Replacing fossil-fuel-powered irrigation pumps with electric pumps powered by the grid can reduce emissions in most regions of the world. Electric irrigation pumps, which can also be powered by on-site clean energy, are more efficient than fossil fuel pumps. They are already cost-competitive and widely used, and adoption is increasing. Their emissions benefits will continue to grow as irrigation expands and the emissions intensity of the electrical grid falls. However, based on current grid emissions intensity, the climate impact of using electric pumps for agricultural irrigation is not globally meaningful (<0.1 Gt CO₂‑eq/yr ). Despite its modest climate impact, our assessment finds that deploying electric irrigation pumps is "Worthwhile".
Based on our analysis, deploying electric irrigation pumps will reduce emissions but will not provide a globally significant climate impact (>0.1 Gt CO₂‑eq/yr ), even under high adoption scenarios, until electrical grid emissions decline further. Therefore, this potential climate solution is “Worthwhile.”
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | Yes |
| Impact | Is it big enough to matter? | No |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | Yes |
This solution reduces emissions from irrigation by replacing pumps powered by natural gas, diesel, propane, or gasoline with electric pumps. Irrigation is the practice of adding water to croplands or pastures to reduce crop water stress and increase productivity. Pumps are used on some irrigated croplands to extract groundwater, transport surface water, and pressurize water for application through sprinklers or drip irrigation systems. Electric pumps have much higher motor efficiencies (~88%) than fossil fuel pumps (~21–31%), so pump switching reduces the energy required to pump the same amount of water. The extent to which emissions are reduced depends on the emissions intensity of the electrical grid mix. Electric pumps reduce emissions when the emissions intensity of the grid is below ~0.75 kg CO₂‑eq /kWh, or when they are powered by on-site solar or wind energy. In some places, additional emissions reductions can be achieved through Improving Irrigation Water Use Efficiency.
The efficiency and emissions benefits of electric pumps over fossil fuel pumps are well established. On-farm pumping emissions, currently estimated at approximately 0.2 Gt CO₂‑eq/yr, could feasibly be eliminated if all fossil fuel pumps are replaced with electric pumps and electrical grid emissions reach net-zero, or if they are powered by on-farm solar or wind energy. However, the climate impact of electric pump adoption today would be much lower, as electricity generation still produces substantial emissions. Under current conditions, replacing a diesel pump with an electric pump will reduce emissions in most, but not all, places around the world.
Electric pumps can reliably reduce emissions, are already cost-competitive and widely used, and adoption is increasing. Irrigation is a major energy user, and its energy use is increasing as irrigated areas expand. These trends are expected to continue in the coming decades as climate change exacerbates heat and water stress and agricultural production intensifies in low- and middle-income countries. Coupled with ongoing reductions in electrical grid emissions intensity, the potential climate benefits of this solution are growing.
Electric pump adoption can also be geographically targeted, as just five countries (China, India, the United States, Pakistan, and Iran) account for almost 70% of irrigation energy use. Areas with high groundwater reliance can also be targeted, as groundwater pumping accounts for 89% of irrigation energy use.
Pump switching also provides additional benefits, such as lowering long-term energy costs for farmers and reducing air pollution from on-farm fossil fuel use. Access to the electrical grid is the primary technical barrier to electric pump adoption, but small-scale solar installations can be used where grid connectivity is limited. Powering pumps with on-site solar also eliminates operational emissions, reduces the load on the electrical grid, and insulates farmers from variability in energy costs.
The climate impacts of pump switching are highly dependent on the emissions factor of the electrical grid. A large share of the potential reduction in fossil fuel pumping is located in India and China, which currently have relatively high electrical grid emissions intensities. Under the current grid mix, we estimate that pump switching in these countries will result in only modest benefits or a small increase in emissions.
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Avery Driscoll, Ph.D.
Christina Swanson, Ph.D.
Heather McDiarmid, Ph.D.
James Gerber, Ph.D.
Corn ethanol, an alcohol made by fermenting corn grain, is the most produced and used biofuel in the United States. The U.S. Renewable Fuel Standard requires that corn ethanol be blended with gasoline for the intended purpose of reducing transportation emissions. Ethanol is a useful vehicle fuel additive that improves engine performance and reduces air pollution. However, life cycle emissions analyses show that corn ethanol does not reduce GHG emissions as claimed and, more likely, increases emissions by 24% compared to gasoline alone. One-third of the corn grown in the U.S. is now used to produce more than 15 billion gallons of ethanol per year. This huge demand for corn has increased prices and driven the conversion of unfarmed land and natural ecosystems. The higher demand for corn also led to more fertilizer use on farms, resulting in increased pollution and nitrous oxide emissions. Based on these life cycle analyses, we conclude that using corn ethanol is "Not Recommended" as a climate solution.
The use of corn ethanol as a transportation biofuel, which has led to the expansion and intensification of corn production, does not reduce GHG emissions compared to gasoline. Based on this finding, using corn ethanol is not a plausible approach for reducing emissions and is “Not Recommended” as a climate solution.
| Plausible | Could it work? | No |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | No |
| Impact | Is it big enough to matter? | No |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
Corn ethanol is a liquid biofuel that is blended with gasoline to displace a fraction of the petroleum-based fuel with a renewable fuel derived from plants. Proponents claim that blending corn ethanol with gasoline reduces emissions because the CO₂ produced from combusting the ethanol is offset, or balanced out, by the atmospheric CO₂ absorbed by the corn plant during growth. Corn ethanol is made from corn grain by breaking down the starch in the kernels into sugar and then fermenting it into a liquid. In the United States, the world leader in biofuel production, almost 90% of biofuel is corn ethanol. Most gasoline now sold in the U.S. contains about 10% corn ethanol, and, in 2025, the Renewable Fuel Standard (RFS) program requires production of more than 15 billion gallons of this biofuel. Currently, it is primarily made from corn kernels; the technology for producing biomass-derived ethanol from other, non-edible parts of the corn plant is not yet commercially viable. Brazil is the second-largest producer of ethanol, but uses sugarcane as a feedstock.
The Renewable Fuel Standard requires that the life cycle emissions from corn ethanol be at least 20% lower than those of conventional gasoline. However, based on comprehensive life cycle emissions analyses, using corn ethanol does not reduce emissions compared to gasoline. The main reasons for this are that the production of corn and processing it into ethanol generate large amounts of emissions, including from land conversion, fertilizer-related nitrous oxide emissions, and the industrial process of fermenting the corn into ethanol. The most prominent recent study reported that corn ethanol life cycle emissions were, at best, no less than gasoline and, more likely, were 24% higher. Corn ethanol is also more emissions-intensive than ethanol made from other plants, like sugar cane.
Ethanol has been used as a transportation fuel, including as a blend with gasoline, for more than a century. It boosts the octane number of fuel, improves engine performance and fuel economy, and reduces emissions of harmful pollutants like unburned hydrocarbons, nitrogen oxides, and particulates. Ethanol has also been used to replace other harmful and polluting gasoline additives, including lead and methyl tert-butyl ether (MTBE). Ethanol produced from non-edible biological feedstocks with lower production emissions, such as switchgrass or cellulose from crop residues, has the potential to reduce emissions.
The Renewable Fuel Standard (RFS) program requires that biofuels be blended into the transportation fuel supply at annually increasing increments. The United States now uses one-third of its corn to generate more than 15 billion gallons of ethanol per year. Not only does this mandated program not reduce emissions (it more likely increases emissions), but it also consumes corn that could otherwise be used for food or animal feed. The increased demand for corn for ethanol has increased corn prices, which in turn have contributed to the conversion of grasslands and semi-natural ecosystems to grow more corn. When grasslands, woodlands, or other natural ecosystems are plowed and converted to cropland, the carbon stored in the vegetation and soil is emitted to the atmosphere. Between 2008 and 2016, the conversion of 1.8 Mha of natural and semi-natural land in the U.S. released about 400 million metric tons of CO₂ from vegetation and soil. The increased corn production also increased the application of synthetic fertilizers, which has increased nitrate leaching, phosphorus runoff, and emissions of nitrous oxide, a powerful GHG (see Improve Nutrient Management). These problems are particularly severe in the U.S. Midwest and the Mississippi River drainage.
Broda, M., Yelle, D. J., & Serwańska, K. (2022). Bioethanol production from lignocellulosic biomass—challenges and solutions. Molecules, 27(24), 8717. Link to source: https://www.mdpi.com/1420-3049/27/24/8717
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Ciolkosz, D. (2024). Fuel Ethanol: Hero or Villain? Penn State Extension. Link to source: https://extension.psu.edu/fuel-ethanol-hero-or-villain
Douglas, L. (2022). U.S. corn-based ethanol worse for the climate than gasoline, study finds. Reuters. Link to source: https://www.reuters.com/business/environment/us-corn-based-ethanol-worse-climate-than-gasoline-study-finds-2022-02-14/
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EPA (U.S. Environmental Protection Agency) (2025b). Lifecycle Greenhouse Gas Results. Link to source: https://www.epa.gov/fuels-registration-reporting-and-compliance-help/lifecycle-greenhouse-gas-results
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Green hydrogen is an emissions-free fuel produced by using renewable electricity to split water into hydrogen and oxygen. For aviation and long-haul trucking, green hydrogen can be used either directly in fuel cells or combusted in modified engines, offering a potential pathway to deep emissions reductions. It generates no CO₂ at the point of use, and when produced with clean power, life-cycle emissions can be near zero. However, green hydrogen faces major barriers in terms of energy intensity, infrastructure needs, cost, and vehicle redesign. We will “Keep Watching” Mobilize Green Hydrogen for Aviation and Trucking due to its high potential impact, even though it is not yet ready for widespread deployment.
Based on our analysis, green hydrogen holds long-term potential in sectors that are difficult to decarbonize, particularly long-haul aviation and freight trucking. It is technologically feasible, but currently hampered by high costs, severe infrastructure gaps, and limited commercial readiness. While it is unlikely to be deployed at scale this decade, we will “Keep Watching” green hydrogen as innovation and policy evolve.
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | No |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | Yes |
| Impact | Is it big enough to matter? | Yes |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
Green hydrogen is a clean, emissions-free liquid fuel produced through electrolysis powered by renewable energy that can replace fossil fuels in some transportation sectors. Unlike hydrogen from fossil fuels (gray or blue hydrogen), green hydrogen generates no CO₂ emissions during production. For transportation, green hydrogen can be used in two main ways: (1) in fuel cell electric vehicles (FCEVs) to generate electricity onboard and power electric motors, or (2) combusted in specially designed hydrogen combustion engines or turbines. For aviation, liquid hydrogen may fuel aircraft engines directly, be used to produce synthetic jet fuels, or power fuel cell airplanes. For long-haul trucking, hydrogen can replace diesel by powering fuel cell trucks, which offer long range and fast refueling.
Green hydrogen is being produced and used in pilot projects and select transportation initiatives globally. Hydrogen combustion engines and fuel cells are currently in use and have been shown to reduce emissions compared to fossil fuels. For aviation, aircraft manufacturers, such as Airbus, have hydrogen-powered planes in development, with test flights expected by 2030, but it could be several decades before they are put into commercial use. In heavy-duty trucking, several major automakers, including Toyota and Hyundai, have already commercialized hydrogen trucks in limited markets, such as China and Japan.
Green hydrogen is one of the few near-zero-emission fuels with the potential to decarbonize aviation and long-haul trucking, where battery-electric solutions currently face range and weight constraints. If produced using abundant, low-cost renewables, green hydrogen could significantly cut emissions in sectors responsible for nearly 15% of global transport emissions. In aviation, hydrogen-based fuels like e-kerosene could save around five million tons of CO₂ per year in Europe by 2030. In trucking, hydrogen fuel cell vehicles are beginning to roll out but remain a niche market. Looking ahead, hydrogen has strong potential: by 2050, it could meet up to 30% of energy demand in long-haul trucking and significantly reduce aviation emissions, particularly for short- and medium-haul flights, but it will have to compete with advances in battery-electric options. Hydrogen enables fast refueling and long range, making it a strong candidate for freight and intercity applications. Additionally, investment in green hydrogen infrastructure could unlock cross-sectoral benefits, supporting decarbonization of industry, power, and potentially heating. As electrolyzer costs fall and renewable power expands, the economics and emissions profile of green hydrogen are likely to improve.
Despite its promise, green hydrogen for transport faces significant technical, economic, and logistical hurdles. Electrolysis is energy-intensive, and green hydrogen production is still expensive (US$300–600/t CO₂ avoided for trucking and US$500–1500/t CO₂ for aviation), making it much more costly than diesel or jet fuel but comparable to sustainable aviation fuel today. It is also less energy-dense by volume than other fuels, requiring complex transportation and storage (especially for aviation, where cryogenic tanks are needed) and limiting payload capacity. In addition to producing contrails, hydrogen leakage, though not a GHG, can contribute to indirect global warming effects. There are also safety concerns related to flammability and explosiveness, and a complete overhaul of transportation and refueling infrastructure is needed for both aviation and trucking. Green hydrogen requires entirely new infrastructure for production, storage, and distribution, including refueling stations for trucks and specialized handling systems for liquid or compressed hydrogen at each airport the airplane uses. The absence of this infrastructure creates a major barrier to adoption in aviation and long-haul trucking, where fuel logistics, safety standards, and scale are critical for commercial viability. Hydrogen remains a niche fuel due to its low energy density per volume, the need for cryogenic storage in aviation, limited refueling infrastructure, and high cost. While technically viable, major deployment for aviation and trucking is still nascent. Without a clear business case or strong policy incentives, uptake will remain limited in the near term.
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International Energy Agency. (2019). The Future of hydrogen – analysis. IEA. Link to source: https://www.iea.org/reports/the-future-of-hydrogen
International Renewable Energy Agency. (2022). Green hydrogen for industry: A guide to policy making. Link to source: https://www.irena.org/publications/2022/Mar/Green-Hydrogen-for-Industry
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Sustainable aviation fuel (SAF) is a low-carbon alternative to conventional jet fuel. It is made from renewable feedstocks, including waste oils, agricultural residues, and renewable electricity. However, when combustion emissions are considered, SAF does not consistently reduce emissions when compared to conventional fuels. SAF is already in use in commercial flights at low blending levels. Advantages of SAF include its compatibility with existing aircraft and fueling infrastructure. Disadvantages include limited feedstock availability, high costs, variable climate benefits depending on production methods, and challenges in scaling up supply to meet global demand. We will “Keep Watching” SAF as part of a broader portfolio of aviation decarbonization strategies.
Based on our analysis, sustainable aviation fuel (SAF) has the potential to reduce emissions in the aviation sector, particularly for long-haul flights where few alternatives exist. However, pathways with the lowest emissions are not yet cost-effective and face significant challenges to scaling production due to feedstock constraints, land conversion pressure, and the need to meet robust sustainability standards. Based on our assessment, SAF is a climate solution to “Keep Watching.”
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | No |
| Impact | Is it big enough to matter? | ? |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
Sustainable aviation fuel (SAF) is a low-carbon alternative to conventional jet fuel that uses non-petroleum feedstocks such as waste oils, agricultural residues, and municipal solid waste. SAF is produced through chemical processes that convert these feedstocks into fuels that meet the same technical standards as fossil-based jet fuel, allowing them to be blended and used in existing aircraft engines and fueling infrastructure without modification. As of 2025, existing SAFs are only approved for use in blends; no SAF is yet certified for 100% use in commercial aircraft (also known as “neat SAF”) for passenger flights.
Life-cycle emissions vary widely depending on the feedstock and production pathway. Multiple SAF production pathways – such as hydroprocessed esters and fatty acids (HEFA), Fischer-Tropsch synthesis (FT), and alcohol-to-jet (ATJ) – have been approved by international aviation standards bodies. However, as of 2025, the HEFA pathway (which uses vegetable oils, waste oils, or fats) is the only commercially deployed method to produce significant amounts of SAF.
While some SAFs could achieve low emissions, others, especially those using food crops or poorly regulated waste streams, deliver uncertain climate benefits or can even increase emissions compared to conventional fuels. (We include emissions from burning biomass and biofuels, using default Intergovernmental Panel on Climate Change [IPCC] stationary combustion emission factors for each feedstock. See the Drawdown Explorer primer on “Effectiveness” of solutions.) Others, such as FT pathways, which use municipal solid waste or agricultural waste and residues, have the greatest potential for emissions reduction.
Real-world use of SAF is already underway: over 450,000 commercial flights have flown using SAF blends as of early 2025. SAF is currently being supplied at major airports in Europe, the United States, and Asia, with dozens of airlines integrating SAF into operations or entering offtake agreements. However, SAF supplies less than 0.5% of global jet fuel use.
Sustainable aviation fuels may reduce contrails, potentially significantly reducing aviation’s climate impact. SAF can be used in existing aircraft and fueling systems without requiring new infrastructure or major redesigns. This makes it one of the few ready-to-deploy solutions for long-haul and international flights, which are difficult to electrify or replace. SAF production from waste oils and residues can deliver additional benefits, such as reduced methane emissions from organic waste streams and improved waste management. Growing policy support, rising carbon prices, and airline demand are accelerating development.
Despite its promise, SAF faces significant limitations and challenges that could constrain its impact and scalability. In the United States, soybean oil is one of the most commonly used feedstocks for HEFA SAF, and its production faces similar land use and ecological risks and constraints as corn ethanol. Whereas in Europe, waste oils and fats are more commonly used. Measurement, reporting, and verification of actual emissions reductions can be complex, especially when land-use change, indirect emissions, or supply chain impacts are involved.
Due to limited feedstock availability, SAF is highly unlikely to meet the ambitious 2050 goals set by industry organizations and government institutions. Effective SAFs must be combined with other strategies, like demand reduction and new aircraft technologies, to achieve substantial emissions reductions.
Another major concern is cost. Current SAF prices are substantially higher than fossil jet fuel, ranging from US$300 to over US$1,500 per ton of CO₂ avoided, depending on the pathway. Without strong policy support, this cost premium poses a barrier to widespread adoption.
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