Carbon pricing makes fossil fuels more expensive, encouraging more efficient aircraft operations and incentivising the use of sustainable alternative fuels with lower emissions. A successful ETS requires the price of carbon to be high enough. If the resulting increase in airlines’ operating costs are passed on to passengers, passenger demand growth for aviation would likely decline.

The World Bank reported that the average price per tonne of carbon in the EU ETS was EUR 25 (nominal figure from 1 April 2019). The ITF’s (2019) Transport Outlook assumed a carbon price of USD 100 per tonne of CO2 by 2050 based on current commitments, as part of a range of assumptions. Under this scenario, emissions from international passenger aviation are projected to grow by 82%. Under more ambitious scenario assumptions, which include electric aircraft being operational for short-haul flights, a price of USD 500 per tonne is assumed. This package of measures sees a 19% fall in international aviation emissions.

The EU predicted that emissions from sectors covered by the EU ETS will be reduced by 43% between 2005 and 2030.

The CO2 reduction benefits of fuel or carbon taxes come mainly from demand reduction, provided the level of tax is high enough to induce a demand shift.

Fuel taxes also incentivise increased aircraft efficiency, which further reduces CO2 emissions per aircraft.

Carbon taxes on the other hand directly target CO2 emissions. Fuel or carbon taxes would likely push the sector towards less carbon-intensive or carbon-free fuel alternatives. This can potentially lead to a significant CO2 reduction in the long term.

A European study found that a tax of EUR 330 per 1000 litres of kerosene could result in an average reduction in CO2 emissions of 11%, based on the resulting increase in ticket price and reduction in demand. National reductions were estimated to range between 4% and 19%.

Another study found a globally applied fuel tax would reduce emissions by 3.3% for a tax of USD 63 per 1000 litres to 13.1% for a tax of USD 293 per 1000 litres.

An estimate suggests a globally applied carbon tax of USD 200 per tonne of CO2 could reduce aviation emissions by 8% comparing 2024 to 2004 levels.

The ITF estimates that a cumulated 630 MtCO2 will need to be offset by 2030 for international aviation to achieve carbon-neutral growth from 2020, with 115MtCO2 being offset in 2030. 70 MtCO2 per year on average would be offset between 2021 and 2030. This represents 13% of international aviation emissions in 2019 (527 MtCO2). Although domestic aviation emissions accounted for 320 MtCO2 in 2019 -  37% of total aviation emissions - the CORSIA covers international aviation only.

However, carbon offsetting does not lead to actual direct emissions reductions within the international air transport sector. If offset prices remain low, they could fail to incentivise in-sector emissions reductions and investment in cleaner technology.

It is unclear to what extent ICAO will be able to enforce CORSIA. The scheme is being implemented through Standards and Recommended Practices (SARPs), which have to be implemented in national law to become binding.

The CO2 reduction of MaaS are achieved through sustainable travel and reducing the demand for private car travel. The sub-modes that MaaS comprises are the source of CO2 reductions, compared to conventional private cars.

MaaS can lead to CO2 reductions by responding to passengers' needs for services like on-demand shared buses and efficient payment systems which can stimulate shift from private car to public transport. Although the studies available are mostly small-scale, the findings indicate reduced private car use. The study for Ulm (Germany) shows that in the most plausible scenario the CO2 emissions per average car2go user would reduce from 2787 to 2549 kg CO2/year due to the modal shifts. This result comes from a model rather than from empirical evidence.

CO2 reductions from car sharing systems stem from:

• Reductions in car sharers' total vehicle kilometres (thanks to an increased use of public transport or active modes encouraged by the scheme), and/or
• The replacement of private vehicle trips with shared vehicle trips (depending on the fuel-efficiency of the respective vehicles).

These effects will increase in cases where individuals decide to entirely abandon their private vehicles in favour of car sharing. Research suggests that around 13-17% of car sharers sell a private car. Effects will increase where ultra-low-emission vehicles are used in sharing schemes.

The available literature suggests that car sharers reduce their transport-related CO2 emissions by between 30% and 70%, with most estimates converging around 40-45%.

In Europe, the available evidence is not conclusive enough to observe any savings. Similarly, in South Korea, if the vehicles were not replaced by electric vehicles, no savings could be obtained.

CO2 reductions from car restriction policies come from reduced car traffic and congestion during the time when the restriction is in place. Depending on the design of the scheme, a decrease of private vehicle travel of about 5-10% can be expected.

Usually peak hour car restriction schemes have fewer side effects regarding increased car ownership levels, where users can choose between different cars during times of access restrictions. However, their effects are typically smaller since commuting patterns may shift to different times, rather than to cleaner modes, to avoid the times of restrictions.

In general, CO2 benefits are not seen to be substantial, especially if restriction schemes are not introduced in combination with other measures.

CO2 benefits of access restriction zones may originate from mode shift, for example to public transport or more fuel efficient vehicles. If the criteria for access restrictions concern a large share of the available vehicle stock in a city or its surroundings, congestion can also decrease, especially in the first years after the introduction of the access restriction zone.

Literature and related case studies that assess the impact of access restriction zones for passenger vehicles on CO2 emissions could not be identified. Assessments typically focus on the impact of such zones on air pollutant emissions.

Reducing speed limits from 50km/h to 30km/h can reduce fuel consumption - and related emissions - by 7%, if rapid acceleration and deceleration are avoided. A 10 km/h speed reduction from 60 km/h to 50 km/h can achieve a 5% reduction in CO2 emissions. There is much debate as to whether and to what degree speed limitations achieve CO2 and other pollutant emissions reductions, however. The most fuel-efficient driving is at around 50 to 60km/h.

Integrated ticketing systems (ITS) typically increase the modal share of public transport in the short and long term.

The introduction of ITS on a set of European cities accompanied an increase in public transport (PT) demand of between 4% over two years in Manchester (UK), to 33% over 18 years in Paris (France). It remains difficult to isolate the sole impact of integrated ticketing on the increased public transport demand, however.

Increases of between 1% and 3% in public transport use can occur from implementing advanced traveller information systems.