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Air Travel and the Environment

July 21, 2017

A NEW STUDY from Columbia University highlights some of the challenges to be faced by airlines in the coming years as climate change causes temperatures to rise. The report, by doctoral student Ethan Coffel and climatologist Radley Horton was published in the journal Climatic Change. It estimates that up 30 percent of commercial flights will face payload restrictions as heat waves and extreme temperature events become more common. The report comes only a few weeks after a severe heat wave caused the grounding of dozens of flights in the American southwest.

Extreme heat affects planes in different ways. First, there are aerodynamic repercussions. Hotter air is less dense than cooler air, so a wing produces less lift. This is compounded by reduced engine output. Jet engines don’t like low-density air either, and don’t perform as well in hot weather. Together, this means higher takeoff and landing speeds — which, in turn, increases the amount of required runway. Rates of climb are also impeded. Performance parameters require that a plane be able to climb away safely following an engine failure, and this might not be possible. Engines also are subject to internal temperature limits — exhaust gas temperatures, etc. — beyond which operation isn’t permitted. When it’s really hot outside these limits are easier to exceed.

Then you’ve got the simpler, more tangible effects: overheating electronics, increased brake temperatures, cabin cooling issues, and so on. Airplanes have a lot of internal machinery, and much of it runs hot to begin with. Throw in triple-digit temperatures, and things begin to break down. And let’s not forget the effects on ground support equipment and, of course, the people working outside.

Payload penalties are fairly common during hot weather, whereby a plane isn’t able to accept a full load of passengers or cargo. Restrictions will vary with the temperature, runway length, and other factors. Outright grounding of flights is rare, but at a certain point there isn’t much choice. You could say there are hard and soft limits. The aerodynamic limits are soft. That is, you don’t know for sure if a flight can safely depart, or at what weight, until you juggle the numbers. In other cases there are absolute temperature maximums, set by the manufacturer, that you’re not allowed to exceed. These can be component-specific, or can apply to an airplane outright. (We get a detailed paper printout before each departure that factors in weight, weather, runway length, and so forth. Usually this arrives jut before pushback, via cockpit datalink, and includes the takeoff speeds that we’ll use, the necessary thrust and flap settings, etc. The calculations that produce these numbers rely on published performance charts. Sometimes, above certain temperatures, data simply doesn’t exist. In that case, taking off isn’t an option.)

June’s heat wave wasn’t the first time flights have canceled because of heat, and you can expect it to happen more frequently. And this will be a regional thing. Certain areas of the world, and in turn certain airlines and air travel markets, are going to be harder hit than others. It won’t be a challenge as much for New York or San Francisco or Paris, as it will be for, say, Delhi or Dubai, where summertime temperatures already are extreme. It’ll be interesting to see how this impacts the Gulf carriers — Etihad, Qatar Airways, and Emirates — whose hub airports are located in one the world’s hottest regions. Fortunately for them, many of their long-haul flights arrive and depart in the dead of night, when it’s marginally cooler, but they have much to lose if summer temperatures, which already top a hundred degrees routinely, begin getting warmer.

This issue hasn’t been much in the forefront of Boeing’s or Airbus’s thinking, but the world’s plane-makers will have little choice but to design aircraft with better hot-weather performance. It’s a challenge that can be met — albeit one that we shouldn’t have gotten ourselves into in the first place, but that’s another conversation. One big problem, though, is that it takes a long time — the better part of a decade — to design, develop, and produce a new commercial plane. As for existing aircraft, there’s not a lot that can be done. You can’t just slap new wings or new engines onto a plane.

So here we are. This is another way in which we’re ill prepared for the coming challenges of climate change. And unfortunately, commercial air travel is a such a vital part of our society, and such huge economic driver; the bottom line repercussions for airlines could be in the tens of billions annually.

And we haven’t even touched on the ways climate change is going to intensify wind patterns, storms, and turbulence.

Last spring, a paper published a scientist from the University of Reading suggests that instances of strong, potentially dangerous turbulence will increase significantly by the middle of the century. The study was an expansion of an earlier, 2013 analysis of wind patterns in a busy section of North Atlantic airspace between the U.S. and Europe. That analysis showed a marked increase in both the severity and frequency of all grades of turbulence, from “light” through “severe.” You can read more details here. I’ve been flying across the North Atlantic since 1997. My observations are just that, and are purely anecdotal, but what I’ve experienced more or less meshes with the research. It’s become bumpier and windier, on average, and storms seem to be larger and more widespread. Most notably, it’s no longer uncommon to encounter thunderstorms even in the colder months.

Pilots will also face an increase in things like hail, low-level windshear and microbursts, while more frequent and powerful storms, both in summer and winter, will wreak logistical havoc at airports.



 

This subject is a tough one for me. It concerns me as a citizen, but it affects me on a personal level, too, and it leaves me feeling uneasy. I am, after all, an airline pilot.

I’m probably greener than most people, abiding best I can by the three Rs of good stewardship: reduce, reuse, recycle. I don’t own a car. I compost food scraps and recycle almost everything else. Much of the furniture in my apartment was scavenged from curbsides and refurbished by hand. I’ve replaced my incandescent light bulbs with compact fluorescents. But then I go to work and expel hundreds of tons of carbon into the atmosphere. Am I a hypocrite or what?

If I enjoy any consolation, it comes in knowing that commercial aviation’s share of greenhouse gasses remains, at least for now, pretty small. I’m the first to agree that airlines ought to be held accountable for their fair share of ecological impact, but that’s the thing: globally, commercial aviation accounts for only about two percent of all fossil fuel emissions. Commercial buildings, for one, emit a far higher percentage of climate-changing pollutants than commercial planes, yet there is little protest and few efforts to green them up. It’s similar with cars. Americans have staggeringly gluttonous driving habits, yet rarely are we made to feel guilty about them. U.S. airlines have increased fuel efficiency 70 percent over the past thirty years, 35 percent since 2001 alone, mostly through the retirement of fuel-thirsty aircraft. Average fuel efficiency of the American automobile, on the other hand, has stayed stagnant for at least three decades, and if the current political environment is any indication, it’ll be going backwards.

The sticking point, though, is that the true measure of aviation’s environmental impact goes beyond simple percentages. For one thing, aircraft exhaust—containing not only carbon dioxide, but also nitrogen oxides, soot, and sulfate particles—is injected directly into the upper troposphere, where its effects aren’t fully understood. As a rule of thumb, experts recommend multiplying that previously cited two percent fossil fuel figure by another 2.5 to get a more accurate total of the industry’s greenhouse contributions. Using this formula, airlines now account for about five percent of the problem.

That’s still not much, but civil aviation is growing rapidly around the world. China alone is planning to construct over forty large airports. In the United States, the number of annual passengers, already over a billion, is anticipated to double by 2030, at which point greenhouse gases from planes would rise to as much as five times current levels. If indeed we begin reducing the carbon output from other sources, as we keep promising to, the output from aviation will rise drastically as a percentage of the whole.

The reason for all of this growth is that hopping on a plane is relatively cheap and easy. That may change. Air travel will always be an economic necessity, but the kinds of flying we’ve become used to might not always be possible should petroleum prices climb.

Several carriers, meanwhile, are experimenting with biofuel alternatives to jet fuel. Air Canada, Qantas, United, and All Nippon Airways are among those that have operated revenue flights powered completely or partly by biofuel. In the meantime, many airlines allow passengers to purchase inexpensive carbon offsets when booking online. Or, for a small fee, there are third-party organizations that will offset the estimated CO2 of your journey, investing the money in sustainable energy projects.

Now forget emissions for a minute and let’s talk about other kinds of pollution:

One thing that always shocks me is the amount of material waste — namely plastics, paper, Styrofoam, and aluminum — thrown away by airlines and their customers. Take the number of trays, cups, soda cans, snack wrappers, and discarded reading material produced during the average flight, and multiply it by the tens of thousands of daily commercial departures around the world. Simple measures would go a long way toward reducing and reusing. For instance, why not offer passengers the option of receiving a cup with their beverage? My can of soft drink or juice always comes with a cup, dropped onto my tray before I have a chance to say no, even though it would be perfectly acceptable to drink from the container. And the packaging of airline food is nothing if not extravagantly wasteful. The typical inflight meal or snack consists of more petroleum-derived plastic than actual food.

Not all airlines ignore the waste problem. Virgin Atlantic’s onboard recycling program asks passengers to hand in glass bottles and cans and leave newspapers on their seats to enable recycling. At American Airlines, cans are recycled, with the money going to charity, and trash from domestic flights is separated and recycled after landing. Delta recycles all aluminum, plastic, and paper products from flights into its Atlanta megahub, with proceeds going to Habitat for Humanity. But while a few carriers are stepping forward, the industry-wide effort has, for the most part, been pretty halfhearted.



 

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