There are a lot of misconceptions about the impact of air travel in climate change. The aviation contribution to global warming is hard to quantify, since there are key differences in the effect of each greenhouse gas dependent on the altitude at which it is emitted.
Air travel generates more polarized heated debate and misuse of facts than most other industries that produce greenhouse gases. In this diary I'll use recent news articles and statistics in an attempt to provide an objective summary of the current state of aviation emissions and possible future changes.
First a disclaimer, in case it matters to anyone. Due to a recent change of employment, my current work as a software engineer now includes some involvement with air traffic systems. I don't think it injects any bias into this diary.
However, there is clear bias in the quotes and soundbites reported in mainstream media. I discuss news from both the pro-industry and anti-industry extremes below - including an article where short haul flying is called immoral by one person, and favorably compared with driving a Toyota Prius by another! (You can probably guess which one of those comments was made by an airline CEO.) As usual, the media loves extremes but the truth is somewhere on a middle path.
Here's a quick review of some of the good and the bad in air travel.
Worldwide, aviation produces just 2% of GHG emissions. Good.
Aviation is one of the fastest-growing transport sectors. Bad.
Even in the air-saturated USA, aviation only emits 12% of transport CO2 and less than 5% of overall CO2 emissions. Good.
Aviation emissions can be worse than ground emissions (around twice to four times the impact, by some estimates) since they are released at altitude. Bad.
Despite high industry growth, engine and aircraft improvements have kept emission increases low. US carbon dioxide emissions from aviation remain roughly the same now as 15 years ago, while providing 70% more passenger miles. Passenger miles per gallon increased from around 30 mpg then to 50 mpg now. Good.
Aviation has fuel requirements (like high energy density and low freezing point) that mean it may be the last transport mode to completely eliminate fossil sources. Bad.
A common view within the industry is that aviation has been far more successful than other transport sectors at reducing per-passenger emissions, and is unfairly used as an easy target:
Airlines fear carbon message being lost
New Zealand Herald, 7 June 2007
The International Air Transport Association's AGM in Vancouver this week has been told that the public thinks air travel is a huge polluter of the environment and that the industry has been too slow to put the record straight.
The 600 delegates heard that aircraft fuel efficiency has improved 20 per cent in the last decade and nearly five per cent in the last two years. They were told air transport contributes only two per cent of global CO2 emissions, yet supports eight per cent of global activity. IATA's figures claim road generates 80 per cent of total transport emissions.
It says modern aircraft consume an average of 3.5 litres per 100 passenger kilometres, similar to a small compact car but with six times the speed. The next generation of aircraft, the Boeing 787 and Airbus 380 are targeting fuel efficiencies below three litres per 100 passenger kilometres. [Quick conversion: 3 litres per 100 km is about 80 miles per gallon - retrograde.]
Such a view is clearly not shared by all. The following protester typifies an increasingly common opinion of air travel:
Woman's sticky protest against air travel
ITV, 8 June 2007
A woman has superglued herself to the front doors of an online travel agency to protest against the "explosion" in air travel.
Penny Eastwood, 52, travelled all the way from Hebden Bridge in West Yorkshire to lastminute.com's headquarters in Victoria, London to call on the Government to do more to stop aviation pollution.
Ms Eastwood, who belongs to climate action group Plane Stupid, which focuses on aviation and short haul flights, pasted superglue over her hands and glued herself to the front doors of the building.
Ms Eastwood accused G8 leaders of spouting "hot air" - and lastminute.com of encouraging people to "binge-fly".
Most of the recent industry growth has been in low-cost short haul flights. Europe has seen much of it, and aircraft emissions are a hot topic there. This BBC article covers the European low-cost airline scene well:
Soaring future for cheap flights?
BBC, by Andrew Sinclair, 11 June 2007
If you want to know how the low-cost airlines have revolutionised the world of travel you need to go to Stansted airport. Ninety per cent of flights from here are with low-cost carriers - 23 million people passed through here last year.
...
Last week, Ryanair - Stansted's main low-cost airline - announced a 22% increase in passenger numbers to 42.5 million. Easyjet recently announced it is now carrying 16.5 million passengers a year - up 11%.
It is partly due to the growth in low-cost air travel, not just here but all around the world that carbon emissions from aircraft have risen by 111% in the past 15 years.
...
[T]he Right Reverend Tony Footit, former Bishop of Lynn and now environmental advisor to the Diocese of Norwich, has said we all need to think much more carefully about travel.
"I think it is immoral to fly within the United Kingdom or Western Europe when it perfectly possible to travel by train but it seems perfectly reasonable to fly to the United States or far east but we ought to really ration it and ask if the trip is really necessary," he said.
Although aircraft emissions are rising it is worth keeping this debate in perspective.
"Most people think airlines are all the same - they really are not" said Andy Harrison, chief executive of Easyjet. ... He said the main low-cost firms use modern, quieter aircraft, which emit far fewer emissions and are always very close to full.
"Last year we emitted 95.7 grams of carbon dioxide per passenger kilometre - that is less than the Toyota Prius," he said.
That's quite a range of opinion, from calling short haul flight immoral to comparing it with driving a Prius! I don't know the article's source for claiming a fifteen year 111% rise in aircraft carbon emissions, but it's possible it refers only to the UK or mistakenly equates an increase in passenger miles with a corresponding rise in emissions. It certainly doesn't match United States trends, as seen in the latest Environmental Protection Agency (EPA) statistics for CO2 emissions in transport:
US Transport CO2 Emissions (Tg CO2 Equiv.) |
Transport mode | 1990 | 2005 | 15yr change | % in 2005 |
|
Passenger cars | 615 | 615 | + 0% | 32% |
Light-duty trucks | 314 | 510 | + 63% | 27% |
Other trucks | 227 | 385 | + 69% | 20% |
Buses | 8 | 15 | + 82% | 1% |
Aircraft | 180 | 186 | + 3% | 10% |
Ships and boats | 47 | 64 | + 36% | 3% |
Locomotives | 38 | 50 | + 32% | 3% |
Other | 50 | 43 | - 13% | 2% |
|
TOTAL | 1479 | 1908 | + 29% | 100% |
|
International bunker fuels | 114 | 97 | - 15% | 5% |
Table notes:
- The "Light-duty trucks" category includes many SUV models.
- The "Other" category includes motorcycles, pipelines and lubricants.
- The "Aircraft" category shows emissions for domestic flights only.
- International air travel is part of the "International bunker fuels" category, which is not included in the total and covers civilian and military use for international transport: both aviation and shipping.
From the EPA stats, we can see that private vehicles (cars and light trucks) account for 60% of transport CO2 emissions and almost 20% of total CO2 emissions in the United States. Even pessimistically assuming most of the international bunker fuels category is international flight, it's clear that aviation is responsible for no more than 12-15% of transport CO2 emissions and 4-5% of total CO2 emissions. Furthermore, air travel emissions have not increased in fifteen years while the industry has provided many more passenger miles. The extra flights have been balanced by improved fuel efficiency.
If you're curious to know just how much extra American domestic air passenger traffic since 1990, here is the Air Transport Association data: from 1990 to 2005, passengers enplaned increased 59% and passenger miles increased 70%. The domestic passenger load factor (a measure of occupancy) was 60% in 1990, and 77% in 2005. Passenger miles per gallon are up from around 30 mpg in 1990, to almost 50 mpg today.
If we want to take a "biggest problems first" approach to emissions in the USA, it is clear that aviation is some way down the list below the clear big two: burning oil distillates in private road vehicles is number two, and burning coal for electricity is undisputably number one.
But I'm not writing this to defend the air travel industry against legitimate criticism, and there certainly is some.
- Aviation emissions are made worse by the altitude at which they are released.
- Oil will probably remain a primary component of jet fuel for years, perhaps even after we've managed a transition to zero-fossil-fuel road vehicles.
- Aircraft efficiency improvements are barely keeping pace with the growth in passenger miles.
- People are flying more for convenience and leisure.
- They are paying a financial price to fly that does not reflect the environmental cost.
Of course, this last point applies to all fossil fuel use, probably to coal-generated electricity and private vehicle use most of all.
To combat the impact of flight on climate change, many airlines and travel agencies now offer voluntary carbon offset schemes whereby passengers can pay an extra fee that will be used to reduce emissions elsewhere. In Europe, this may become a compulsory cost that airlines will need to absorb or pass on:
European Union Approves Carbon Trading For Airlines
Aero-News.Net, 10 June 2007
A controversial plan to require airlines to pay for the amount of carbon dioxide their aircraft put into the atmosphere won the approval of transport ministers in the European Union Saturday.
The measure -- aimed at cutting back to greenhouse gases -- requires approval by the European Parliament before it becomes law. If that happens, in less than four years airlines would be forced to either cut back on the amount of carbon dioxide produced, or purchase credits from other industries -- a practice known as carbon trading.
Airlines are opposed to the forced implementation of the plan, stating the carbon-capping scheme, to be imposed in 2011, would cost the industry over $5 billion annually -- while providing negligible benefits to the environment.
...
For the moment, the proposal includes only EU carriers. The United States has warned the EU that attempting to impose the plan on non-EU airlines could be a violation of international aviation rules.
A reasonable plan is met by opposition from the affected airlines, and a warning from the United States government. I would not expect anything else. But despite its opposition to this plan, the industry is continuing to make big reductions in fuel use (and hence emissions) per passenger mile. The progress is coming from many sources:
- more efficient engines
- lighter aircraft
- more direct routes
- fuller flights
- scheduling departures to reduce landing congestion at the destination
- more direct descents with less leveling
In the near future this list may include the use of biofuels. Here's one example of research into non-fossil aircraft fuel:
Greener Jet Fuel
Technology Review, by Emily Singer, 11 June 2007
The CEO of Amyris Biotechnologies says genetically engineered microorganisms could make better jet fuel.
...
But designing less-polluting new jet fuels is a challenge. Such a fuel must have a freezing point low enough to withstand high-altitude temperatures and an energy density high enough to allow planes to fly long routes without added weight--two requirements that take currently available biofuels out of the running.
...
A new biofuel under development by Amyris Biotechnologies, a startup based in Emeryville, CA, could fill that hole. ... Amyris scientists say they can now produce hydrocarbons with properties that rival the current jet-fuel industry standard, a kerosene-based product known as jet-A. The microbial factories ferment sugar to produce hydrocarbons, a process that has significantly less impact on global warming than traditional fuel production.
[Quotes from the CEO:]
Now we've been able to make it efficiently enough that we believe it would allow us to make a jet-A equivalent with better properties on energy and freezing point with a $40 barrel cost equivalent by 2010 or 2011.
We foresee selling our fuels as blends. ... I don't think we can deliver the volumes the world will need for transportation fuels in the short term, so we're creating fuels that can be blended.
Reducing greenhouse gas emissions is important in every use of energy. As in other sectors, the most important step for aviation will be to reduce our use rather than wait for technology to provide solutions. Companies can find alternatives to business air travel in many situations. People can take more non-flight vacations. They can purchase carbon offsets, from independently certified sellers. It also helps a lot to choose airlines that invest in modern fleets -- newer aircraft use less fuel.
Aviation is (despite the media hype) still a very minor producer of greenhouse gases, compared to the coal-fired plants and private vehicles that pollute the planet. But without progress, air travel may be left by default as the biggest emitter in the developed world if we are successful at transitioning to renewable energy for our cars and electricity.
Looking at the efficiency gains of the past and current research, I think air travel will get a lot cleaner. The most important question is the same for this industry as it is for the larger emitting sectors of electricity and road transportation. That question is:Will change come fast enough?