Greenhouse gas emissions from domestic commercial aviation have fallen 13 percent between 2000 and 2006, according to recently released figures from the Environmental Protection Agency. I blogged about a USA Today article on this report last week, and I finally tracked down the original, cleverly obscured on the EPA website. (The aviation-relevant sections are here and here.) The pattern of greenhouse gas emissions from aviation mirrors consumption of fuel. Carbon dioxide is by far the most common greenhouse gas to be emitted, although relatively small amounts of methane are emitted , especially during takeoff and landing, along with nitrous oxides. (Newer engines have to comply with EPA rules limiting nitrous oxide emissions.)
The relationship between jet fuel consumption and all aviation emissions (including general aviation and military flights) is even more closely mirrored.
But did emissions fall just because of the 2000-2001 recession and September 11, both of which did a number on the airline industry? That is not clear. As the chart below shows, with the exception of a post-9/11 slump, passenger totals grew even as emissions declined:
This means that U.S. airlines have done a better job of transporting passengers on less fuel. This includes harmonizing schedules, increasing load factors, switching to more fuel efficient aircraft and engines, and generally undertaking fuel-saving measures. (Alaska Airlines, for example, bought lighter aluminum beverage carts to replace their steel ones.) The FAA also takes some credit for the drop in emissions, including the introduction of Reduced Vertical Separation Minimum and Continuous Descent Arrival, and it promises even greater gains with the NextGen program to transform air traffic control and allow planes to fly more direct routes.
It also shows that increasing the cost of fuel will force airlines to do with less of it. The several-times-over run-up in oil prices since 2000 has functioned like a de facto carbon tax, albeit one that does not generate government revenue or necessarily lead to investments in alternative energy or climate change mitigation.
I’m not convinced that we are close to “carbon-neutral” growth, as FAA associate administrator Daniel Elwell said recently. He is attributing a lot of the projected efficiency gains to NextGen, which is way behind schedule and way over budget. But all the same, I’m pleased and impressed with the U.S. performance in reducing its aviation-related greenhouse gas emissions.
From here, I turn it over to commentators who are better-versed in climate change and environmental policy.
Evan Sparks's Aviation Policy Blog 
[…] cleaned up its act like few other sectors in recent years, but it still can’t catch a break. Earlier this month, […]
Hmm. Interesting. Thanks for hunting that report down.
I wrote something about this a while ago:
http://www.foreignpolicy.com/story/cms.php?story_id=4137
w/o benefit of numbers 😉
Just eyeing the report, I see a couple points:
International fuel usage: I think we’re all in agreement that the airlines are cutting back on domestic service to focus on international service. How much is international fuel usage included in the totals? Table 3.5 shows that increase from 58.7 in 2001 to 71.1 in 2006.
Military numbers: How much is also a decline in domestic military usage — is that included in the number. I suspect the air force is cutting back on usage as forces move overseas and also training flight decline (maybe?)
SAGE model: how good is the FAA’s SAGE model for this sort of stuff?
Regional Jets: Increase/decrease in RJ would move the numbers — and given the numbers of RJs in operation — that move might be huge.
My final two cents: OK, a bit more fuel efficiency and mostly reflecting cuts in domestic service.
Krishna — You’re absolutely right about the international expansion as a proportion of flights. The trouble is how to measure it. See section 3-11 of the “Energy” chapter for more on this. “Activity data on aircraft fuel consumption were collected from three government agencies. Jet fuel consumed by U.S. flag air carriers for international flight segments was supplied by the Bureau of Transportation Statistics (DOT 1991 through 2006). It was assumed that 50 percent of the fuel used by U.S. flagged carriers for international flights⎯both departing and arriving in the United States⎯was purchased domestically for flights departing from the United States. In other words, only one-half of the total annual fuel consumption estimate was used in the calculations. Data on jet fuel expenditures by foreign flagged carriers departing U.S. airports was taken from unpublished data collected by the Bureau of Economic Analysis (BEA) under the U.S. Department of Commerce (BEA 1991 through 2006).”
Thanks for reading!
Evan: thanks.
from 3-8 of the energy section:
“CO2 from the
domestic operation of commercial aircraft increased by 4 percent (5.4 Tg) from 1990 to 2006, well below the
growth in travel activity (passenger miles traveled grew by 69 percent from 1990 to 2005, the most recent year of
available data). The operational efficiency of commercial aircraft improved substantially because of a growing
percentage of seats occupied per flight, improvements in the fuel efficiency of new aircraft, and the accelerated
retirement of older, less fuel efficient aircraft. Across all categories of aviation9, CO2 emissions decreased by
approximately 5.2 percent (9.4 Tg CO2) between 1990 and 2006. This decline reflects a 56 percent decrease in
emissions from domestic military operations, which more than offset a small increase in domestic commercial and
general aviation emissions. For further information on all greenhouse gas emissions from transportation sources,
please refer to Table A-108 in Annex 3.2.
And I’m not sure those numbers are even including the international sales….see table 3-5.
The point about fuel prices working like a de-facto carbon tax without the benefit of an agency collecting the revenues to make improvements is dead on. If fuel prices hadn’t been kept artificially low (and I say artificially because, just like auto drivers, airlines & their passengers are not paying the full social cost of flying jets around), airlines could have learned to manage their operations in a financially solvent manner while government agencies could have more money to invest in fuel savings methods like CDAs, electrified gate power at all airports, etc. Now the prices are just high and the government isn’t getting new revenue to make improvements.
My suggestion to the government — step in and use these high fuel prices to help bring reality to the aviation system. The government should closely monitor fuel prices, and should they drop, that is the time to act with carbon or other fuel taxes.
Krishna, great point about SAGE. If you have access to academic journals there are some articles written about it. They can model at the flight level, and take trajectory inputs. http://www.faa.gov/about/office_org/headquarters_offices/aep/models/sage/media/FAA-EE-2005-02__SAGE-Inventory_Report-Text.pdf