With the COP26 concluded a little over a week ago (November 13), here is something to ponder. Must we travel as much as we do on airplanes?
A flight from London to San Francisco releases approximately 5.5 tonnes of CO2 per person. By contrast, an entire year of driving a typical passenger car emits 4.6 metric tonnes. More than a whole year's car emissions released in one 11-hour flight.
Aviation is estimated to account for approximately 2.5% of global CO2 emissions. While this number may not sound significant, if aviation were a country, it would be sixth in the world. Forecasts estimate that by 2050, approximately 43 metric gigatons of carbon dioxide will be generated by aviation worldwide. And when the damage from aircraft includes the discharge of other gases and vapor trails in addition to the CO2, the total jumps to 5% of global emissions.
Contrails, the white streaks we see in the sky, are produced when hot exhaust gases come into contact with low-pressure, cold air. They contain black carbon particles. Moisture condenses on these to form ice. Though some contrails only last a few minutes, some join with cirrus clouds and other contrails, and this larger mixture can remain for up to eighteen hours. This contrail cloud mixture causes an effect known as 'radiative forcing'. The balance between heat emitted from the earth and that coming from the sun is altered. And this causes a change in climate. Thus, there is a double negative to aircraft - the CO2 emissions, and the radiative-forcing effect from the contrails.
It turns out the damage from contrails can be mitigated by changing flight paths. Researchers at Imperial College London have found that flight altitude changes of just 2,000 feet could curb the effect. A study of Japan's airspace found that changing just 1.7 percent of flights could cut contrail climate forcing by 59%.
Small changes in flight paths can significantly curb the impact of each flight, and at low cost. If these changes are implemented throughout the world, the effects could be significant.
Some airlines are leading the way towards environmental sustainability. Last winter, Air France KLM Martinair launched the world's first sustainable aviation fuels (SAF) program to reduce CO2 emissions.
Then there are innovators devising environmentally friendly small aircraft to one day meet some passengers' needs. As a start, the company Pipistrel received EU certification for its electric two-seater plane a little over a year ago. And Swiss flying school AlpinAirPlanes installed solar panels to recharge them (Engineering and Technology Magazine, Volume 16, Issue 7, August 2021).
For larger aircraft Rolls-Royce is in the process of developing hydrogen-fuelled engines that are likely to be available by 2035. They have three concept designs: a turboprop for 100 passengers, a turbofan for 200 passengers, and a futuristic blended-wing body design. Unfortunately there are many obstacles with hydrogen that lead some experts to believe that hydrogen aircraft are unlikely to be available until 2050 (Engineering and Technology Magazine, Volume 16, Issue 7, August 2021). Still, they do give us some hope for the future.
In the short term, Sustainable Aviation Fuel (SAF) has been introduced by Air France. It is a kerosene-like fuel but not derived from fossil sources. Such biofuels have difficulties of their own. It takes an enormous amount of crops to produce enough energy for aircraft, and the decision of the best use for those crops - food versus airlines -- is certainly not a clear-cut one. SAF is a very good idea but will be slow in transition, and during the next four decades when mitigating emissions is crucial, we must find alternatives.
Hydrogen or biofuels are the two likely choices for the future, and hydrogen as we know is a long process in development. In the meantime, while scientists work on improving flying options, what is the best way for us to reduce our carbon footprint, and still travel when we need to?
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