With gas prices breaking new records every day I am wondering, is it better for the environment to fly or drive to my summer vacation?
In terms of greenhouse gas emissions, the quick answer is that driving is far better than flying. But let's see why that is.
According to the Greenhouse Gas Protocol, the internationally accepted process for quantifying greenhouse gas emissions, the emissions from a long-haul (less than 1,000 miles) flight are 180 grams per passenger mile. So a nonstop flight from San Francisco to Boston would create 487 kilograms of carbon dioxide emissions per person (2,708 miles x 180 g/passenger mile), or almost 1 ton for a round-trip. For a family of three, the "carbon footprint" of your vacation would already be almost 3 tons! Generally, larger airplanes are more efficient per mile, so short-haul flights release even more emissions.
But according to the International Panel on Climate Change, these numbers are only for CO2 emissions and don't take into account the additional greenhouse gas emissions (methane and nitrous oxide), water vapor, and the increased effects from releasing all of these at such a high altitude. We therefore need to apply a "radiative forcing index" of 2.7 to correct for this, bringing your family's emissions to over 8 tons.
Now, let's say that your family decided to take your medium-sized (defined as having a 1.4-to-2.1-liter engine) family car, such as a Toyota Corolla, on that same trip. Sure it would take you a lot longer to get there, but think of all the national parks you could visit on the way! Again, according to the Greenhouse Gas Protocol, your emissions would be 300 grams per mile (equivalent to a 30-mpg vehicle). Since you can't drive a straight line all the way across the country, the trip is going to be about 3,100 miles, releasing 930 kg of greenhouse gases, or less than 2 tons for the round-trip. Unlike for flight emissions, the vehicle's emissions are not measured on a per-occupant basis, so you would release one-quarter less by driving across the country on your vacation.
If that is not enough incentive, think about the cost. Last week, the cheapest San Francisco-Boston round-trip flight I could find was $445 per person, or $1,335 for the family. Now that United Airlines has cut a fifth of its fleet, prices on all airlines are even higher. To drive your 30-mpg Toyota across the country you would need 207 gallons of gasoline; at today's average price of around $4 per gallon you are looking at a gas bill of $828, more than enough savings to pay for campgrounds on your cross-country drive.
Let's take a quick look at some other alternatives. The emissions from taking a passenger train (Amtrak) are roughly comparable to those from driving (310 g/passenger mile), but these emissions are per passenger. This adds up to almost 6 tons for the three-person family -- less than flying, but a lot more than driving. Unfortunately, it would also take longer and cost more than both driving and flying.
No matter which form of transport you use, you can always mitigate your climate impact by purchasing high-quality, verified offset credits through nonprofit organizations that fund energy-efficiency improvements, such as LiveNeutral, or provide energy-saving compact fluorescent light bulbs to low-income families, such as LiveCooler.
But are you sure you really have to travel? Consider taking what is being called a "staycation." Visit your local museums, go camping at a local state or national park, or stay at a local bed-and-breakfast. Not only will you have a relaxing escape from your daily routine, but you will also support your local economy and reduce your impact on the environment.
Whatever you do, enjoy your summer!