What is our assessment?

Based on our analysis, blue hydrogen is ready to deploy and feasible, but there is mixed consensus and limited data on its effectiveness in reducing emissions. Its climate impact has the potential to be high, but only if adopted effectively and at a large scale, both of which are currently unproven. If deployed correctly, this technology could serve as an interim solution to reduce gray hydrogen emissions while progress is made on scaling and reducing the costs of green hydrogen. Based on our assessment, we will “Keep Watching” this potential solution.

What is it?

Hydrogen is a fuel that can be used in place of fossil fuels in industrial, transportation, and energy systems. To deploy hydrogen as an energy source or feedstock, it first needs to be extracted from other compounds. Each “color” is an informal term specifying hydrogen produced through a unique hydrogen production path, each with different associated supply chains, processes, and energy GHG emissions. Gray hydrogen, which uses natural gas as the source of hydrogen atoms and electricity, is the most produced and has high production emissions, estimated at 10–12 t CO₂-eq/t hydrogen on a 100-yr basis. One way to reduce emissions is by switching to blue hydrogen, which still uses fossil fuels but also uses CCS technologies to prevent the release of some of the CO₂ generated during production. Blue hydrogen has the potential to be a lower-emission source of energy relative to gray hydrogen or direct fossil fuel combustion.

Does it work?

Blue hydrogen is a plausible way to reduce emissions from gray hydrogen production. However, expert opinions are mixed on the magnitude of emissions that can be abated by producing blue hydrogen in place of gray hydrogen. The effectiveness of emissions reduction hinges on two main factors: the rate at which upstream methane leaks and carbon capture rates, both of which are challenging to predict on a global scale. There is uncertainty around these performance metrics and the ability to effectively store and transport captured CO₂ at scale. Due to low current adoption, there is little real-world data to answer these questions. As of 2023, blue hydrogen comprised <1% of worldwide hydrogen production. While adding carbon capture to gray hydrogen production should help prevent emissions, there is limited evidence for both effectiveness and the ability to scale of this technology.

Why are we excited?

Compared to other types of low-carbon hydrogen, including green hydrogen produced from electrolysis powered by renewable energy, blue hydrogen is a technologically developed and lower-cost option. Without a currently viable and cost-effective alternative to gray hydrogen that does not use fossil fuels, blue hydrogen can be a near-term option to facilitate the transition to a global hydrogen economy. Expert estimates of cost per emissions avoided range widely, but the International Energy Agency (IEA) estimates US$60–85/t CO₂ for lower carbon capture rates (55–70%) and US$85–110/t CO₂ for higher carbon capture rates (>90%). However, these costs are uncertain: with lower estimates of effectiveness, the cost could increase to ~US$260/t CO₂, including the cost to transport and store CO₂. If implemented with low GHG fugitive emissions and high CCS efficiencies, blue hydrogen can reduce emissions by more than 60% relative to current gray hydrogen production on a 100-yr CO₂‑eq basis. In this case, 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 (3 t CO₂‑eq/t hydrogen, 20-yr basis) 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?

While it has some advantages, blue hydrogen is still a less effective solution than green hydrogen, while costing more than gray hydrogen. Though it could be useful for near-term energy decarbonization, this risks taking resources away from renewable energy and green hydrogen development while perpetuating and increasing fossil fuel use. The infrastructure required to scale hydrogen-based energy is expensive and will require technical advances and policy incentives to be competitive with fossil fuels. There are mixed expert opinions about the realistic level of avoided emissions that blue hydrogen may reach. The theoretical worst-performing blue hydrogen plants (low capture rates, high methane leaks, high-emission electricity sources) have been predicted to lead to more emissions on a near-term basis than direct natural gas combustion. Additionally, there is uncertainty around whether CCS can meet its technical potential at a reasonable cost. While experts predict >95% carbon capture rates are possible, facilities currently in operation capture less than this target, some less than 60% of all emitted carbon. For blue hydrogen to be feasible and scalable, CO₂ transport and storage need to be low-emitting, stable, and available. Only ~8% of CO₂ currently captured from blue hydrogen production is injected in dedicated storage, with the rest used in industry, enhanced oil recovery, and other applications. Finally, an understudied risk is hydrogen leaks. Hydrogen transport and storage require larger volumes than fossil fuels, increasing the risk of leaks. Hydrogen has an indirect planet-warming effect by increasing the levels of other atmospheric GHGs. At scale, the IEA estimates that high hydrogen leak rates could contribute 0.1 Gt CO₂-eq/yr in emissions, potentially canceling out any positive climate impacts.

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?

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 one kilogram of cultivated meat could reach 25 kilograms CO₂‑eq. If renewable energy is used, emissions could be about two kilograms CO₂‑eq per kilogram 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 kilograms and 10 kilograms of 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. There are only two countries that allow the sale of cultivated meat: Singapore and the United States. Within 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) is a promising climate mitigation solution for reducing emissions in the aviation sector, particularly for long-haul flights where few alternatives exist. However, it is not yet cost-effective and faces significant challenges to scaling production due to severe feedstock restraints, land use pressure, and the need to meet robust sustainability standards. Based on our assessment, we will “Keep Watching” this potential solution.

What is it?

Sustainable aviation fuel (SAF) is a low-carbon alternative to conventional jet fuel that reduces life-cycle greenhouse gas emissions from fuel production by using only non-petroleum feedstocks such as waste oils, agricultural residues, and municipal solid waste. It is usually produced using renewable electricity and captured CO₂. 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. All SAFs approved by ASTM International, the body that sets fuel standards for aviation, are certified only 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?

The basic idea of sustainable aviation fuel is technologically sound and supported by decades of research into low-carbon fuel alternatives for aviation. 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, and several have been demonstrated at commercial scale. 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. While current production remains limited (less than 0.5% of global jet fuel supply), government mandates, tax credits, and airline demand are driving the need for rapid scale-up. SAF is considered one of the most evidence-backed and immediately deployable climate solutions for reducing aviation emissions.

Why are we excited?

Sustainable aviation fuel offers several compelling advantages that make it a potential pathway for reducing aviation emissions. By reducing emissions 60-70% per ton compared to jet fuel, SAF could potentially avoid 0.1–0.2 Gt CO₂/yr by 2050. It can also reduce contrails. 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 also deliver benefits such as reduced methane emissions from organic waste streams and improved waste management. SAF offers a potentially scalable, technically feasible route to emissions reductions in a sector with few alternatives. Growing policy support, rising carbon prices, and airline demand are accelerating development. 

Why are we concerned?

Despite its promise, sustainable aviation fuel faces significant limitations, risks, and challenges that could constrain its impact and scalability. First, supply is a critical constraint. Due to limited feedstock availability, SAF is highly unlikely to be able to meet the ambitious 2050 goals set by ICAO, ReFuelEU Aviation, and other industry organizations, associations, and governmental institutions. This means that SAF must be combined with other strategies, like demand reduction and new aircraft technologies, to achieve full decarbonization. There are also major ecological and social risks, including competition for land and feedstocks that could displace food production or degrade ecosystems, as well as unequal access to the benefits of SAF deployment. Scaling synthetic SAF (e-fuels) requires vast amounts of clean electricity, water, and CO₂ – raising concerns about resource use and trade-offs with other sectors. 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 t CO₂ avoided, depending on the pathway. Without strong policy support, this cost premium poses a barrier to widespread adoption. Additionally, life-cycle emissions reductions vary widely depending on the feedstock and production pathway. While some SAFs (e.g., e-fuels using renewable electricity) can achieve near-zero emissions, others, especially those using food crops or poorly regulated waste streams, may deliver modest or uncertain climate benefits. Measurement, reporting, and verification of actual emissions reductions can be complex, especially when land-use change, indirect emissions, or supply chain impacts are involved. SAF combustion still contributes to climate impacts from contrails (albeit reduced compared to jet fuel), nitrogen oxides, and soot.

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 million tons (Mt) out of 414 Mt, according to the organization 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.