Maritime shipping and commercial aviation contribute significantly to the global economy, making up about 16% and 4% of global GDP, respectively. Ships move 80-90% of the world's goods, and aviation transported 4.5 billion passengers annually at its peak before COVID-19 in 2019. However, both modes contribute a growing share of carbon dioxide (CO2) emissions.

Without urgent action, aviation and shipping will contribute a growing proportion of GHGs.

Aviation is currently responsible for about 3% of global energy-related CO2 emissions (about 1 gigaton, roughly equal to the annual emissions of Japan). This share is projected to rise to 4.5% by 2050 (2 gigatons) as the demand for air travel recovers from its COVID-19 slump and continues to increase. In addition to CO2 emissions, aviation also contributes to climate change via the warming effects of water vapor in contrails.

The use of passenger aviation is incredibly concentrated, too — in 2018, only 2 to 4% of the global population flew internationally. High-income countries are responsible for the largest share of aviation emissions. The United States alone contributes about 23%, and the next largest emitter is China at just over 10%.

In 2019, short-, medium-, and long-haul flights all emitted equal shares of CO2 emissions. Where possible, it is ideal to replace short-haul flights with bus or rail trips.

Maritime shipping accounts for almost 3% of global greenhouse gas (GHG) emissions. Roughly 85% of these emissions come from international shipping — the transport of goods by container ships, bulk carrier ships, and tankers.

Although shipping has become more energy-efficient since 2012, emissions from the sector could increase by up to 30% above 2008 emissions by 2050, due to increased demand for international goods. Notably, if we succeed in reducing the demand for fossil fuels, the decreased trade in fossil fuels may cut this demand growth.

Several new options for zero-emission aviation and shipping are emerging, but they need to be deployed at scale as soon as possible.

Shipping and aviation in a 1.5 degrees C (2.7 degrees F) world will constitute an efficient, well-run movement of people and goods with minimal CO2 emissions. To accomplish this, the world must decrease travel via planes using fossil fuel and ships using heavy fuel oil.

This includes reducing demand for travel, making operational and efficiency changes, and shifting air and sea travel to vessels using zero-emission options. Electricity, green hydrogen, ammonia, and, in some limited cases, advanced biofuels all hold potential. But because these solutions are either nascent or have not yet had commercial breakthroughs, additional public and private research and investment will be necessary to meet our climate goals.

Data Insights

Is the world making enough progress toward the most important outcomes?

Systems Change Lab assesses progress made toward targets across 2 outcome indicators. Click a chart to explore the data.

What factors may enable or prevent change?

Systems Change Lab identifies 12 enablers and barriers that may help spur or impede change. Click a chart to explore the data.

Progress toward targets

Systems Change Lab tracks progress made across 2 outcome indicators. outcome indicator. Explore the data and learn about key actions supporting systems change.

Share of zero-emission fuels in marine shipping fuel supply

Scenarios aligned with a 1.5 degrees C pathway suggest that 93% of fuel used in maritime shipping will need to be zero-emission by 2050.

Transitioning the global maritime sector will require new zero-emission fuels (ZEFs) and additional investments beyond the fuels themselves, including new technologies to retrofit vessels to run on ZEFs.

ZEFs include green ammonia, green hydrogen, e-methanol, and synthetic e-fuels produced from renewable sources of energy. E-methanol and synthetic fuels made with renewable electricity still release some carbon dioxide (CO2)  when combusted, so, to produce net-zero emissions, some CO2 used to synthesize these fuels will also need to be captured from the atmosphere. While batteries are also a zero-emission option, their relatively low energy density makes them unsuitable for long distance shipping but can contribute to decarbonizing shorter domestic voyages.

As of 2021, the global share of ZEFs in shipping remained close to 0%. The uptake of green ammonia and green hydrogen, and construction of zero-emission ships capable of running on such fuels, remained in their infancy. 

Currently, ammonia engines are expected to be commercially ready by 2025, while hydrogen engines already exist and other demonstration projects are underway, with a noticeable uptick of the latter appearing on today’s order books for new ships. 

To keep the world in line with a 1.5 degrees C (2.7 degrees F) scenario, the share of these fuels should reach 5% by 2030.

Share of sustainable aviation fuels in global aviation fuel supply

The share of sustainable aviation fuels remained at negligible levels in 2022. Considerable effort will be required to reach 13% in 2030, but there are signs that supply and use is beginning to grow, albeit slowly for now.

Decarbonizing aviation will be heavily dependent upon a transition to sustainable aviation fuels (SAFs), which include power-to-liquid synthetic fuels and biofuels. In addition to cutting greenhouse gas (GHG) emissions, switching to SAFs can also enable a reduction of air pollutants such as sulfur emissions and particulate matter. Alternatives to drop-in fuels, such as powering planes with batteries or hydrogen, may also play some part in decarbonizing aviation. 

The share of SAFs in the aviation industry remained low in 2022, accounting for 0.1% of the total aviation fuel consumption. While there are no guarantees, the rate of change will likely be nonlinear in the future. Global progress made toward this near-term target is well off track. The technology is nascent and remains in the emergence stage of an S-curve, so the share would have to double every year in order to meet the 2030 target.

Enablers and barriers

We also monitor change by tracking a critical set of 12 enablers and barriers enabler or barrier that can help spur or impede change. Explore the data and learn about key actions supporting systems change.

Number of companies investing in zero-emission fuel storage infrastructure

As of the end of 2021, 32 signatories to the Call to Action for Shipping Decarbonization were developing bunkering infrastructure for zero-emission fuels.

Using zero-carbon fuels for marine shipping will require new shoreside infrastructure to deliver the fuels to the ships. This is referred to as bunkering infrastructure. Many ports around the world have invested in new bunkering infrastructure in recent years, but this has typically been for liquefied natural gas (LNG).

Bunker infrastructure for LNG was available at 141 ports at the end of 2021. However, the role of LNG in decarbonizing shipping is in question because of concerns about methane leakage (both upstream and in use on vessels), increasing emissions, and because a lot of energy is needed in the liquefaction process. Also, although LNG releases less carbon dioxide (CO2) at combustion than heavy fuel oil, it is not a zero-carbon fuel and its emissions would need to be accounted for. Because existing bunker infrastructure for LNG can only be converted to contain a few types of zero-emission fuels, most new construction will require a different kind of infrastructure.

In 2021, 237 companies across the maritime shipping value chain signed on to the Call to Action for Shipping Decarbonization, which called on world leaders to commit to decarbonizing shipping and provide funding and policy support along the way. As of the end of 2021, 32 signatories to the Call to Action were developing bunkering infrastructure for zero-emission fuels. Most of the entities developing bunkering infrastructure are ports, and this work is occurring on every inhabited continent. This indicator is a proxy for the broader investments in bunkering infrastructure, for which there is no publicly available data.

Number of companies committed to procuring zero-emission ships

As of the end of 2021, 63 companies had signed deals to procure zero-emission ships, which are expected to be commercialized in the 2030s.

Using zero-emission fuels in combustion engine ships will help lower emissions. So will developing new ship designs that allow for the use of 100% zero-emission fuels, electricity with batteries, green hydrogen, or other zero-emission solutions.

The most straightforward way to understand the state of demand for zero-emission ships is to measure the number of companies committed to procuring these vessels for use in their shipping activities. In 2021, 237 companies across the maritime shipping value chain signed onto the Call to Action for Shipping Decarbonization, which called on world leaders to commit to decarbonizing shipping and provide funding and policy support along the way. As of the end of 2021, 63 of those 237 companies had signed deals to procure zero-emission ships.

Because the zero-emission fuels that these ships will use are nascent, demand is low, but it is reasonable to expect that it will increase as more options emerge. Zero-emission ships are currently in the concept stage and are expected to be commercialized in the 2030s. It is likely that these commitments will provide certainty to manufacturers that demand exists, and as more options emerge and shipping companies understand that the technology is ready, it is reasonable to expect that commitments will increase. The number of signatories to the Call to Action is a proxy for the broader private sector commitment to procure zero-emission ships, for which there is no comprehensive, publicly available data.

Number of countries with policies supporting the development of advanced biofuels

Advanced biofuels are still in their development phase and will require vastly greater levels of investment to help decarbonize hard-to-abate sectors like aviation and shipping. Only nine countries were identified as having policies supporting advanced biofuel development as of 2020.

Advanced biofuels are those produced from non-food or non-feed inputs such as algae or waste organic matter. They provide a more sustainable alternative to conventional biofuels that compete with food production, drive global food prices higher, and take up arable land that contributes to otherwise deforestation. Conventional biofuel production is also water-intensive, with every liter of ethanol requiring up to 63 liters of water to produce.

Advanced biofuels are still in their development phase and will require vastly greater levels of investment to help decarbonize hard-to-abate sectors like aviation and shipping. They could also play a key role in decarbonizing the large number of fossil fuel cars that will remain on our roads into the future.

Only nine countries were identified as having policies supporting advanced biofuel development as of 2020; all but two — the United States and India — are in Europe.

Global research and development spending on zero-emission shipping

Because zero-emission solutions for shipping, including fuels and ship design, are not commercially viable yet, more work must be done to develop, prove and scale them.

Because zero-emission solutions for shipping, including fuels and ship design, are not yet commercially viable, more work must be done to develop, prove, and scale them.

Measuring spending on research and development (R&D) helps us understand how much effort is being put into developing new solutions in a particular industry, and there is a positive relationship between R&D spending and the number of patents for new technologies.

There is currently no publicly available information on global spending on R&D for zero-emission shipping fuels and ship design.

Number of major freight demanding companies committing to use zero-carbon shipping fuels by 2040

As of 2023, 19 companies have committed to, among other things, leveraging their freight demand to support only shipping services powered by zero-emission fuels by 2040.

A key step in developing zero-emission fuels is proving that demand for the fuel exists: it unlocks financing, draws more players to the field, and, ultimately, ensures that the fuel makes it into real-world use.

The most straightforward way to understand the state of demand for zero-emission shipping fuels is to measure the number of companies committed to running vessels on these fuels. In 2021, the Aspen Institute brought together nine major companies with large shipping demands, including Amazon, Ikea and Unilever. These nine companies committed to, among other things, leveraging their freight demand to support only shipping services powered by zero-emission fuels by 2040. Encouragingly, an additional 10 companies made similar commitments in 2022, taking the total to 19 companies as of 2023.

Because zero-emission shipping fuels are nascent, demand is low, but it is reasonable to expect that it will increase as more options emerge. The number of companies in this coalition is a proxy for the broader private sector commitment to source zero-emission shipping fuels, for which there is no publicly available data.

Number of governments in Mission Innovation's Zero-Emission Shipping Mission

Mission Innovation, an effort by major global economies to increase research and development spending on critical advancements in clean energy, established the Zero-Emission Shipping Mission in 2021. As of 2023, 14 governments are participating.

Although governments typically are not involved in the production of ships, they set the policies and regulations that govern maritime shipping. Governments can set policies, establish strategic pathways, and put in place requirements that provide signposts and regulatory certainty for the companies that supply and procure ships.

Mission Innovation, an effort by major global economies to increase research and development (R&D) spending on critical advancements in clean energy, established the Zero-Emission Shipping Mission in 2021. As of 2023, there are 14 governments participating in this effort: Australia, Canada, Denmark, the European Commission, France, Germany, Ghana, India, Morocco, Norway, Singapore, South Korea, the United Kingdom, and the United States. These governments have pledged to work with the private sector to develop zero-emission ships, fuels and fueling infrastructure.

This indicator is a proxy for broader government commitment to zero-emission shipping decarbonization, for which there is no publicly available data.

Global research and development spending on zero-emission aviation

Measuring spending on research and development (R&D) helps us understand how much effort is being put into developing new solutions in a particular industry, and there is a positive relationship between R&D spending and the number of patents for new technologies.

Because zero-emission solutions for aviation fuels and plane design are still nascent, more work must be done to develop, prove and scale them. Most attention is focused on liquid fuels and hydrogen, although recent advancements may allow for new options in electric aviation in the coming decades.

Measuring spending on research and development (R&D) helps us understand how much effort is being put into developing new solutions in a particular industry, and there is a positive relationship between R&D spending and the number of patents for new technologies. There is currently no publicly available information on global spending on R&D for zero-emission aviation fuels and plane design.

Number of companies committing to accelerate sustainable aviation fuel

The most straightforward way to understand the state of demand for sustainable aviation fuels is to measure the number of companies committed to procuring these fuels for their planes. As of 2020, 71 companies were members of the Clean Skies for Tomorrow coalition.

A key step in developing sustainable aviation fuels (SAFs) is proving to producers that demand for the fuel exists: it unlocks financing, draws more players to the field, and, ultimately, ensures that the fuel makes it into real-world use. The supply of aviation fuels typically comes from petroleum producers and refiners, and the SAFs that exist currently come from specialized producers and refiners as well. Demand for fuels typically comes from airlines and airports, but logistics companies also participate.

The most straightforward way to understand the state of demand for SAFs is to measure the number of companies committed to procuring these fuels for their planes. As of 2020, 71 companies were members of the Clean Skies for Tomorrow coalition. These companies include producers such as Shell and SkyNRG, airplane manufacturers such as Boeing, airport owners such as Dubai Airports and Corporación América Airports, airlines such as Lufthansa and Southwest, government agencies such as the Indian Renewable Energy Development Agency, and funders such as BlackRock and the Indian National Bank for Agriculture and Rural Development.

Because SAFs are nascent, demand is low, but it is reasonable to expect that it will increase as more options emerge. This indicator is a proxy for the broader private sector commitment to decarbonize aviation, for which there is no publicly available data.

Investments in research and development for aviation

Corporate investments in research and development for aviation have grown slightly, from $12.7 billion in 2015 to $13.7 billion in 2022. More investment will be needed to bring new solutions such as sustainable aviation fuels and battery electric planes to scale.

Developing new solutions for aviation, such as sustainable aviation fuels (SAFs, including sustainable biofuels and synfuels made from green hydrogen and captured CO2) and battery electric planes, requires significant research and development (R&D) spending.

From 2015 to 2022, publicly listed companies increased their investments in aviation R&D from $12.7 billion to $13.7 billion per year. These investments included new SAF production, such as a $2.2 billion expansion of Neste’s waste-to-fuel refinery in Rotterdam, which will bring the company’s SAF development capacity to 1.2 million tons per year. However, SAFs are not the only solution requiring R&D, so the $13.7 billion likely also includes new energy efficiency measures, new engines and new plane designs. A breakdown by technology is not available, so these investments may also be going to innovations that are not sustainable.

New funding opportunities, such as the $9.4 billion offered by the Inflation Reduction Act for SAF development in the United States, and new requirements like the European Union’s 70% SAF requirement by 2050, are likely to help drive additional corporate R&D spending in the coming years. However, it will be key to ensure that SAFs are developed sustainably and with as few emissions as possible.

The Inflation Reduction Act, for example, provides a credit for fuels that reduce emissions by at least 50% compared to fossil jet fuel (with greater incentives to go beyond 50%), but reductions at or close to 100% would be necessary for net-zero emissions by 2050. Fuels such as those made by combining green hydrogen with carbon dioxide captured from the atmosphere or alternative propulsion with batteries could help deliver these much steeper emissions reductions.

Investments in research and development for shipping

Investments in research and development for shipping have fluctuated slightly but remained around $3 billion per year from 2015 to 2022. More investment will be needed to bring new solutions like zero-emission shipping fuels to market and scale.

Developing new solutions for shipping, such as zero-emission shipping fuels, requires significant research and development (R&D) spending. Investments in R&D for shipping have fluctuated slightly but remained around $3 billion per year from 2015 to 2022. Companies are working to develop zero-emission fuels, but these investments likely also include new energy efficiency measures, new engines, and new ship designs.

R&D investments to tackle greenhouse gas (GHG) emissions may see a significant increase soon, however, as the International Maritime Organization approved a new policy in 2023 requiring net-zero emissions “by or around” 2050 and specifically requiring zero or near-zero fuels to make up 5–10% of shipping energy consumption by 2030. Given that currently operating ships do not use any zero-emission fuels, meeting these goals will require a significant uptick in R&D and market development to bring zero-emission fuels to scale.

Cost of sustainable aviation fuels

As of 2020, producing e-kerosene for aviation was estimated to cost seven times fossil jet fuel. Transitioning to sustainable aviation fuels necessitates that the costs of these fuels come down dramatically in the near-term.

Sustainable aviation fuels (SAFs) will be vital to decarbonize the aviation sector. Alongside the electrification of aircrafts, SAFs such as green hydrogen, sustainable biofuels and synfuels could play an important role in zero-carbon fuel supplies for aviation. For the moment, only a negligible quantity of SAFs have been adopted by the aviation sector, mainly due to a lack of global supply and their associated costs.

To stay on track for a 1.5 degrees C (2.7 degrees F) scenario, the share of SAF needs to reach 13% in 2030 and 100% in 2050. However, SAFs that emit zero or net-zero CO2 are nascent, and therefore they cost much more to produce than their fossil fuel equivalents. For example, e-kerosene for aviation was estimated in 2020 to cost $8.80 per gallon to produce in the United States, whereas fossil kerosene cost $1.30 per gallon to produce. Additional policy support, including the kinds of mandates for use that are emerging in the European Union alongside other efforts such as carbon pricing, will be necessary to bring these fuels to scale and therefore drive down their costs.

Cost of zero-emission shipping fuels

As of 2020, producing green ammonia for shipping was estimated to cost up to three times that of fuel oil. Transitioning to zero-carbon fuels in the maritime sector necessitates that the costs of zero-emission fuels come down dramatically in the near-term.

The maritime sector currently emits around 3% of global emissions. Zero-emissions fuels (ZEFs) will be vital to decarbonize the shipping sector. Although there is some uncertainty around which fuels could dominate the zero-carbon fuel market for shipping, green hydrogen, synthetic fuels, and green ammonia are currently the leading contenders. For the moment, zero-emission fuels have not yet entered the maritime shipping fuel supply, mainly due to a lack of global production and their associated costs. In the European Union, for example, green ammonia for shipping was estimated in 2020 to cost €500-1,300 ($550-$1,400) per ton to produce, whereas very low-sulfur heavy fuel oil cost €480-540 ($520-590) per ton.

Scenarios aligned with a 1.5 degrees C (2.7 degrees F) pathway suggest that 5% of fuel used in maritime shipping will need to be zero-emission by 2030 and 93% of fuel by 2050. Additional policy support, including the kinds of mandates for use that are emerging at the International Maritime Organization alongside other efforts such as carbon pricing, will be necessary to bring these fuels to scale and therefore drive down their costs.