Transport could burn up the EU’s entire carbon budget

The European Union (EU) is the world’s third-largest emitter of greenhouse gases and has a crucial part to play in achieving the 1.5ºC target of the Paris Climate Agreement. Since 1990, transport emissions in the EU have grown by 33% even as other sectors have reduced emissions by 32%. In 2018, domestic and international transport were responsible for 29% of total economy-wide greenhouse gas emissions in the EU. As shown in the figure below, light-duty vehicles (passenger cars and vans) are the greatest contributor to EU transport greenhouse gas emissions, followed by heavy-duty vehicles (trucks and buses), marine navigation, and aviation. This figure highlights direct transport emissions: emissions from fuel production, refining, and distribution are included in the other sectors total. Carbon dioxide accounts for roughly 99% of these direct transport carbon dioxide equivalent (CO2e) emissions, based on a 100-year global warming potential.

Figure 1. Share of EU-27 economy-wide greenhouse gas emissions in 2018 by transport subsector, including domestic and international components. Land use, land-use change, and forestry are included in the other sectors category.

Transport remains a key obstacle to achieving the EU’s climate targets, as shown in our recent analysis. Here we extend this analysis one step further to assess the compatibility of transport sector emission pathways with the Paris Agreement, which set a goal to limit global warming to well below 2ºC and preferably 1.5ºC above pre-industrial levels—we find that transport alone could emit more than the EU’s entire share of the 1.5°C carbon budget, even under an ambitious decarbonization policy scenario. Let us explain how we got there.

First, we draw on our recent analysis in which we modeled tailpipe CO2 emissions from road transport in the 27 countries that make up the EU (EU-27) under four policy scenarios. The most ambitious scenario we modeled, “higher ambition,” assumes a tightening of CO2 standards starting from 2025 that would improve internal combustion engine efficiency for all vehicle segments and achieve a transition to 100% zero-emission sales for light-duty vehicles by 2030 and for heavy-duty vehicles by 2040. This scenario would reduce tailpipe CO2 emissions to 94% below 1990 levels by 2050, versus only 24% below 1990 levels projected under currently adopted policies. Yet, even this “higher ambition” scenario would still result in 11.1 billion tonnes (Gt) of tailpipe CO2 emissions cumulatively from 2021–2050, which is more than 14 years’ worth of road transport tailpipe CO2 emissions at 2018 levels. This estimate also excludes fuel evaporative emissions and upstream emissions from fuel production, refining, and distribution.

Second, we develop simplified projections of tailpipe CO2 emissions from other transport subsectors: planes, ships, trains, and motorcycles. Assuming extensive mitigation actions (described in this Appendix), we project that these subsectors could add 7.5 Gt on top of road transport emissions, for a total of 18.6 Gt cumulatively from 2021 to 2050.

To put these cumulative emissions in context, let’s compare them to the remaining global carbon budget. The IPCC’s special report on 1.5°C states that, from the start of 2018, only 420 Gt CO2e –580 Gt CO2e can still be emitted for a 50%–67% chance of limiting warming to 1.5°C, not accounting for Earth system feedbacks that are expected to cause further warming. Taking the higher-probability budget and subtracting global emissions for 2018, 2019, and 2020 leaves a budget of 296 Gt CO2e from the start of 2021. Based on this budget, cumulative 2021–2050 road transport emissions in the EU-27 under our “higher ambition” scenario would burn 3.8% of the IPCC’s remaining global carbon budget for 1.5°C. Adding in our mitigation scenario emissions projections from other transport subsectors, we estimate cumulative 2021–2050 emissions from all EU transport would consume 6.3% of the global budget.

This raises an important question: how much of the global carbon budget can the EU burn? Many different methods have been used to apportion the global carbon budget to individual countries and regions. Here we present a range of outcomes based on three common methods: historical responsibility, population shares, and emissions shares. When emissions have been allocated according to historical responsibility, many sources have estimated that the EU’s share of the remaining global budget is near-zero or has already been exhausted. If future global emissions were instead allocated by current population shares, the EU would be allotted 5.8% of the remaining budget. Allocations based on current emission shares would leave 6.8% for the EU when land use, land-use change, and forestry emissions are included.

The figure below compares the remaining global carbon budgets for the EU derived from each of these allocation methods with our projections for cumulative 2021–2050 transport sector emissions in the EU. As shown here, even ambitious reductions across the EU transport sector would leave little room for emissions from all other sectors, which accounted for 71% of the EU’s GHG emissions footprint in 2018.

Figure 2. Projected cumulative 2021–2050 transport sector CO2 emissions in the EU-27 in the “higher ambition” scenario compared to the EU-27 fraction of the remaining global carbon budget allocated by historical responsibility criteria, current population shares, and current emission shares including land-use, land-use change, and forestry.

The EU’s post-2021 light-duty vehicle CO2 standards will be reviewed by the European Commission this year, and a review of heavy-duty standards is planned for 2022. That road transport in the EU accounts for such a sizable fraction of global emissions underscores the role of the EU’s vehicle CO2 standards in limiting global warming to 1.5ºC. Yet, even under the most ambitious scenario for these CO2 standards that we modeled, EU road transport alone would still emit nearly 4% of the remaining global carbon budget associated with a 67% chance of limiting warming to 1.5ºC, and the EU transport sector as a whole could emit more than the entire EU economy’s share of the budget. These sobering findings show that the EU’s transport sector must decarbonize much faster than envisioned by current sectoral policies and targets, including those for road transport, aviation, and marine navigation. A good place to start is with the upcoming reviews of the EU’s post-2021 CO2 standards for new light- and heavy-duty vehicles. As for their stringency? If EU regulators are serious about limiting warming to 1.5ºC, they should strengthen these CO2 standards to the highest ambition feasible and pair them with complementary policies.