Who is greener? Well, that depends...

As originally published on AskPatty.com. Here's the excerpt...

This week I happened to chance upon two situations of people debating their relative environmental impacts, with each side thinking she is more eco-friendly. In both cases, one party owns a more efficient vehicle while the other insists she lives a lower impact lifestyle overall despite having a less efficient vehicle.

So in this post, I will compare the vehicle usage patterns of two drivers – one a hybrid owner (Driver A), and one an SUV owner (Driver B). At first glance, A appears more environmental because she drives a hybrid, but let’s verify whether this is true with some numbers based on these two drivers’ actual life styles.

	Driver A	Driver B
Vehicle owned	Hybrid Toyota Prius	SUV Dodge Durango
Vehicle spec	2006 4 cyl, 1.5L	2006 4WD 8 cyl, 4.7 L, Auto(5)
Vehicle MPG (City/Hwy)	60/51	12/17
EPA Air Pollution Index* (0-Worst, 10-Best)	8	1
Daily commute (each way)	60 miles, highway	6 miles, town

* The EPA Air Pollution score represents the amount of health-damaging and smog-forming airborne pollutants the vehicle emits. This score does not include emissions of greenhouse gases.

This translates to an annual commute impact of…

	Driver A	Driver B	Difference (A minus B)
Miles driven per year	30,000 miles	3,000 miles	27,000 miles
Annual fuel use*	541 gallons	187 gallons	354 gallons
Annual fuel cost	$1623	$561	$1062
Annual CO2 Emission**	10,584 lbs	3,669 lbs	6,915 lbs

Assumes 250 working days , gasoline at $3/gallon. Sources:
* http://www.fueleconomy.gov/feg/findacar.htm
** http://www.terrapass.com/road/carboncalc.php

Driver A (hybrid owner) actually generates 6,915lbs more of CO2 than Driver B (SUV owner)! The clearest lesson to be taken from this is that simply living close to work can be a major environmental gain. Even though buying a hybrid electric car is a great thing, it doesn’t necessarily make you environmentally responsible in the big picture. In this real life case if you look at the bigger picture there’s an even wider discrepancy between these two drivers since Driver B is close enough to walk to work twice a week (cutting back emissions and gasoline by another 40%), while driver A lives by himself in a large house that takes a lot of energy to heat.

To truly understand one’s impact on the environment, accounting for the bigger picture of your daily car usage pattern and lifestyle is important. Accounting is usually valued only as a monetary cost, but for true comparison, we need to factor in economic costs too – which would take into account the opportunity cost of the next best alternative, and the externality cost to society and environment. Be aware too, that although carbon accounting is important, it is not the only story. Other greenhouse gases (e.g. methane, N2O) contribute to climate change too. Pollution from cars contributes to smog and health problems, not to mention odor nuisance and noise pollution. One’s lifestyle determines one’s eco-footprint – how many planets worth of resources are needed to support human race if everyone consumes at the same rate as us. I will explore eco-footprint in a future post.

Each of us makes choices based on our own very unique needs, budget, and preferences. Sure, a Hummer is downright excessive when you look at its environmental impact. But what about the more-efficient-than-a-Hummer, but still less-efficient-than-a-sedan SUV or pickup truck? In some cases, they may actually make sense to own! An outdoor enthusiast with a lot of equipment who needs to drive regularly to the ski resort on a mountain may need an SUV. A renovating homeowner who is doing regular hardware store run to pickup lumbers and other large-sized supplies need a pickup truck. It is simply too cost ineffective to pay Home Depot to deliver several times a month…

So in my opinion, simply being aware of the impact of one’s action on the environment is a good start. From there, the next step is to evaluate alternatives on how to do better, if you can afford to do so, and if not, when you can start doing better. Sometimes it is as simple as paying an extra $5K for the Honda Civic hybrid. Other times, it is a toss-up between your conscience and a roomier SUV because you make a lot of trips with 4 other passengers. Perhaps the decision to buy a smaller or more efficient car will have to wait in certain situations, e.g. till the kids go away to college. The key is to constantly evaluate your personal situation and make the most responsible decision you can, based on your own unique situation. If however, you do not yet own a car or is currently ready to switch, the best decision is to buy the most efficient car you can possibly afford, because once you go down the path of owning a particular vehicle, the switching cost will become another limiting factor.

The next time a friend challenges your automobile choice or transportation options, show them the tables above, and have a discussion about the bigger picture of both your commute pattern and lifestyle choices. The answer is usually a lot fuzzier than just choosing a more efficient car.

In summary, to all car owners out there – please do enjoy your vehicle, but please do actively consider the impact of your driving pattern and vehicle usage on the environment. You can be green by actively thinking about what else you can do to negate the carbon/GHG impact of daily vehicular usage. Here’s an inspiring example from Hewlett Packard 2006 Global Citizenship Report: "We estimate that for our monochrome LaserJet products, the total energy consumption saved since 1993 from use of [instant-on fusing] represents 4.1 million tonnes of carbon dioxide (CO2), equivalent to removing 870,000 cars from the road for one year.”

Remember, we can all be our own “power of one”. What’s the one change that you can make today to offset your carbon footprint?