When it comes to global carbon emissions, transport–particularly long-distance transport–is one of the main culprits. Although countries across the globe are banding together to reach net zero goals, the transport sector is responsible for 21% of global carbon emissions. That number is expected to continue to grow by 20% by 2050. What is it about transport that makes it so challenging to decarbonise? And what are the possible solutions and innovations that help reduce emissions in this sector? Let’s take a look at the main challenges facing long-distance transportation from a sustainability standpoint.
Before we consider the technological challenges around transport decarbonisation, we need to look at a more demographic issue. One of the main challenges for transport–whether that’s travel or goods–is the increase in demand. With population and economic growth, there will be an increase in demand for goods and leisure travel. If we don’t consider the growth in the market, even highly ambitious policies could only reduce emissions from transport by 70%, a nice number, but it’s not zero. Couple that with the likelihood that transportation as a sector will grow, and you’ll be able to see that even a 70% reduction in emissions won’t be enough.
On a global level, transportation is expected to more than double in number by 2050 when compared to 2015. Even if emissions are reduced by 70%, without reducing the demand for transport, decarbonising will only offset the projected growth in emissions. Without reducing the demand for transportation, it’ll become impossible to meet the decarbonisation targets set by the Paris agreement by 2050. This is not a technological issue but a demographic and logistics one. Transportation will need to consider how often and far people and goods will travel.
Many place their hopes in electric vehicles (EVs) as paving the way for the future of decarbonised transportation, but even this is not an ideal solution. At present, we rely too much on fossil fuels like oil, with petroleum fuels making up 91% of U.S. and 95% of the EU transportation in 2019 and 2018, respectively. Moving transportation away from oil is more challenging than it may seem. Let’s discuss more why this is the case.
Fuel needs to be energy dense–and contain a lot of energy for its weight and volume. Petroleum-based fuels, particularly liquid fuels, are ideal for transportation as they are easy to move, store, and pump into the tank while also meeting the energy needs of transportation. Then there is the technological barrier, as most internal combustion engines in vehicles have been built with liquid fuels in mind.
EV sales have reached a record high, despite barriers like the pandemic and supply chain issues affecting components like semiconductor chip shortages. In 2021, EV sales doubled to 6.6 million, compared to 2020. EVs could be the key to decarbonising road transport, which accounts for 16% of global emissions.
This is excellent news, but the deployment of charging infrastructure for EVs at the current demand has yet to arrive. What this means is that EV owners are limited to shorter trips, as long road trips are just not feasible as there are not enough options available for charging electric cars, especially if the EV owner is driving through areas lacking in electrical grid infrastructure and additional power that can support EV charging.
Also, some modes of transport are easier to decarbonise than others. EVs could be a solution to cut road transport emissions, but there needs to be sufficient charging capacity available for longer journeys. So, while replacing oil will be easier in small vehicles that carry lighter loads and have frequent opportunities for refuelling, EVs are not the be-all-end-all solution, particularly for medium to large vehicles.
Heavy trucking, shipping, and aviation, whether moving people or goods over long distances, rely on energy-dense fuel, and electric batteries cannot cope with this demand. This means that for this sector, we need to look elsewhere for a solution to find an alternative fuel source that can provide the energy density you’d get with petroleum fuels. Biofuels or fuels like hydrogen or synthetic fuels could help decarbonise long-distance, heavy transportation. However, these fuels also come with their own challenges, aviation and shipping being the most complicated, so let’s look at road transportation for now.
Since 2000, road transportation of freight has been the fastest sector of oil growth demand and makes up 20% of the global oil demand. However, while freight corridors can be used to help transportation become more efficient and reduce emissions, medium and heavy-duty road vehicles require innovation. EVs could provide a solution for those that operate in limited areas and have set routes with regular charging stations, like buses used for public transportation in a city. Urban delivery vehicles and service vehicles could also be electrified.
For long-haul transportation, EVs have the challenge of range and payload, not to mention that batteries are also heavier than liquid fuel, so electric trucks, especially those that transport heavy goods, would need frequent charging. Some initiatives, like those proposed by the California Air Resources Board (CARB), want to set up regular charging stations along freight routes to allow long-distance transportation to apply EV technology.
However, another alternative here is looking into fuels like hydrogen, which has the advantage of the overall energy system like conventional fuels. Still, the technology needs to be developed more when compared to EVs. A compromise that may work to decarbonise medium to heavy-duty road transport is to use hydrogen as a backup for EVs, with vehicles that both can power–using electricity when charging is available and hydrogen when there is no ability to charge.
Aviation and shipping have a few characteristics in common regarding the sustainability question. They both involve large and heavy vehicles that travel long distances, where frequent refuelling or charging is impossible. Also, their emissions occur in international airspace or waters beyond the boundaries of a single country.
When flying a plane, the fuel must be enough to get the plane off the ground to cruising altitude. Airlines are reluctant to get too experimental as it could put many lives at risk should something go wrong or the fuel is insufficient. For obvious reasons, electric batteries are not an option for planes, so we’d need to look towards an alternative like biofuels. Small quantities of biofuels are already used in aviation, which are derived from waste fats and vegetable oils blended with petroleum-based jet fuel. However, an increase in demand for biofuels could have other impacts. For example, if biofuels come from food production, this could increase food prices and competition for arable land.
Hydrogen is another option, as it has the high energy density needed to meet fuel demands, and while hydrogen weighs less, it takes up more space, so larger fuel tanks would be required, so you’d need bigger planes. Also, aviation and hydrogen already have a murky history together–the Hindenburg springs to mind–so there is some understandable reluctance and safety concerns as the fuel is flammable at lower temperatures. However, hydrogen could still be used in aviation. For example, hydrogen fuel cells could be used to make electricity or through direct combustion as fuel. This means you could use electricity to power a smaller plane propeller or hydrogen fuel cells along with a regular jet engine to power non-propulsion systems on the plane to reduce emissions. Airbus and Boeing are already researching this last option.
Hydrogen is also a candidate to help decarbonise shipping. For example, hydrogen fuel cell-powered vessels and alternative fuels such as methanol or dimethyl ether could be used in dual-fuel engines and act as a propulsion.
However, it’s likely for the above reasons aviation and marine shipping sectors are most likely to be the last ones to decarbonise as they both need energy-dense fuels fully. At present, zero-carbon options for these fuels are not ideal.
As we’ve seen, most options for decarbonising transportation rely on EVs, which for long distances means regular charging stations and infrastructure along highways and routes or alternative fuels. Hydrogen or biofuels offer good solutions, but in the case of aeroplanes and shipping, they will require entirely new designs and vehicles to accommodate them. Although further research and innovation could see breakthroughs in these technologies, it looks like the road to decarbonising transportation still has a way to go.