better Than Driving

walking.jpg Walking is 12 times better for the climate than driving.

In case you missed it, there was a bit of a kerfuffle in the blogosphere a few months back, concerning the climate impacts of walking vs. driving.  Apparently, some folks -- New York Times columnist and blogger John Tierney in particular -- were spreading the claim that a pleasant stroll to the store might actually release more GHGs than getting behind the wheel.  Other bloggers picked up the meme, including one post with the headline:  "Be Green:  Drive."

The idea may sound absurd, but there's a legitimate insight behind it.  Walking burns calories, which come from food -- and it takes an enormous quantity of fossil fuels to produce, process, and transport everything that we eat.  Add in the other GHGs from agriculture -- everything from cow manure to emissions from synthetic fertilizers -- and you've got a potent global warming cocktail in every glass of milk.

But our doppelgangers at the Pacific Institute did their homework, compiling evidence about climate emissions from both cars and food.  And they came to the conclusion that walking emits about one-quarter the GHGs of driving -- earning a partial retraction from Tierney.  (You go, PacInst!)

But looking at the numbers, I think that the Pacific Institute's numbers are conservative. In fact, I think that when I take a short walk, I'm being at least 12 times as friendly to the climate as if I drove.  Your mileage may vary, of course; but my shoes get about 220 miles per gallon.

Here are a handful of reasons why I think that walking look even more climate friendly than the Pacific Institute's estimates suggest:

What would a walker be doing otherwise? 

Walking burns calories, but a person also burns calories while driving, or just loafing around.  So what matters isn't the totalcalories your body burns during a walk, but the marginal calories from walking vs. driving + whatever else you'd do with your time.  CalorieLab gives some helpful clues:  for a half-hour walking trip, they estimate that a 176 pound person (the average of the median weights for men and women in the US) burns about 106 extra food calories, compared with a 5 minute drive and 25 minutes of watching TV.  This figure is slightly less than the figure the Pacific Institute used.  And if you do anything more strenuous than sit on your butt for those 25 minutes, then the food-calorie "advantage" of driving narrows even further.

Score one for walking.

Where do the extra food calories come from?
If the calories to power your walk come from your waistline, then there’s no marginal food consumed -- and, potentially, a long-term climate gain, since it actually takes extra food calories to maintain a heavier frame. More likely, though, you’ll find a way to eat an extra bite or two of food in the day or so after your walk; the body seems to work overtime to maintain a set-point for weight. 

But if you're like me, that food could well come from “plate waste” -- food that would otherwise be thrown out.  (My marginal food calories tend to come from my kids’ leftovers. Who wouldn't want a scrap of cold, half-eaten bagel in the morning? I'm lovin' it!) Generally speaking, there’s plenty of waste in the food system:  USDA estimates that the US food system produces 3900 calories per person each day, of which roughly a third is simply thrown away or allowed to spoil.  (This paper, cites a figure of 3,774 calories per day, after accounting for net exports -- but who's counting?)

Any of your calorie needs that come from your waist, or your waste, are essentially climate neutral.  Score another one for walking.

What kind of food is it, anyway?

food CO2 intensityAs the food chart to the right shows (see here for the source, and here for a discussion), some foods have a major climate impact, while others are comparatively benign.  But my "marginal calories" -- the sorts of things I eat when I load up on when I'm hungry and my willpower is low -- are starchy, sweet, and/or loaded with vegetable oils. Those are the itty-bitty pink and red lines on the chart to the right, the ones with the smallest climate impacts.

So if you, like me, replenish yourself from a walk with starches or sweets, you may be doing your body no great favors -- but, yet again, the climate impact of your walk falls a bit. Score yet another point for walking.

What about cars?
The Pacific Institute's figures exclude life-cycle emissions related to manufacturing and maintaining your car.  This EPA study (see table 14) suggests that vehicle manufacturing alone increases the net climate impact of driving by at least 12 percent.

The final score:  Walking vs. Driving
Obviously, most of the points above are a bit mushy; but I think it’s
possible to give some ballpark estimates:

  • For walking energy itself, cut the Pacific Institute's emissions estimates by about 5 percent.
  • Accounting for food that would otherwise be waste, cut their estimates by another third.
  • For marginal vs. average food sources, cut food emissions by another third.
  • For vehicle manufacturing, increase car emissions by about 12 percent

This is all ballpark, back-of-the-envelope calculation, of course.  But if it's close to being right, walking is about 12 times better for the climate than driving.  In fact, a car has to get the equivalent of about 220 miles per gallon before it matches the fuel economy of shoe leather.

So until I can buy a car that uses a quarter of the gas of a Honda Insight, I'm going to keep on walking.

[Walking image courtesy of Flickr user rogiro, distributed under a Creative Commons license.]

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Comments

The "food CO2 intensity" chart isn't displaying


Posted by: Daniel Haran on 18 Jun 08

Very interesting article. I am a big fan of unconventional thinking like this. What if a car had less of an impact than walking? Most people would never entertain the idea, let alone research it so thoroughly.

In 15 or 20 years I think we'll need to re-evaluate this question. Although, fundamentally. walking just seems more natural.


Posted by: Nimic on 18 Jun 08

Holy crap. This is green overkill if I ever saw it. No wonder people are freaking out from eco-anxiety and enviros are losing some ground. Of course walking is better than driving. Are you kidding me? Does this even deserve analysis? How about concentrating on the need for more trails and access for walkers and cyclists, etc. Rock on.
- GM.


Posted by: greenmullet on 18 Jun 08

It sounds like another example of FUD from the oil lobby. The sort of tactic the auditors of reality might come up with after reading a Terry Pratchett novel.

Nicely fielded, Pacific Institute (and you, Clark ;-)


Posted by: Tony Fisk on 18 Jun 08

12 times sounds pretty close considering you're moving about 12 times as much weight around (100kg vs 1200 kg)


Posted by: Pierre on 18 Jun 08

Excellent points, Clark. I would also underline that eating local, organic food from lower on the food chain will also do a great deal to improve one's walking:gasoline efficiency.

Cheers from Charlottesville,

Lyle


Posted by: Lyle Solla-Yates on 19 Jun 08

greenmullet...

i agree, completely. this is not only insane, it is inane.

the modern mind has turned on itself, evident in this sort of completely nonsensical analysis.

it's isolated thought, to even think for longer than a second, to compare walking versus driving...

isolation of design, thought, and analysis is part of what is destroying the world.

and it leaves one without common sense, actually having to waste time on this stuff. i can only imagine the smiles coming from the coal side...


Posted by: JoshS on 19 Jun 08

On the surface it seems absurd to analyze it, but how much of common sense is also wrong? Some of you may have caught the article on the NY Times about food miles:
http://www.nytimes.com/2007/08/06/opinion/06mcwilliams.html

A quick pull quote: "lamb raised on New Zealand’s clover-choked pastures and shipped 11,000 miles by boat to Britain produced 1,520 pounds of carbon dioxide emissions per ton while British lamb produced 6,280 pounds of carbon dioxide per ton, in part because poorer British pastures force farmers to use feed."

In this case, locally raised food is actually worse for the environment. Everything is worth examining.


Posted by: Chris L on 19 Jun 08

In 15 or 20 years I think we'll need to re-evaluate this question.

This means we need to work on the climate impart of agriculture as well.


Posted by: mark on 19 Jun 08

So then we should examine the statement that, "everything is worth examining"? :)

My point is directed to the larger pattern of thought. It's nonsensical to compare consequences at the level for at least a few reasons.

But separately, I'd bet there are British farmers using methods with lower carbon impacts, than those measured by the study. And that's the central problem with such studies. They are photographs, usually very blurry and broad-brush ones at that, of a specific type of practice, isolated, compared against other isolated practices.

There's a diversity of ways to, say, grow corn or other food crops, just as there exist a diversity of related species or sub-populations.

To merely state, it's better to raise lamb in NZ rather than GB on the basis of that evidence is an isolated conclusion, outside of reality. It just doesn't make sense, when applied to a larger pattern and science-based context.

It's no different than some of Friedman's recent announcements about local versus distant agriculture....

It's evident of the broken current thinking on "Sustainability", especially that which starts using modern economic perspectives, like marginal costs, etc...


Posted by: JoshS on 20 Jun 08



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