What is our assessment?

Based on our analysis, blue hydrogen is feasible and ready to deploy, but there is little real-world evidence for its effectiveness or ability to scale. The expansion of this technology to replace current gray hydrogen production or to support the transition to a global hydrogen economy will perpetuate and possibly expand the use of fossil fuels. Because of this risk, we conclude that producing blue hydrogen is “Not Recommended.”

What is it?

Blue hydrogen production is an industrial process that produces hydrogen (H₂) from fossil fuels – either natural gas or coal – combined with carbon capture and storage (CCS) technology to reduce CO₂ emissions produced during the process. Today, most hydrogen is gray hydrogen made from natural gas without any CCS. The addition of CCS prevents the release of some of the CO₂ generated during the hydrogen production process; capturing, concentrating, and then storing it permanently underground. 

Does it work?

The technologies for making hydrogen from natural gas, predominantly steam methane reformation (SMR), are well established and have been used to produce hydrogen for close to a century. CCS technology is also available and currently deployed in multiple industrial and power generation applications. The SMR hydrogen production process generates GHG emissions from two sources: methane leaks from the gas used as feedstock and fuel used to power the production process, and GHG emissions from both the SMR process and combustion of gas (or other fuels) for energy, including CO₂, methane, nitrous oxide, and black carbon. CCS can be applied to capture CO₂ produced during the SMR process, for post-combustion capture of CO₂ from the plant’s energy use, or for both. Incorporating CCS to capture emissions from the hydrogen production process adds costs and increases energy use, but it could theoretically reduce CO₂ emissions by more than 90%. However, current adoption of blue hydrogen is very low – less than 1% of global hydrogen production – and there is little real-world evidence to support its effectiveness and scalability. The few commercial facilities currently in operation capture only about 60% or less of the emitted CO₂. Because CCS is energy-intensive, it requires more fuel to power the blue hydrogen production plant. This can also increase fugitive methane leaks due to increased gas-powered energy consumption. If implemented adequately, carbon storage can be permanent. The captured CO₂ can also be used as a chemical precursor for the manufacture of other products or for enhanced oil recovery; however, these post-capture uses of CO₂ emit GHGs, thereby reducing or eliminating the emissions reduction efficacy of CCS. Currently, only ~8% of CO₂ captured from blue hydrogen production is injected into dedicated geological storage, with the rest used in industry, enhanced oil recovery, and other applications. 

Why are we excited?

Hydrogen can be combusted as a zero-emissions fuel, used to store energy to produce electricity, or deployed as a feedstock in industrial, transportation, and energy systems. The production of any hydrogen type – blue, gray, or green hydrogen – could facilitate the expansion of hydrogen infrastructure and the development of the global hydrogen economy, which is an important step in scaling hydrogen. Blue hydrogen is more technologically ready and cheaper than green hydrogen, which is made from water using electrolysis powered by renewable energy. Blue hydrogen is more expensive to produce than gray hydrogen, but the cost per metric ton of CO₂ removed could be relatively low. Estimates range from US$60–110/t CO₂, although these costs are uncertain and, with lower CCS effectiveness, they could increase to ~US$260/t CO₂. If implemented with low fugitive methane emissions and high CCS efficiencies, blue hydrogen could substantially reduce emissions compared to current gray hydrogen production. The climate impact of scaling blue hydrogen could be high. Estimates and targets for blue hydrogen production by 2050 range from ~30–85 Mt hydrogen. At that scale, even modest emissions savings relative to gray hydrogen would have a climate impact above 0.09 Gt CO₂‑eq/yr by 2050. However, achieving this depends on the quality of the infrastructure and rate of technology scaling, both of which are unproven. 

Why are we concerned?

Currently, 6% of the world’s natural gas and 2% of its coal are used to make hydrogen. As hydrogen production ramps up, blue hydrogen – even though it reduces production emissions compared to gray hydrogen – would perpetuate and could even increase the global market for fossil fuels. If the future implementation of green hydrogen is set back, blue hydrogen could create a long-term dependence on fossil fuels. Furthermore, any hydrogen produced from natural gas leads to methane leaks, regardless of whether CO₂ is captured. Methane is a potent short-lived GHG, meaning its impact on climate warming is stronger in the near-term. This is why reducing methane emissions is an urgent emergency brake climate action. Building and expanding a new industry that relies on natural gas as both a feedstock and fuel, and which inevitably leaks methane, is counterproductive to solving the climate crisis. 

If and when there is a transition to a global hydrogen economy, blue hydrogen is a less effective climate solution than green hydrogen. Although this technology could be a transitional solution between gray and green hydrogen, blue hydrogen risks diverting resources away from green hydrogen development or ready-to-deploy renewable energy technologies, such as onshore wind or distributed solar PV. Expert opinions are mixed regarding the realistic level of avoided emissions that blue hydrogen may reach. Additionally, there is uncertainty around whether CCS can meet its technical potential at a reasonable cost.

What is our assessment?

Based on our analysis, vertical farms are not an effective climate solution. The tremendous energy use and embodied emissions of vertical farm operations outweigh any potential savings of reducing food miles or land expansion. Moreover, the ability of vertical farms to truly scale to be a meaningful part of the global food system is extremely limited. We therefore classify this as “Not Recommended” as an effective climate solution.

What is it?

Vertical farms are facilities that grow crops indoors, with multiple layers of plants stacked on top of each other, using artificial lights, large heating and cooling systems, humidity controls, water pumps, and complex building automation systems. In principle, vertical farms can dramatically shrink the land “footprint” of agriculture, and this could help reduce the need for agricultural land. Moreover, by growing crops closer to urban centers, vertical farms could potentially reduce “food miles” and the emissions related to food transport.

Does it work? 

The technology of growing some kinds of crops – especially greens and herbs – in indoor facilities is well developed, but there is no evidence to show that doing so can reduce GHG emissions compared to growing the same food on traditional farms. Theoretically, vertical farms could reduce emissions associated with agricultural land expansion and food transportation. However, the operation and construction of vertical farms require enormous amounts of energy and materials, all of which cause significant emissions. Vertical farms require artificial lighting (even with efficient LEDs, this is a considerable energy cost), heating, cooling, humidity control, air circulation, and water pumping – all of which require energy. Vertical farms could be powered by renewable sources; however, this is an inefficient method for reducing GHG emissions compared to using that renewable energy to replace fossil-fuel-powered electricity generation. Growing food closer to urban centers also does not meaningfully reduce emissions because emissions from “food miles” are only a small fraction of the life cycle emissions for most farmed foods. Recent research has found that the carbon footprint of lettuce grown in vertical farms can be 5.6 to 16.7 times greater than that of lettuce grown with traditional methods.

Why are we excited?

While vertical farms are not an effective strategy for reducing emissions, they may have some value for climate resilience and adaptation. Vertical farms offer a protected environment for crop growth and well-managed water use, and they can potentially shield plants from pests, diseases, and natural disasters. Moreover, the controlled environment can be adjusted to adapt to changing climate conditions, helping ensure continuous production and lowering the risks of crop loss.

Why are we concerned?

Vertical farms use enormous amounts of energy and material to grow a limited array of food, all at significant cost. That energy and material have a significant carbon emissions cost, no matter how efficient the technology becomes. On the whole, vertical farms appear to emit far more GHGs than traditional farms do. Moreover, vertical farms are expensive to build and operate, and are unlikely to play a major role in the world’s food system. At present, they are mainly used to grow high-priced greens, vegetables, herbs, and cannabis, which do not address the tremendous pressure points in the global food system to feed the world sustainably. There are also concerns about the future of the vertical farming business. While early efforts were funded by venture capital, vertical farming has struggled to become profitable, putting its future in doubt.
 

What is our assessment?

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.

What is it?

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. 

Does it work?

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. 

Why are we excited?

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. 

Why are we concerned?

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.

What is our assessment?

Because incineration of waste to produce electricity and/or heat does not reduce emissions in most circumstances, and it can displace or disincentivize other, more effective waste treatment practices, Deploying Waste to Energy is “Not Recommended” as a climate solution.

What is it?

Waste to energy (WTE) uses high temperature incineration (above 800^oC) of waste, including municipal solid waste (MSW), medical or hazardous waste, and waste biomass from agriculture and forestry, to generate electricity and/or heat. This energy production technology can be used to displace fossil fuel energy sources. However, like fossil fuels, the incineration process produces GHGs during combustion, primarily CO₂ and nitrous oxides, as well as ash and other pollutants as byproducts. WTE also diverts waste from landfills and open dumps, avoiding high-impact methane emissions from decomposing organic materials and pollution and health risks from inorganic or toxic materials. Globally, there are more than 1,700 WTE plants. According to the International Energy Agency (IEA) World Energy Balances, WTE from industrial and municipal waste accounted for less than 0.5% of global energy production in 2022. Around 62% of WTE plants are in Asia, 33% are in Europe, and 4.5% are in North America. Other waste to energy technologies, such as pyrolysis and gasification, which use heat to convert organic materials into various forms of syngas, are evaluated in other Drawdown Explorer solutions and not included here. 

Does it work?

The effectiveness of WTE for reducing GHG emissions when substituting for fossil fuels for heat and energy, while also avoiding landfill emissions, is highly variable. Effectiveness varies with waste type and quality, combustion characteristics, air pollution controls, alternative disposal methods, and the type of electricity generation that it displaces. WTE incineration is less energy efficient than natural gas or coal for producing electricity (20–30% for WTE compared to 40–60%), and relatively more waste must be burned to produce comparable amounts of energy. WTE incineration is also less energy efficient than pyrolysis (40–75%), gasification (40–60%), and even methane digestion (30–40%). In regions that incinerate large proportions of plastic waste, such as South Korea and China, emissions are higher than for landfilling the waste. For some waste streams in some regions, other treatment strategies such as recycling, composting, pyrolysis, gasification, or the production of biochar, bio-oils, or bio-bricks yield greater emissions reductions.

Why are we excited? 

WTE can reduce waste volumes by up to 90%. In high-income regions without available land for sanitary landfills with landfill gas capture systems (see Improve Landfill Management), incineration is a viable alternative for post-recycling, hazardous, industrial, or medical waste. However, incineration of these waste streams requires strict standards, advanced air pollution control systems, and continuous monitoring to minimize harmful emissions of toxic pollutants. 

Why are we concerned?

In almost all circumstances, incinerating waste to produce reliable electricity or heat is not an effective method for reducing GHG emissions. WTE plants require a steady stream of waste feedstock to ensure ideal combustion conditions for electricity and heat production. This can incentivize waste production and disincentivize alternative waste treatments that reduce emissions more effectively. For example, in the European Union (EU), where incineration is widely used, some countries need to import waste to maintain energy production. This offsets some or all of the potential climate benefit due to emissions during transport and may divert attention from better waste management solutions, such as regulations on packaging, recycling, and composting. In other countries, high incineration rates of MSW (above 30%) are correlated with declines in recycling rates. For example, in 2018, Japan incinerated over 80% of MSW while only 4.9% was recycled. Recent policy initiatives there now focus on increasing recycling, which effectively and consistently reduces emissions, and decreasing incineration through source separation of waste. According to one study, chemically recycling plastic waste rather than incinerating it saves 0.82 kg CO₂‑eq /kg of feedstock. 

WTE is a substantial source of toxic air pollution. Poorly constructed, unregulated incinerators generate air pollution and large amounts of ash that will need further treatment. Advanced air pollution control systems are required to minimize emissions of GHGs and pollutants, including particulate matter, sulfur dioxide, nitrogen oxides, carbon monoxide, other acid gases, heavy metals, and persistent organic pollutants like dioxins. Even in high-income countries with strict air quality standards, polluting incinerators are disproportionately sited in under-resourced communities, which exacerbates environmental justice issues. In the United States, 79% of incinerators are located in low-income or minority communities. 

Finally, WTE is the most expensive waste management method in most regions, largely due to high capital costs. In 2018, all countries using industrial incinerators for incinerating more than 10% of MSW were high-income, except China. The addition of necessary emission control and monitoring systems further increases costs, making WTE more expensive than methane digesters or landfills with gas capture systems.

What is our assessment?

Using CCS on fossil-fueled power plants will reduce electricity production emissions, but it is more expensive, more energy-intensive, and more polluting than readily available, cheaper, and cleaner alternatives like wind, solar, and geothermal. Based on this, and the risk that large-scale deployment of CCS on fossil-fueled power plants could drive continued production and use of coal and gas, we conclude that using CCS on fossil fuel power plants is “Not Recommended” as a climate solution.

What is it?

Carbon capture and storage (CCS) is a technology that reduces GHG emissions from fossil fuel-powered electricity generation facilities by selectively capturing CO₂ from the power plant’s exhaust flue, preventing it from entering the atmosphere. The captured CO₂ is then concentrated, compressed, and permanently stored underground. There are other commercially available CCS technologies, such as pre-combustion capture and oxy-fuel combustion, but these are used almost exclusively for industrial processes like gas processing and cannot be readily retrofitted to existing power plants. CCS can also be applied to capture CO₂ from other industrial facilities that generate emissions from fuel combustion or production processes, like cement or ethanol production plants, or from biomass energy power plants. Instead of permanent storage, captured CO₂ can also be used as a chemical precursor for the manufacture of other products or for enhanced oil recovery, but, compared with geologic storage, these post-capture uses of CO₂ emit GHGs, thereby reducing or eliminating the emissions reduction efficacy of CCS. 

Does it work?

The technology and chemistry for the selective capture of CO₂ from the exhaust of a power plant are effective. There are numerous chemical, membrane, and cryogenic methods for capturing CO₂, but monoethanolamine (MEA) is the predominant commercially available chemical absorbent currently in use in power plants with CCS. CO₂ capture efficiency varies with the type of reactive absorbent material and plant operations. Most CCS installations target 90% CO₂ capture rates, although actual capture rates are usually lower. CCS infrastructure is large, and the process of capturing CO₂ from power plant exhaust is complex, expensive, and energy-intensive. CCS requires the flue gas to be pumped to different parts of the power plant, the CO₂ to be captured and then separated from the sorbent material, and the concentrated CO₂ to be compressed for transport and storage. Energy for all these processes comes from the power plant. Various studies estimate CCS consumes at least 15–25% of the plant’s total generation capacity, with most of the energy used to separate the CO₂ and regenerate the sorbent material. 

CCS has been used in pilot studies and commercial operations in a few dozen coal and natural gas power plants since the late 1990s. Despite the functional effectiveness of the technology, use of CCS to reduce power plant emissions has not been broadly adopted, and most CCS projects initiated in the past three decades have failed or been discontinued. Based on various assessments and projections, deployment of CCS on power plants has consistently lagged behind its expected contribution to emissions reduction. There are currently only four power plants with CCS in operation in the world, less than 0.05% of the global fossil-fueled power plant fleet. According to a 2021 study, only 10% of proposed CCS projects for power plants have actually been implemented. Based on another study, 78% of all power plant and industrial manufacturing CCS pilot and demonstration plants with a project size greater than 0.3 Mt CO₂ /yr have been cancelled or put on hold. 

Why are we excited?

Globally, emissions from coal- and gas-fired power plants are still increasing, primarily in China and India, where large numbers of new thermal power plants have been built in the last two decades. Given the typical 30- to 45-year operational lifespan for coal and gas power plants, retrofitting these newer plants with CCS could substantially reduce their operational emissions while also allowing plant owners and investors to recover their investments. Installation of CCS to reduce emissions can also be prioritized for power plants located near places with geologic storage and where alternative electricity generation options are limited. There is a large amount of research underway to develop and test alternative carbon capture technologies, most aimed at increasing carbon capture efficiencies and reducing energy demands and costs. Other research on the factors contributing to the failure of most CCS projects to date may lead to the development of regulations and policies that require or incentivize the use of CCS for power plants, which could increase the current low implementation and success rates for this emissions reduction technology. 

Why are we concerned? 

While CCS can reduce the operational CO₂ emissions from fossil-fueled power plants, large-scale deployment of this technology will likely drive continued production and use of coal and gas. Even before fossil fuels are burned, extraction, transport, and processing generate substantial GHG emissions, particularly for gas. Therefore, in addition to perpetuating the fossil fuel industry, even 90% efficient CCS reduces only a fraction of the life cycle emissions from coal and gas. 

Widespread deployment of CCS in the electricity sector could also delay or crowd out deployment of wind, solar, and geothermal energy, slowing the clean energy transition that is already underway. Beyond these risks, the three-decade-long failure of power plant CCS to make the transition from pilot-scale science and technology to large-scale commercial deployment reflects its systemic problems and limitations. Unlike wind and solar energy, which have seen costs decline rapidly with development and deployment, CCS on power plants shows little evidence of a learning curve. It remains very expensive and very energy-intensive. A large-scale CCS demonstration project can cost more than US$1 billion to build and, in addition to its operational costs, CCS consumes at least 15–25% of the energy that the plant could otherwise sell to customers. CCS-related energy requirements could mean that a power company would need to build an additional power plant to compensate for reduced electricity deliveries from every four of its power plants equipped with CCS. 

Due to these high project risks and costs, as well as the lack of regulations and policies to require or support CCS on power plants, public and private investments in the technology have been falling. Despite all this, recent research shows that the vast majority of lobbying spending for government support of CCS comes from fossil fuel interests, which have publicly stated that they view the technology as a strategy to extend society’s use of fossil fuels. Finally, in contrast to most other climate solutions that provide other benefits to natural systems or human well-being, CCS on power plants does nothing to address or alleviate the current harm from toxic air pollution produced by fossil-fueled power plants.

What is our assessment?

Based on our analysis, cultivated meat is promising in its ability to reduce emissions from meat production, but the impact on a large scale remains unclear. Based on our assessment, we will “Keep Watching” this potential solution.

What is it?

Cultivated meat (also called lab-grown or cultured meat) is a cellular agriculture product that, when used to replace meat from livestock, can reduce emissions. Cultivated meat is developed through bioengineering. Its production uses sample cells from an animal, in addition to a medium that supports cell growth in a bioreactor. Energy is required to produce the ingredients for the growth medium and to run the bioreactor (e.g., for temperature control, the mixing processes, aeration).

Does it work? 

Since the development of cultivated meat is still in its infancy, there is limited evidence on its emissions savings potential from large-scale production. Preliminary estimates differ by an order of magnitude, depending on the energy source used in the lab environment. Using fossil energy sources, emissions generated from the production of 1 kg of cultivated meat could reach 25 kg CO₂‑eq. If renewable energy is used, emissions could be about 2 kg CO₂‑eq/kg of cultivated meat. By comparison, producing a kilogram of beef from livestock generates 80–100 kilograms CO₂‑eq, on average. Almost half of those emissions from livestock beef are in the form of methane. Producing pig meat and poultry meat generates about 12 kg and 10 kg CO₂‑eq, respectively. Based on these estimates, cultivated meat could substantially reduce the emissions of beef. Compared to pork and chicken, however, its emissions depend on the source of energy used during production.

Why are we excited?

The cultivated meat industry is fairly new but growing rapidly. The first cell-cultivated meat product was developed in 2013. In 2024, there were 155 companies involved in the industry, located across six continents, mostly based in the United States, Israel, the United Kingdom, and Singapore. Agriculture is responsible for about 22% of global GHG emissions, and raising livestock, especially beef, is particularly emissions-intensive. Therefore, cultivated meat has great potential to reduce related emissions as demand for meat continues to grow across the world. Cultivated meat enables the production of a large amount of meat from a single stem cell. This means that far fewer animals will be needed for meat production. Cultivated meat is also more efficient at converting feed into meat than chickens, which reduces emissions associated with feed production and demand for land.

Why are we concerned?

Concerns about cultivated meat include scalability, cost, and consumer acceptance. Because cultivated meat is still an emerging area of food science, the cost of production may be prohibitive at a large scale. Although cell culture is routinely performed in industrial and academic labs, creating the culture medium for mass-market production at competitive prices will require innovations and significant cost reductions. There are still many unknowns about the commercial potential of cultivated meat and whether consumers will accept the products. In 2024, companies began to move from research labs to larger facilities to start producing meat for consumers. Several countries now allow the sale of cultivated meat. In the United States, about one-third of adults find the concept of cultivated meat appealing, and only about 17% would be likely to purchase it, according to a poll conducted on behalf of the Good Food Institute. However, even substituting a fraction of the beef consumed in the United States with cultivated meat could have an important impact on reducing emissions. Cultivated meat is a novel food and may require consumer education and producer transparency on production methods and safeguards in order to become more widely accepted.

What is our assessment?

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.

What is it?

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.

Does it work?

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.

Why are we excited?

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.

Why are we concerned?

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.

What is our assessment?

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.”

What is it?

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.

Does it work?

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. 

Why are we excited?

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. 

Why are we concerned?

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.

What is our assessment?

Based on our analysis, the widespread use of bioplastics is challenged by their potential ecological risks and currently high costs. While bioplastics offer some environmental benefits in niche applications, their climate impact is inconsistent and hinges on feedstock type, manufacturing practices, and waste management. Therefore, we conclude that Deploy Bioplastics is a solution to “Keep Watching.”

What is it?

Bioplastics (also called biopolymers) are plastic alternatives made from renewable biological sources, such as corn, sugarcane, crop residues, or other plants, instead of fossil fuels. Bioplastics are produced by extracting sugars or starches from plants and converting them through chemical or biological processes into chemical building blocks that form the basic structure of plastics. Because plants absorb atmospheric CO₂ through photosynthesis, the carbon stored in bioplastics is considered biogenic, as it is already part of the natural carbon cycle. In contrast, petrochemical plastics are made by extracting and refining oil or natural gas, which releases new (formerly buried) carbon into the atmosphere. Bioplastics cut emissions by replacing fossil carbon feedstocks with biomass-based feedstocks. Some bioplastics are durable, non-biodegradable, chemically identical to traditional plastics (i.e., “drop-in” bioplastics), and recyclable. Others are biodegradable and can be designed to break down in compost. Emissions from bioplastics come from growing and processing biomass (which requires energy and land use), manufacturing the plastics, and managing their end-of-life waste. Bioplastics can achieve climate benefits when the emissions from production and end of life are kept low enough to realize the advantages of biogenic carbon.

Does it work?

The basic idea of bioplastics is scientifically and chemically sound, with their development and commercialization ongoing since the 1990s. Numerous studies support the effectiveness of bioplastics in reducing atmospheric CO₂ emissions from feedstock production and manufacturing stages compared to fossil-based plastics, particularly when made from sustainably sourced biomass under energy-efficient conditions and properly composted or recycled. However, other studies show bioplastics have inconsistent emissions reduction performance. Global adoption also remains limited, representing only about 0.5% of total plastics production (approximately 2–2.5 Mt out of 414 Mt, according to European Bioplastics). 

Why are we excited?

Bioplastics, particularly biologically derived and biodegradable polymers, have functional advantages in reducing fossil fuel dependence and mitigating plastic pollution. By sourcing raw materials from renewable biomass instead of petroleum (e.g., oil, natural gas), bioplastics can lower CO₂ emissions in the production stage, especially when accounting for biogenic carbon uptake during plant cultivation. Some types of bioplastics are interchangeable with traditional plastics and can be produced with existing plastic manufacturing systems, easing the transition. Compostable plastics simplify disposal in applications where contamination with food or organic waste occurs, enabling organic recycling and returning carbon and other nutrients to soil. Biodegradable bioplastics are also advantageous for products that are often discarded and may leak into the environment. Studies show that two widely used commercial bioplastics, polylactic acid (PLA) and polyhydroxybutyrate (PHB), biodegrade 60–80% in composting conditions within 28–30 days, while cellulose-based and starch-based plastics can fully degrade in soil and marine environments in 180 days and 50 days, respectively. These functional benefits, combined with potential additional benefits, such as soil enrichment and waste stream simplification, make bioplastics appealing in specific, targeted use cases. More broadly, they can significantly contribute to emissions reduction efforts in materials production when designed for circularity and supported by infrastructure that facilitates appropriate end-of-life waste treatment. 

Why are we concerned?

Despite their promise, bioplastics have several limitations as a viable climate solution, including relatively low emissions reduction potential and possible risks and adverse impacts from their large-scale deployment. Current production is low. To reach a meaningful 20–30% marketplace share by 2040, bioplastics would need to expand manufacturing by approximately 30% per year, nearly double the current pace. This could put pressure on land and food systems, since current bioplastics rely on food-based crops for industrial-level production. This raises sustainability concerns around food security and could potentially drive unintended land-use changes such as deforestation or cropland conversion. Furthermore, the effectiveness of reducing emissions by replacing conventional plastics with bioplastics is low and inconsistent. Some bioplastics produce more life cycle emissions than conventional plastics. The likely climate impact of replacing 20–30% of traditional plastics with bioplastics is <0.1 Gt CO₂‑eq/yr. End-of-life treatment is also a major challenge. Many bioplastics are incompatible with home composting and current recycling streams, and improperly composted or landfilled biodegradable bioplastics can emit methane. Finally, bioplastics remain 2–3 times more expensive than conventional plastics.

What is our assessment?

Based on our analysis, SMRs are a plausible and potentially impactful climate solution, but they are not yet ready for widespread deployment. The core technology is credible and carries significant potential for reducing GHG emissions. However, readiness, cost certainty, and deployment evidence are still lacking. For now, we will “Keep Watching” SMRs.

What is it?

Small modular nuclear reactors (SMRs) are advanced reactors that produce low-carbon electricity by harnessing the heat from nuclear fission, an established and well-understood physical process. The innovation of SMRs lies primarily in their design. Typically smaller than traditional reactors, with a capacity of less than 300 megawatts (MW), SMRs are factory-built for enhanced quality control. This design allows them to be delivered to installation sites more quickly and potentially at a lower cost compared to conventional reactors, which typically range in capacity from about 700 MW to over 1,600 MW. While SMRs are generally considered "utility-scale" in their capacity, their smaller size makes them a viable option for smaller-scale applications, such as large micro-grids. These reactors can be assembled in a modular fashion, allowing incremental capacity additions. Additionally, some SMR designs boast enhanced safety features, including passive cooling systems that can function without external power sources, reducing the risks associated with reactor overheating or meltdowns. Currently, several countries are planning the deployment of SMRs, particularly China and the United States. Given their modular nature, several African countries, such as Ghana, are also looking toward SMRs to address their energy access deficits. Based on current plans, the International Energy Agency expects several countries to have multiple SMRs installed and operational by around 2030.

Does it work?

The physics behind SMRs is sound, and their potential as low-carbon energy sources is also scientifically valid, as they do not emit GHG emissions during operation. Several pilot SMR projects have also been launched. SMRs have yet to move beyond the demonstration phase to widespread commercial adoption. No SMR is currently deployed at the scale necessary to reduce global emissions measurably. Furthermore, independent, peer-reviewed empirical data on long-term operational performance, scalability, and cost remain sparse. While several countries, including the United States, Hungary, China, and Ghana, have announced plans or are discussing deploying SMRs within the next decade, those plans are still in the preparatory stages.

Why are we excited?

SMRs have several features that make them appealing as a potential climate solution. If scaled appropriately, they could displace fossil-fuel-based power generation and reduce carbon emissions significantly. Projected deployment scenarios by the Nuclear Energy Agency suggest that by 2050, the global SMR market could reach 375 gigawatts of installed capacity, avoiding up to 15 Gt of cumulative CO₂ emissions. Their smaller size and modular nature reduce financial risk, making them potentially more accessible to developing countries or smaller utilities. They are also flexible in siting and can complement variable renewable energy sources like solar and wind by providing reliable baseload or backup power. Additionally, SMRs could help decarbonize hard-to-electrify sectors like process heat in industry or remote energy systems. These attributes have prompted excitement among proponents who see SMRs as a scalable, flexible, and resilient solution for emissions-free power. 

Why are we concerned?

Despite their promise, SMRs face several challenges that limit their readiness for large-scale deployment. Safety remains a concern – not necessarily because of design flaws, but because any nuclear reactor carries inherent risks. Waste disposal and the potential for proliferation of nuclear materials remain persistent issues. Regulatory hurdles are also significant, as existing frameworks are often geared toward conventional reactors and may slow the licensing of newer designs. The cost of SMRs is another outstanding question. Recent analyses by Wood Mackenzie suggest that SMRs could cost US$6,000 to US$8,000 per kilowatt of capacity, which is well above the costs of utility-scale solar (US$1,448) or onshore wind (US$2,098). Deployment timelines also pose a challenge. Given the urgency of climate action, technologies that cannot be deployed at scale within the next 10–15 years may offer limited near-term benefits. A recent study by the Institute for Energy Economics and Financial Analysis opines that SMRs are still too costly, too time-consuming to construct, and too risky to significantly impact the transition away from fossil fuels in the next decade. While peer-reviewed academic studies have been conducted, a comprehensive, independent evaluation of large-scale deployment remains absent.