July 24, 2024

In the 2020s, there will be some big decisions to make about transport. It is the UK’s largest polluting industry. The UK government has responded haphazardly, opting to intervene and prevent the collapse of Flybe, Europe’s largest regional airline. He was then given the green light to build the high-speed rail system, HS2.

Decarbonising transportation would eliminate 26 % of UK CO2 emission, which comes from the way people travel. Boris Johnson, the Prime Minister, recently stated that this would raise “complex questions.” Johnson is right.

The Gilets Jaunes demonstrations against fuel tax increases in France illustrate how difficult it is to strike a balance between climate action, economic growth, and convenience. Why not invest in high-speed railways instead of letting a regional airline fail? The answer is not as simple.

Carbon footprints are misleading.

The aviation industry is the fastest-growing consumer of fossil fuels. Airlines contribute about 3.5% to all human-made greenhouse gas emissions. It may seem insignificant, but one transatlantic flight between London and New York can increase your carbon footprint as much as the heating budget for the average European.

Contrails, the white lines in the sky that we see when aircraft are flying high in the air, form in their wake. The ice crystals in these high-altitude clouds can trap heat, even though they are too thin for them to reflect sunlight. Contrails, unlike low-level clouds, which have a cooling effect, contribute to global warming. They increase the aviation industry’s greenhouse gas emissions by around 4,9%.

Flights contribute more to warming the atmosphere than their CO2 emissions. Aapsky/Shutterstock

Most people take the environmental benefits of high-speed railways for granted. The majority, but not all, of the research, suggests that it can offset aviation emissions if it is able to attract enough passengers. The relative climate impact of aviation compared to other modes depends on more than just the engines and altitude.

By calculating how much CO2 each form of transport produces when it moves one person one kilometer, we can compare their emissions. It reaches the amount of CO2 that leaves the exhaust of each vehicle but ignores the greenhouse gas emissions produced by the construction and maintenance of vehicles, infrastructure (such as airports, tracks, and runways), and fuel production.

Different greenhouse gases have other warming effects over different periods. These range from days of intense warming to decades of mild influence. To provide a standard unit of measurement for different gases, the warming effects are normalized over a certain period. The normal period is 100 years.

If it were five years, then the effect of the contrails would be more than the global warming caused by all the cars on the planet. They increase the temperature in the atmosphere with short bursts of intense heat. Over longer periods, such as 20 years, short-term effects become less significant, and aviation looks much better. Flying could be less harmful than driving a car over the same distance.

Most comparisons consider only the emissions from cars while they are in use. Khunkorn/Shutterstock

It’s not the end of the story. Energy inputs vary for different modes. Direct combustion of fossil fuels, such as jet kerosene, in aircraft engines emits greenhouse gasses. Electric high-speed trains emit no greenhouse gases unless fossil fuels power them.

Read more: Electric cars won’t save the planet without a clean energy overhaul – they could increase pollution.

Developing HS2 will mean deploying stations, tracks, and centers of communication, and they’ll need ongoing maintenance. These all need energy and material investments, which will create further greenhouse gas emissions through manufacture, transport, and use. That could increase the carbon footprint of rail by between 1.8 and 2.5 times, over just accounting for the operation of the trains. For aviation, the same infrastructure requirements are relatively small and are responsible for a 1.2–1.3 increase, with road transport showing a 1.4–1.6 increase.

Compare life cycles

The life cycle approach allows us to compare transport modes more fairly and understand where the emissions are coming from. The majority of greenhouse gas emissions from road and air travel are produced by driving and flying. In rail travel, however, the emissions generated in building the infrastructure dominate the climate impact. The heavy reliance of trains on electricity means that emissions are lower. There are also emissions associated with the production and maintenance of technologies for renewable energy.

All high-speed modes of travel have an environmental cost. Comparing the energy consumption and emissions of various transport options accurately is the first step in addressing the climate impact.

The government often tries to encourage people to change their behavior by reducing the number of flights that they take. In the case of HS2, however, the availability of regional flights will mean that only 4 % of drivers and only 1 % of airplane passengers may change their behavior.

Rail is often viewed as a carbon-free alternative to aviation. Governments must carefully weigh the climate impact of any transport project at every stage of its development.


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