Author :
Maria Cecilia Pinto de Moura
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Fossil Fuels Must Go: Re-inventing US Transportation


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EDITORIAL UPDATE, 7-8-24: a previous version of this blog was updated to include information contained in the UCS report on Hydrogen-Powered Heavy-Duty Trucks.

We have over 284 million gasoline- and diesel-burning cars, trucks and buses on our roads. Together with other modes of transportation, our vehicles emit the most heat-trapping gases in the US economy: 28 percent, followed closely by the electricity sector. Carbon dioxide and methane (a short-lived but extremely powerful global warming gas) are emitted during the extraction, processing, storage, transportation and combustion of gasoline, diesel and other petroleum fuels used by our vehicles. To adjust the focus of this picture a little closer, just our passenger cars and light trucks contribute to a whopping 58 percent of total transportation emissions, placing our car-centric society in the fossil fuel spotlight.

Petroleum has accounted for more than 90 percent of transportation energy in the last 50 years. But even after decades of using almost exclusively petroleum, we are not locked into this way of powering our vehicles. A study from Union of Concerned Scientists (UCS), an update of a 2021 collaboration (here, here) with Evolved Energy Research (EER), shows that we can meet US climate goals and have a fossil-free economy by mid-century, including the petroleum-guzzling transportation sector. This blogpost will explore the results of this study for transportation.

The Inflation Reduction Act (IRA) and the Investment and Jobs Act (IIJA) contribute significantly towards the US’s 2030 climate targets (50-52% reduction of global warming emissions below 2005 levels) and exceed these targets by 2035. However, these policies fall short of our goals of decarbonizing the economy by 2050, mostly because the incentives expire in the early 2030’s. In our study we evaluate the benefits of bold additional investments across the entire economy that drive emissions to net zero by 2050.

In the transportation sector, the main strategies to reach these goals are electrification backed up by a renewable power grid, together with a sweeping expansion in public transit and land use that support a reduction in driving. Contrary to claims made by some pundits, this transition away from fossil fuels can be done at moderate cost, primarily with technologies that are commercially available today. There is no question that electrification is the future, and our study shows that with smart policies we can make the transition away from transportation powered by fossil fuels to one which is more reliable, faster, cleaner and fairer for everyone.

Vehicle electrification has received a huge boost with the recent advances in battery cost, range, performance and charging. In our study, by 2035 all new vehicles sold are either battery-electric vehicles (BEVs) or fuel-cell electric vehicles (FCEVs). BEVs will account for almost 95 percent of passenger cars sales and more than 70 percent of heavy-duty truck sales in 2035. This phaseout of internal combustion engines (ICEs) in vehicles is aligned with state policy goals and Advanced Clean Car II mandates around the country (California, New York, Virginia and others).

Electricity is undoubtedly the best choice of fuel in the transition, as it is a proven technology and a efficient way to propel vehicles of all types and sizes. An EV uses less energy than a gasoline car to cover the same number of miles, as electric motors are three to four times more efficient than internal combustion engines. Burning fuel to power wheels is an intrinsically inefficient business, compared to electric motors, and vehicles with an internal combustion engine waste an astonishing 75 to 85 percent of the energy pumped into their tanks.

To increase the global warming benefits of electrification and significantly reduce air pollution, electricity must be generated from renewable sources. Wind, solar, biomass and geothermal energy already make up more than 20 percent of our electricity today, and in the study this portion grows to more than 90 percent in 2050. The share of electricity in the economy for powering EVs and other transportation modes grows rapidly from less than 0.5 percent in 2021 to about 16 percent in 2050. As we move towards an electrified future, it is possible to create benefits for everyone, including a more resilient grid and cost savings for both utility customers and EV owners, with investments in the right areas, such as expanding energy storage and transmission infrastructure, balancing grid loads with smart charging and vehicle-grid integration.

Two critical points about electrification are that it must be accompanied by continued investments in charging infrastructure, and  EV batteries must be safely reused, repurposed, and recycled.

Today trucks make up just 10 percent of the US vehicle fleet but contribute a disproportionate 23 percent of global warming emissions in the transportation sector. Their contribution to local air pollution is also highly disproportionate, as heavy-duty vehicles are responsible for 45 percent of on-road nitrogen oxides (NOx) and 57 percent of on-road fine particulate matter (PM2.5) emissions.

Electrifying this fleet with BEVs is in most cases the best way to reduce emissions. Fuel cell technology is a worldwide trend that may be useful for some long-haul large trucks which cannot be easily electrified with batteries. By 2050, there will be over 300 million ZEVS on the road, and we assume that out of this total about 10 percent will use fuel cell technology. According to our modeling assumptions, the share of FCEVs is larger for trucks, and slightly more than one quarter of zero-emission trucks will be using fuel cells by then.

Despite its emission reduction potential, this technology comes with caveats. It is expensive and has limitations, as is described in this UCS report and blogpost. The net benefits of FCEVs depend on many factors, including if the electricity used to produce this hydrogen is fossil-free. Vehicles powered by hydrogen fuel cells convert hydrogen, pumped at a station, into electricity that fuels traction batteries to power the wheels. Currently, the vast majority of the hydrogen produced is not fossil-free and is associated with harmful health impacts. However, FCEVs fueled with hydrogen created from electrolysis powered renewable energy have lifecycle climate impacts similar to BEVs powered by renewable energy.

As was already mentioned, the US is a supremely car-centric society.  The vast majority of households—92 percent—own at least one car, and we built a highway network that exacerbates inequity and enables urban and suburban sprawl. As a result, the US transportation system is the most carbon-intensive among affluent countries. Our geography and land use choices have apparently locked us into this paradigm, but there are ways of getting people and goods around that don’t involve growth in vehicle miles traveled (VMT), and possibly even lead to a reduction in driving. We must invest in expanding public transportation and rail and delve into a major rethinking of how we design and expand our cities and rural areas, making them more pedestrian- and bike-friendly, more equitable and safer for everyone. See this UCS blogpost for a more comprehensive look at the important topic of transitioning to a clean and equitable transportation system.

We modeled a Low Energy Demand (LED) scenario where there are economywide demand reductions, with reduced driving being key in transportation. This scenario illustrates how it is possible to reach the same climate targets with a reduced level of technology and infrastructure investment, like a more manageable, slower rate of renewable deployment, electricity transmission, and storage build-out, a reduced demand for EV batteries and charging infrastructure, and reduced carbon capture and sequestration (CCS) and CO2 pipeline infrastructure. With this reduced energy demand, it is possible to save 18 percent of the economy’s demand for electricity relative to the scenario where there is no reduced driving (which is called the Net Zero scenario). This difference is enough to power more than 35 million homes.  Similarly, the amount of biofuels and hydrogen is reduced by approximately 15 percent each, and the amount of CCS is reduced by almost 20 percent, adding on even more cost savings as well as energy savings.

The driving reduction assumed are in approximate alignment with VMT reduction targets for light-duty vehicles being laid out in various states, which is approximately in the range of 10 to 30 percent (California). Taking into account the population growth in the next three decades estimated by the AEO, the 20 percent reduction in light-duty vehicles from the Net Zero scenario to the LED scenario translates to an approximate seven percent per capita reduction in driving from 2021 through 2050.

Pollution from fossil fuels is deadly. Fossil fuels not only bear the largest share of responsibility for global warming pollution, but bear a huge part of the responsibility for local pollution from their long supply chain and from the combustion of its products, with impacts on air, water, soil, ecosystems, and of course, people. Air pollution from burning fossil fuels has an especially pervasive influence on human health, with some of its worst health impacts having been definitively linked to fine particulate matter (PM2.5). These health impacts are disproportionately borne by disadvantaged communities.

It was beyond the scope of this study to estimate the reductions in criteria pollutants separately for each economic sector, but economywide clean energy investments reduce deadly PM2.5 by 13 percent and other key pollutants such as nitrogen oxides and sulfur dioxide by 77 and 90 percent, respectively. Since vehicles are the largest sources of PM2.5 and NO2 emissions, it is reasonable to assume that the transportation sector has the largest share of the contribution in the decrease of these pollutants in the next three decades. On the other hand, a large portion of SO2 emissions originates from burning sulfur-containing fossil fuels in power plants and some industrial processes, so the transition towards renewables and the phaseout of coal in the electricity sector by 2030 explains the huge drop in these emissions.

The avoided health costs of air pollution from a fossil-based energy system more than offset the modest net energy system costs of $46 billion associated with the study’s Net Zero scenario in just the year 2050. The reductions in PM2.5 avoid 32,000 to 73,000 deaths in just 2050, associated with savings in the $368 to $826 billion range, in the Net Zero scenario. In the LED scenario, a few thousand additional deaths per year are avoided, associated with additional savings of a few tens of billions, thus illustrating the potential health and financial benefits of reducing driving and expanding mobility options.

For the sake of comparison, we wanted to highlight that the 2050 net energy system cost of $46 billion is a fraction of the estimated avoided cost of climate damage from the three principal greenhouse gases (carbon dioxide, methane and nitrous oxide). Estimates based on the EPA’s social cost of carbon – which  includes impacts on human health from climate change, along with agricultural productivity, consequences of increased frequency and severity of natural disasters, disruption of energy systems, risk of conflict and other factors – show that under the IRA/IIJA, the avoided climate damage from reducing greenhouse gases to meet US climate targets amounts to over $400 billion by 2035. This grows to almost $1.3 trillion in the Net Zero scenario by 2050, an amount that dwarves the net cost of the energy transition away from fossil fuels.

With more EVs and more efficient vehicles on the road, along with energy savings from less overall driving, we can reduce the use of liquid fuels for the road, aviation and shipping sectors by almost 50 percent in 2035 and by 86 percent in 2050, relative to 2021.  

But while zero-emission technologies allowing for this drastic reduction are evolving rapidly, we will face the challenge of decarbonizing this remaining liquid fuel, predominantly from sectors for which electrification progresses more slowly, such as aviation. Jet fuel demand does not decrease much over time and accounts for the bulk of liquid fuels used in the transportation sector by 2050, over three-quarters of remaining liquid fuels. Liquid fuels for boats and ships make up a tiny share of the remaining liquid fuels, with ammonia considered a potential low carbon shipping fuel.

Aside from aviation and shipping, there will still be some legacy on-road ICE vehicles using liquid fuels in 2050. Sales of ICEs end in 2035 but cars last about 15 years and it will take more time to electrify some large trucks. Because of this lag, it is important to continue to improve the efficiency of ICEs and make sure their global warming and local emissions are as reduced as possible, thus complementing electrification. EPA’s recent rulemaking on multi-pollutant emission standards is a step in the right direction.

With rapid deployment of electric vehicles, improved vehicle efficiency and reduced driving, it is possible to cut liquid fuel use by almost half from 2021 to 2035 and by more than two-thirds from 2035 to 2050, or 86 percent from 2021 to 2050. The remaining liquid fuels in 2050 are from the hard-to-decarbonize sectors, with jet fuel accounting for more than three-quarters of this remainder

There are three major potential sources of liquid fuels to meet this remaining demand:

Biofuels with carbon capture and storage (BECCS) are currently an alternative to petroleum and can play a key role in decarbonizing most of this remaining portion of liquid fuels, However, production needs to be kept at a feasible scale, accompanied by improved farming practices and biofuel production technology which reduces pollution. Caution is required as the excessive use of feedstocks can lead to significant uncertainty because of the high cost, limited supply, and sustainability risks associated with diverting vegetable oil from food uses.
A small volume of synthetic fuels made with hydrogen produced from renewable electricity and carbon makes sense only for hard-to-electrify applications, since it takes more energy to produce a liquid fuel than to use the electricity directly to power an EV.
A very small amount of petroleum may still be consumed in applications where biofuels and synthetic fuels are not available, but this continued use of petroleum-based fuels will require equivalent carbon dioxide removals elsewhere to offset any remaining emissions. It is key to stress that carbon removal technologies are not aligned with the objective of replacing all fossil-based transportation fuel with cleaner alternatives as quickly as possible, and are not free of substantial risks, yet are used in the EER model to reflect the current understanding that various forms of carbon capture may be required to offset the remaining emissions so as to reach net-zero emissions in 2050.

Biofuels are likely to be the lion’s share of the mix of these three potential sources, but this mix is highly uncertain and will depend on technology choices and policies.

It is possible for the US to phase out fossil fuels in the entire economy in a cost-effective way. Replacing fossil fuels with clean energy is the primary requirement for meeting our climate targets and vastly reducing toxic local pollution, thereby improving the health of millions of people in the country.

In the transportation sector, the largest user of fossil fuels in the US, we show that the strategies consist primarily of the direct electrification of vehicles, accompanied by a safe and reliable renewable power grid and a transition to an equitable transportation system where public transit, expanded mobility options and a decrease in driving are front and center. These non-technological societal changes that lower energy demand are key in reducing the extensive infrastructure build-up needed in the transition, while also allowing climate goals to be met by 2050.

The IRA and the IIJA are a significant step forward. They provide incentives and tax credits for buying EVs including used vehicles, for producing hydrogen, biofuels and sustainable jet fuel, and include several programs that can help advance environmental justice priorities. However, the investments expire in the early 2030s and must be complemented with additional strategies that achieve net zero global warming emissions by 2050. It is important to add that these policies also include some harmful provisions, such as expanding leasing for fossil fuel extraction and generous credits for carbon capture and storage, all of which could delay a phase-out of fossil fuels.

We urgently need the political will to make the right investments to accelerate this transition to a clean and equitable transportation system. All this must be achieved in the quickly narrowing window of time that remains to avoid the worst climate change impacts. At the same time, we must counter the powerful and well-funded efforts from the fossil fuel industry, sharply focused on its profitability and shareholders. Moreover, the fossil-fuel industry’s strategy has been centered for decades on a broad disinformation and well-funded campaign with the objective of throwing a wrench into the clean energy transition and continuing to produce fossil fuels.

All this must be achieved with justice goals at the forefront. Decision-makers at all government levels, both in the public and private spheres, must commit to the development of fossil fuel phaseout plans that ensure affected communities and workers will have a voice in decisions. With community engagement, consumer awareness, coordinated investments and much commitment and resolution, we can work together to re-invent our transportation system and help address climate change and the health impacts caused by the pollution from the toxic fossil fuel industry.


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