UW Climate Action Plan

The University of Washington just released a draft Climate Action Plan. This post focuses on a small part of it: air travel, which the UW says (see graph on p9) is only 10% of emissions. I think they're probably off by a factor of 2. Here's why:

• The draft says (p. 30) that "air‐travel miles are estimated from costs using a constant conversion factor ($0.25/mile)". Details below on where this number comes from, but its iffiness can be seen from some simple estimates. San Francisco is about 700 miles from Seattle, so a 1400 mile round-trip at $0.25 per mile would total $350. (Orbitz is currently offering 5 direct flights for less than $200 each.) New York is about 2400 miles from Seattle, so a 4800 mile round-trip at $0.25 per mile would total $1200. (Orbitz is currently offering 5 direct flights for less than $400 each.)London is about 4800 miles from Seattle, so a 9600 mile round-trip at $0.25 per mile would total $2400. (Orbitz is currently offering 5 one-stop flights for less than $1400 each.) Beijing is about 5400 miles from Seattle, so a 10800 mile round-trip at $0.25 per mile would total $2700. (Orbitz is currently offering 5 one-stop flights for less than $1200 each.) PS. You can get travel distances from Wolfram Alpha!
  

So on that basis alone it seem reasonable to halve the cost/mile estimate, which would produce a doubling of the CO2 emissions from air travel.

We can also trace the history of the $0.25/mile number, and it's not encouraging:

• The number appears to come from the 2005 Inventory of Greenhouse Gases Ascribable to the University of Washington (also linked from here), which has this citation for the $.25/mile figure in a footnote on p33: "American College and University Presidents Climate Commitment, Implementation Guide, v. 1.0, September 2007, p. 15 (05-153)." The footnote goes on to say this: "The U.S. Bureau of Transportation Statistics maintains a national average revenue per passenger-mile, which was 12.22¢/passenger-mile in 2003, the most recent year available (see 05-098). However, the national figure is strongly influenced by budget and recreational travel that is atypical of the professional travel induced by a university."
• In turn the ACUPCC Implementation Guide (also linked from here) gives $0.25/mile, citing (on p. 15) "Huang, S. (2000). An Analysis of Air Passenger Average Trip Lengths and Fare Levels in US Domestic Markets. [Working Paper] Institute of Transportation Studies, University of California, Berkeley.
• As far as I can tell, that paper by Huang says nothing about 25 cents per mile. Where the 25 cents/mile figure comes from is a mystery to me.
• What the Huang paper does say is "For most coast-to-coast operations with trip lengths between 2200 and 2800 miles, the average cost per mile is only about 10 cents, since the fixed costs for these trip lengths ranges are a much smaller part of total costs." Indeed, looking at Huang's Figure 5 shows that for trips of 800+ miles (e.g., anything farther than San Francisco) the average cost is much closer to $0.15 than $0.25. An average cost-per-mile of $0.25 would have to feature a disproportionate number of short trips (of about 300 miles or less one-way) and this is almost certainly not a good estimate of UW professional travel.

Maybe a UW student can get a better estimate as a capstone project...