Train, car, plane: what to take into account when calculating the carbon footprint?

The situation may seem incongruous: in the Alpine valleys, elected environmentalists have long opposed the construction of a train line. The Lyon-Turin rail tunnel is dedicated to connecting Auvergne-Rhône-Alpes with the Italian Piedmont and it is sparking debate: its construction is fifteen years late and its costs have exploded by 85% according to the European Court of Auditors. Its promoter, Tunnel Euralpin Lyon Turin (TELT), still defends that the work will make it possible to transfer goods from roads to railways, thus decarbonizing the flow of cross-border goods. However, the site’s CO2 footprint leaves something to be desired.

TELT estimated in 2012 that the construction of the cross-border link would generate 10 million tons of CO equivalent2 (teqCO2). Based on the contracting authority’s traffic assessments, the European Court of Auditors concluded that the emissions from Lyon-Torino would not be offset until twenty-five years after its commissioning. Provided that the presented projections were not exaggerated, the institution qualifies: “This prediction further depends on traffic volumes: if they only reach half the predicted level, it will take fifty years from the commissioning of the infrastructure before CO2 emitted by its construction is compensated.”

An example and a doubt sometimes used by aviation defenders to increase the trains’ carbon footprint. With reason?

Consider emissions to produce energy

First we need to remember the orders of magnitude. According to the latest report from the Intergovernmental Panel on Climate Change (IPCC), 15% of global CO2 emissions2 produced directly by the transport sector. Even more if we include indirect emissions: energy production and infrastructure construction. Because the artificialization of soil and the destruction of wetlands prevent the capture of CO2 at these coal drains. Still according to the IPCC technical overview, 70% of emissions come from road transport, 12% from aviation, 11% from sea transport and 1% from rail transport.

The first factor to be taken into account when estimating emissions: the use and origin of the energies from the different types of transport. “That is, the combustion as well as the emissions associated with the upstream energies, explains Nicolas Meunier, mobility expert at Carbone 4. For transport powered by electricity, it is e.g. manufacturing emissions from nuclear and renewable energy parks. In the same way in diesel, you have to take into account the extraction, refining and transportation of oil.”

It is on these criteria that the CO2 emission calculator from the French Environment and Energy Management Agency (Ademe) is based, which calculates the CO2 footprint of any trip. , but does not take into account the construction of vehicles or infrastructure.

To calculate the CO2 footprint for the various transports, “taking into account the plant emissions from airports and railways is useless when you think in the short term for your next trip”, disc Nicolas Meunier. Emissions from the construction of rail infrastructure have already been emitted and are ultimately amortized by moving passengers to this low-carbon transport, where airport and road infrastructure will continue to serve vehicles whose technologies currently do not allow to reduce its impact.

Effects on the climate excluding CO2

For a similar trip, “the airplane is 40 to 130 times more emitting than the train, [selon] whether we integrate Intercités, some of which have heat engines, compares Valentin Desfontaines, responsible for sustainable mobility in the Climate Action Network (RAC) by basing his calculation on Ademe’s carbon base. A TGV journey costs 1.73 grams of CO2 kilometers per passenger (gCO2e/, against 230 grams of CO2 for a domestic flight.

Aviation’s impact is increased by its units’ contrails. “It is a matter of taking into account all effects excluding CO2, says Nicolas Meunier, the aircraft will burn off kerosene at very high altitudes, where the water vapors produced by combustion can form clouds, this is called condensation draft. These clouds have a warming effect on the climate.”

Differences between construction and energy/maintenance emission factors for different modes of transport. | Carbon cabinet

And even by incorporating the construction of vehicles and infrastructure in the calculation of carbon emissions, the results obtained by the company Carbone 4 underline the sobriety of the train compared to other forms of transport. For a similar journey, a TGV would emit 10 gCO22e/, a 30 gCO coach2e/, an electric car 51 gCO2e/, a 109 gCO thermomobile2e/, and a 264 gCO aircraft2e/

A “common” train line written off in twelve years

On the site Lyon-Torino, a monumental project across the Alps, Valentin Desfontaines prefers to take the construction of the LGV Rhin-Rhône line as an example, which is more common. Open to traffic since 2011, this high-speed line connects Grand-Est and Bourgogne-Franche-Comté.

Its carbon footprint, which Ademe, SNCF and RFF (Réseau ferré de France) have entrusted to the firms Objectif Carbone, Altern Consult and Inexia, reveals the carbon bill for the first thirty years of operation. Design, construction and operation must generate 1.9 million teqCO22of which 42% is due to works and 53% to the production of energy for traction.

“On average, 1.2 million people should be diverted annually from road and air thanks to the new TGV Rhin-Rhône offer”shows the study for a period between 2012 and 2042. This is a saving of 3,895,000 teqCO2 over thirty years.

The line would become “carbon positive” in 2024, i.e. the avoided emissions will be greater than the emissions generated by its design, operation and maintenance. A result that is all the more beneficial since, as the study points out, “the operation and environmental benefits of the line will continue well beyond the thirty years taken into account, and the lifespan of an infrastructure is around one hundred years”.

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