What is our assessment?

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.”

What is it? 

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.

Does it work?

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.

Why are we excited?

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. 

Why are we concerned?

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.

What is our assessment?

Advanced geothermal systems (AGS) are emerging as one of the most promising technologies for reliable, utility-scale, zero-carbon energy that can complement wind and solar, strengthening grid resilience, and providing heat for district heating and industrial uses. The technology, which is built on an existing base of technical and industrial expertise and capacity, is advancing rapidly through major R&D efforts, pilot projects and, just recently, small scale commercial operations. While large-scale deployment is still in its early stages and challenges remain around cost, execution, and social acceptance, we expect meaningful progress by the 2030s. For now, we will “Keep Watching” this solution.

What is it?

Advanced geothermal systems (AGS) are a suite of renewable energy technologies that extract heat from deep within the Earth’s crust to generate electricity, provide high-temperature heat for industrial processes or district heating, and enable geothermal energy storage by storing heat underground. Unlike traditional geothermal systems that tap naturally occurring hot water or steam reservoirs, such as geysers or volcanic areas, AGS access geothermal heat by drilling into the earth, injecting and circulating water (or other fluids) through hot, dry rock formations underground, and then recovering the heated fluid or steam to generate electricity before reinjecting it back underground. Circulation of the water between the surface and the geothermal reservoir can be a in closed loop system, where the water or other fluid is contained within pipes throughout the heat exchange circulation cycle, or in an open loop, enhanced geothermal system (EGS) where the subsurface rocks are hydraulically fractured, or “fracked,” to increase permeability and allow water to flow between an injection well and a production well.

Does it work?

Electricity and heat production by an advanced geothermal power plant emits virtually no greenhouse gases. Analysis by the National Renewable Energy Laboratory showed that the median life cycle emissions from enhanced geothermal power plants were 32 g CO₂‑eq/kWh, just 6% of the median life cycle emissions from a natural gas power plant, with most of the emissions generated during construction rather than operation. Geothermal energy has been used for more than a century, but AGS that use the directional and horizontal drilling and hydraulic fracturing techniques developed by the oil and gas industry to access previously inaccessible underground heat resources are relatively new. To date, several small-scale and experimental AGS projects have successfully produced electricity, and in December 2025, the first commercial plant for electricity and heat production delivered electricity to the grid in Germany. 

Why are we excited?

Advanced geothermal energy systems are a potentially transformative climate solution for several reasons. First, they could massively expand clean energy availability. AGS can be deployed in almost any region with hot subsurface rocks. Experts estimate the Earth’s accessible geothermal resources are staggeringly large, and that tapping just 0.1% of the heat under our feet could meet global energy needs for millennia. If technology improvements continue, advanced geothermal could supply around 15% of the world’s electricity by 2050. Second, unlike solar and wind energy, advanced geothermal power plants produce steady baseload power, dispatchable power, and even energy storage. Currently, coal and gas power plants are commonly used to provide stability and backup power to electricity grids around the world. AGS can provide the same energy benefits, complementing wind and solar energy by providing firm capacity and grid stability services to a renewable-heavy electricity grid, without the harmful climate impacts. Third, AGS plants have a relatively small land footprint and can potentially be sited near demand centers (including repurposing old fossil plant sites), improving energy security for regions with limited solar or wind resources.

Recent technological breakthroughs have improved the prospects for AGS. The application of directional drilling and hydraulic fracturing techniques has produced higher fluid flow rates and extended reservoir life. This has dramatically increased the heat extraction per well, overcoming previous limitations and boosting the energy output and economics of AGS. Industry reports show drilling rates in hot rock have increased by 300–500% in the last few years, slashing upfront costs. A recent U.S. Department of Energy report projects that the cost of next-generation geothermal projects, including AGS, will fall below that of other baseload power sources such as nuclear and natural gas with carbon capture and storage (CCS) by 2035. Other projections suggest that geothermal electricity could drop to around US$50/MWh by the 2030s, competitive with other renewables and nuclear. Finally, AGS leverage a skilled workforce and supply chain from the oil and gas sector. The necessary drilling rigs, subsurface imaging, and engineering expertise already exist, which could help scale up AGS faster than entirely new industries.

Why are we concerned?

Despite its promise, AGS face several challenges that temper its near-term prospects. To bridge the gap from pilot stage to commercialization, the industry needs more demonstration projects, case studies of success, and greater public trust. This is challenging because advanced geothermal projects today have high upfront capital costs, primarily due to deep drilling and, for EGS, hydraulic stimulation expenses, as well as high operational costs. Current AGS electricity is also far more expensive than conventional renewables, often hundreds of dollars per MWh. Until these costs decline, the industry may struggle to attract the investment financing needed to scale up. Moreover, the geological uncertainty in any given project is high because limited geophysical data in many regions makes it hard to pinpoint the best spots to drill. Developers must invest in exploration with no guarantee of finding an adequate resource, so early projects carry a significant risk of cost overruns.

Safety and environmental concerns also pose challenges. In some types of geologies, enhanced geothermal systems, which use hydraulic fracturing to create the heat exchange reservoirs and circulate fluid underground, can trigger small earthquakes. Some EGS have been halted after local earthquakes caused alarm and minor damage. Because they use water and circulate hot brines, AGS could pose risks for groundwater contamination or water consumption in arid regions, although geothermal system designs that use closed-loop systems or non-potable water can avoid these problems. Finally, geothermal projects often face regulatory and logistical hurdles and lengthy permitting processes. In many countries, regulatory regimes and incentives have focused on solar, wind, and even nuclear, while geothermal energy (and especially AGS) has received comparatively little support. This means AGS developers may struggle with financing and grid access due to policy gaps or obstacles. 

What is our assessment?

There is strong evidence that green roofs sequester carbon and may reduce building energy consumption, although emissions reduction data are limited and vary with geography, roof design, and other factors. The potential climate impact of increasing green roofs is likely too small to be globally significant (>0.1 Gt CO₂‑eq/yr ). The solution, however, is considered “Worthwhile” because it can reduce energy use in buildings and sequester carbon while helping communities adapt to climate change and benefiting human health, the environment, and building owners.

What is it?

Vegetation planted on specially engineered rooftops sequesters CO₂ through photosynthesis and provides indirect cooling for buildings through evapotranspiration, reflecting heat back to the atmosphere, and shading (Shafique et al., 2020; Tan et al., 2023; U.S. EPA, 2025). This cooling plus the added insulation inherent in the design can reduce the air conditioning loads of the building, particularly compared to dark rooftop surfaces, and therefore reduce emissions from the electricity used to power cooling systems (He et al., 2023; Susca, 2019). Green roofs can also reduce heating energy use and corresponding GHG emissions due to the insulation that soils and plant matter provide (He et al., 2023; Susca, 2019). Green roofs are in use in all regions of the globe, but concentrated in high-income countries (Mihalakakou et al., 2023; Zhang & He et al., 2021). 

Does it work?

There is strong evidence that green roofs sequester carbon and can reduce the energy consumption and therefore emissions from cooling and heating buildings. Carbon sequestration by vegetation on green roofs has been documented in several studies (Getter et al., 2009; Konopka et al., 2021; Shafique et al., 2020; Tan et al., 2023). A study in Germany found that plants absorbed 141 g carbon/m²/yr (517 g CO₂ /m²/yr) over a 5-year period (Konopka et al., 2021). However, carbon sequestration rates are difficult to generalize due to variations in design, plant types, and climates (Getter et al., 2009; Shafique et al., 2020; Tan et al., 2023). 

Reported building energy savings from green roofs can range from negligible to 60% or more for cooling (He et al., 2023; Susca, 2019). For heating the savings can reach 45% or more, but some studies also show a roughly 10% increase in heating energy use with a green roof (He et al., 2023; Susca, 2019). The large variability in energy savings outcomes is due to differences in climate; existing insulation and other properties of buildings; green roof design, vegetation and maintenance practices; and measurement and modeling approaches (He et al., 2023; Mihalakakou et al., 2023; Susca, 2019). The highest energy savings potential has been calculated in dry-winter subtropical highlands for cooling and in humid subtropical climates for heating (He et al., 2023). Areas with short and mild winters are most likely to see heating energy use increase with green roofs, but these areas often have net energy savings when heating and cooling are combined, and most studies of green roofs show a reduction in heating energy use (He et al., 2023; Susca, 2019). 

When combined with the carbon sequestration effect of vegetation, green roofs appear to consistently reduce GHG emissions. 

Why are we excited?

Green roofs and other urban green spaces (see Manage & Increase Urban Trees) provide valuable climate adaptation, human health, environmental, and economic benefits. Green roofs can help cities adapt to climate change because the vegetation reduces heat exposure during extreme heat, while the soil and root systems absorb stormwater – thereby reducing runoff and flooding risks during extreme rainfall (Mihalakakou et al., 2023; Perivoliotis et al., 2023; U.S. EPA, 2025). Green roofs improve human health because vegetation filters the air and reduces noise transmission, and interactions with green spaces, including green roofs, have been shown to improve mental well-being (Knight et al., 2021; Mihalakakou et al., 2023; Perivoliotis et al., 2023; Zhuo et al., 2025). Green roofs can increase biodiversity and habitat and remove water pollution. They also can increase the property value of a building and prolong the longevity of the roof (Zhang & He, 2021).

Why are we concerned?

Increasing green roofs can be challenging due to high up-front cost, lack of supportive policies, structural and climate limitations, maintenance requirements, and lack of awareness. A green roof can cost substantially more up front than a conventional roof, and although it can save energy for cooling and heating, the returns on investment can be lengthy and savings may not be enough to fully offset the higher costs (Zhang & He, 2021). In addition, not all roofs can support vegetation, rooftop plants can struggle to survive in hot and dry climates, and green roofs may increase heating energy use in buildings in climates with short and mild winters (He et al., 2023; Mihalakakou et al., 2023; Susca, 2019; Zhang & He, 2021). A green roof also requires maintenance such as watering, plant care, weed control, pruning, and regular inspections (Green roof guide, n.d.). Finally, a lack of awareness is a major barrier to greater adoption (Zhang & He, 2021). We also noted a lack of measured, rather than modeled emissions reduction data and on current and potential green roof adoption globally. 

What is our assessment?

Based on our analysis, Improve Steel Production using green hydrogen and electric furnaces powered by clean electricity has the potential to significantly reduce emissions. However, while the individual technologies that are needed are mature and their combined use has been piloted, the process has not yet been adopted in a meaningful way. We will “Keep Watching” this solution, but it is not ready for widespread adoption.

What is it?

Currently, making steel from iron ore relies heavily on coal and other fossil fuels to provide heat and reducing agents (chemicals that remove oxygen from iron ore) (IEA, 2020; Ryan et al., 2020; Zhang et al., 2023). Improve Steel Production refers to using electric heat and hydrogen produced by electrolysis to reduce the iron ore (H₂-DRI) and electric arc furnaces (EAF) to melt the resulting iron and alloy it with carbon to make steel. The solution also requires the electricity used in these processes to include significant renewable energy or other low-carbon generation. The output is varying grades of steel with different degrees of hardness and brittleness determined by slight variations in carbon content. This solution does not include processes that rely on bioenergy or CCS, since the emissions from burning bioenergy contribute to climate change and CCS is not an effective climate solution.  

Does it work?

Replacing fossil fuels in steelmaking with H₂-DRI-EAF that uses electrolytic hydrogen and where all electricity comes from relatively clean sources results in significantly reduced emissions. Steel made today using fossil fuels for heat and as a reducing agent results in an estimated 1.8 t CO₂‑eq /t of steel (Bataille et al., 2021). By contrast, steel made using H₂-DRI-EAF and low-carbon electricity would generate an estimated 0.12 t CO₂‑eq /t of steel and is a more energy-efficient process (Bataille et al., 2021). EAF furnaces are already very common in steelmaking and for recycling existing steel, but are rarely combined with H₂-DRI (IEA, 2020; Devlin et al., 2023). Although H₂-DRI was first used on an industrial scale in 2001, that plant was shut down for economic and political reasons, and economics remain a barrier (Wang et al., 2026). Finally, technologies to make industrial hydrogen from electricity are mature (Bataille et al., 2021), but most hydrogen produced today is made from fossil fuels and is carbon-intensive. Active research is exploring other technologies that could become important for improving steel production in the future, most notably aqueous or molten oxide electrolysis, both of which use electricity to directly remove oxygen from iron ore, and can be combined with EAF to make steel (Bataille et al., 2021, Hubner Australia, n.d.).  

Why are we excited?

Steelmaking is classified as a hard-to-abate industry, and H₂-DRI-EAF powered by clean electricity is considered one of the best strategies for cutting emissions in this sector (Devlin et al., 2023, IEA, 2020; Bataille et al., 2021). The Net Zero Industry project forecasts that under an emissions-neutral steel scenario by 2050, roughly 40% of global steel production could depend on H₂-DRI-EAF, with the remainder consisting of recycled steel (47%), steelmaking with CCS (11%), or technologies not yet defined (2%) (Bataille et al., 2021; Net Zero Industry, n.d.). The impact is potentially significant, given that steelmaking accounted for an estimated 3.7 Gt of CO₂‑eq in 2019 (IEA, 2020). Improved steelmaking has the additional benefit of reducing air and land pollution, as burning coal releases fine particulate matter, heavy metals, and other pollutants. In China, steel production is the largest industrial source of air pollution (IEA, 2020). As demand for steel is expected to increase up to 30% by 2050 due to demand from India and other low- and middle-income countries, it is critical that new and existing production shift to cleaner, lower-emission technologies, and that policies supporting this shift be implemented.  

Why are we concerned?

While proposed low-emission steel projects have attracted significant attention from the press, many have since been canceled or put on hold (Milne, 2025; Russell, 2025; Wrede 2025). As of 2025, we could find references to only a few pilot facilities producing improved steel as we have defined it here (Leadit, 2025). The entire H₂-DRI-EAF process is considered to be at the large-scale prototype demonstration stage (Bataille et al., 2021). However, contributing technologies such as electrolytic hydrogen production and EAF are more mature, and H₂-DRI was first used on an industrial scale in 2001 (Wang et al., 2026). The higher cost of making low-emission steel is a significant barrier to industrial adoption and consumer demand (Devlin et al., 2023; McKinsey & Company, 2024). Electricity accounts for nearly half the cost of producing low-emission steel from iron ore (McKinsey & Company, 2024). 

To increase adoption, improved steel facilities need to be located in areas that can readily supply both iron ore and abundant low-carbon, low-cost electricity (McKinsey & Company, 2024). In areas such as China, where the electricity grid still relies heavily on fossil fuels, transitioning to H₂-DRI-EAF risks increasing emissions unless dedicated renewables are integrated into the project. To move this solution forward, new policies are needed to create an international market for low-emission steel (IEA, 2020). Meanwhile, existing steelmaking facilities typically have lifetimes of 25–40 years (IEA, 2020), which increases the likelihood of stranded assets or continued reliance on fossil fuels by 2050. Under its Sustainable Development Scenario, the IEA (2020) projected that, by 2050, only 12% of cumulative direct emissions reductions in steelmaking will be due to electrification and the use of hydrogen (the IEA considered emissions from electricity to be indirect). Reducing demand for steel, incremental efficiency gains, and CCS are expected to make up the bulk of cumulative direct emissions reductions, according to the IEA (2020) projections.

What is our assessment?

Based on our analysis, improving district heating for industry by integrating low-carbon heat sources has the potential to significantly reduce the use of fossil fuels and the emissions they generate. However, the lack of data, combined with the complexity of such projects and the growing interest in alternative decarbonization pathways, makes this a potential solution to “Keep Watching.”

What is it?

District heating systems consist of a network of underground pipes that distribute heat to a large number of buildings, including industrial buildings. In the industrial sector, district heating is used by light industries and for processes such as drying, paper making, food processing, as well as space heating and even heat-driven refrigeration (Bellevrat & West, 2018; Difs et al., 2009). Industry is well suited to district heating because it typically has steady and predictable heat demand throughout the year. Current district heating systems rely heavily on coal and natural gas for heat generation, often as part of combined heat and power generation (IEA, 2026). Low-carbon alternatives for district heating can include electric boilers, electric heat pumps, solar thermal, deep geothermal, and even waste heat from other industries (IEA, 2026; International Renewable Energy Agency [IRENA] et al., 2020). 

Does it work?

Shifting district heating for industry from conventional heat sources to low-carbon heat sources will significantly reduce emissions. Our analysis for district heating use by commercial and residential buildings shows that significant emissions can be avoided by shifting to electric boilers, heat pumps, and the use of waste heat (see Improve District Heating: Buildings). Similar outcomes are likely possible for industrial district heating use, and emissions reductions will increase as more renewables are integrated into the electricity systems used to power electric boilers and heat pumps. 

Why are we excited?

District heating for industry currently produces significant emissions. According to the IEA (2026), district heating and cooling for all applications accounted for roughly 5% of global energy consumption in 2024, and roughly 40% of the heat energy from district heating was delivered to industry IEA, 2022). China is a major adopter of district heating for industries, with the combustion of coal supplying much of that heat (IEA, 2026). The shift to renewable heat sources is likely to increase because both China and the EU have policies targeting the adoption of renewables in district heating (European Commission, 2022; IEA, 2026). Because district heating systems serve multiple buildings, a single project to replace fossil fuels with renewables can have a large impact. Such projects also have the benefit of reducing local air pollution. 

Why are we concerned?

Although simple on paper, replacing fossil fuel systems with lower-carbon alternatives in district heating systems can be an extended undertaking involving many stakeholders and years of planning (Lake et al., 2017; Werner, 2017). Some low-carbon options may not be suitable for industrial processes that require higher temperatures than those needed for space heating (Bellevrat et al., 2018). There is also a significant lack of publicly available data about how industry currently uses district heating and the opportunities and challenges involved in shifting to renewables. In the meantime, industrial heat pumps with higher temperature outputs are increasingly available and could become a low-carbon competitor to the use of a conventional district heating system (IEA, 2026).

What is our assessment?

Based on our analysis, decentralized composting is a “Worthwhile” solution that reduces GHG emissions while producing nutrient-rich products that improve soil health, support urban green spaces, and promote community involvement in circular waste management. 

What is it?

Decentralized composting reduces GHG emissions from landfills by diverting and locally processing OW. Composting is an aerobic biochemical process in which microorganisms break down OW into a nutrient-rich soil supplement. Since household and community waste generators are responsible for decentralized composting, this approach can also reduce transport emissions. Decentralized composting already supplements existing OW curbside collection networks in many countries, including Canada, Brazil, Sweden, India, Italy, the United States, and New Zealand (Alves et al., 2023; Bruni et al., 2020; Ricci-Jürgensen et al., 2020; Spector et al., 2026). Although on-farm composting can be part of a decentralized organic waste management system, we focus on home and community composting for this solution. 

Does it work?

There is clear evidence that aerobic decomposition from composting OW produces fewer GHG emissions than landfilling, which relies on anaerobic decomposition (Amuah et al., 2022; Manea et al., 2024) and emits methane, which is 27.9 times more effective at trapping heat than CO₂ (100-yr basis). Disposal of OW in landfills emits nearly 1.9 Gt CO₂ ‑eq (100-yr basis) of methane annually (International Energy Agency [IEA], 2024). Although composting produces CO₂, methane, and nitrous oxide, emissions can be an order of magnitude lower than landfilling (Ayilara et al., 2020; Cao et al, 2023; IEA, 2024; Nordahl et al., 2023). Widespread adoption of decentralized composting has the potential to reduce annual waste sector emissions, which accounted for 3.9% of total global GHG emissions in 2019 (Intergovernmental Panel on Climate Change [IPCC], 2023). Per-ton GHG emissions from home composting are comparable to those from centralized composting (Barrena & Sanchez, 2022; Bruni et al., 2020) although there is also evidence of lower emissions (González et al., 2024). Quantitative data on emissions from community composting sites is very limited (Sanchez et al., 2022), but still show significantly lower emissions than landfilling (de Boni et al., 2022). Most peer-reviewed literature on decentralized composting examines pilot programs with some additional case studies for commercial and institutional programs (Alves et al., 2023; de Souza & Drumond, 2022; Shen et al., 2025; Specter et al., 2026), so quantitative estimates of adoption, adoption trends, and overall climate impact are very scarce. 

Why are we excited?

Decentralized composting is affordable, supports urban green spaces, and fosters a local, circular economy with myriad socioeconomic benefits for individuals and local communities. Since it also reduces methane emissions from landfills, it also has potential to be an emergency brake solution although the global achievable impact is uncertain. Home and community composting rely on adaptable, low-cost methods that can be readily implemented and controlled to ensure high-quality compost products (Alves et al., 2023; Bruni et al., 2020; Institute for Local Self-Reliance [ILSR], n.d.; Platt, 2017; Platt & Fagundes, 2018). Decentralized composting costs less, requires less space, offers faster return on investment, and is more likely to result in compost application to soils than centralized composting (de Souza & Drumond, 2022; Spector et al., 2026), and compost quality can be as good as or better than compost produced in centralized facilities (Álvarez-Alonso et al. 2024; Alves et al., 2023; Sanchez, 2022). 

Compost use in home and community gardens or other urban green spaces is often a benefit of decentralized composting (Platt et al., 2022; Spector et al., 2026). Applying compost to soils improves soil health, nutrient supply, and water retention, and can potentially enhance carbon sequestration (Iraji et al., 2025; Martínez-Blanco et al., 2013). Reducing or eliminating collection and transportation of OW from where it’s generated to centralized facilities offers other cost and emissions savings as well (Sanchez, 2022; Shen et al 2025; Spector et al., 2026). 

Finally, decentralized composting programs stimulate local economies by supporting local organizations and fostering community (Alves et al., 2023). Community composting programs expand public awareness and education around the environmental benefits of diversion from landfills and compost application (de Souza & Drumond 2022; Shen et al., 2025; Spector et al., 2026). Well-managed community composting programs can also reduce rodent problems in urban areas (Hosain et al., 2022). Allowing for a diversity of co-existing waste processors, both centralized and decentralized, enhances the flexibility and resilience of an integrated waste collection and management system while supporting a local circular economy (Barrena & Sanchez, 2022; de Souza & Drumond, 2022).

Why are we concerned?

Successful decentralized composting requires careful source separation of OW from contaminants such as nonbiodegradable plastics, persistent monitoring of the composting process to ensure optimal conditions, and public acceptance and support. In general, home and community composting faces lower risks of contamination than centralized facilities due to better sorting (Bruni et al., 2020). Optimal composting requires carbon-rich woody biomass as well as nitrogen-rich food and yard waste, but securing sufficient carbon feedstocks can be challenging (Sanchez, 2022). In addition, smaller scale composting operations can struggle to maintain temperatures high enough to kill pathogens (Sanchez, 2022), though management practices can mitigate this risk (Bilsens Brolis & Platt, 2019; ILSR, n.d.). 

Poor management of decentralized composting programs can increase GHG emissions, odors, and safety risks, including increased rodent problems (Hosain et al., 2022), sparking community backlash. GHG emissions during composting can be minimized through precise management, especially of temperature and oxygen availability (Yasmin et al., 2022), emphasizing the importance of training and education in decentralized composting (Spector et al., 2026). Robust community outreach and education on the benefits of separating waste and safe composting methods are essential components of decentralized composting programs (Brown, 2015; Platt & Fagundes, 2018). Although community composters can generate revenue from selling compost products, direct funding through memberships or service contracts with communities and local governments results in more sustainable decentralized composting operations (Spector et al., 2026). Despite clear evidence that decentralized composting reduces GHG emissions, the lack of global adoption data and persistent social barriers limits our ability to estimate maximum achievable climate impact.

What is our assessment?

Based on our analysis, we find that fishing vessel efficiency improvements are ready to deploy and feasible, but probably have limited climate impact because the wild capture fisheries sector contributes a relatively small share of global GHG emissions. These improvements will likely provide long-term cost savings and added benefits for ecosystems and air quality. We conclude this climate solution is “Worthwhile.”

What is it?

Improving fishing vessel efficiency reduces CO₂ emissions by using gear, vessel, or operational changes that lower fuel use in wild capture fisheries. Vessel upgrades include propulsion-related changes, such as installation of more efficient engines, and non-propulsion-related alterations, such as modified bows and hulls that reduce drag. Changing to low-fuel-use gear to catch fish, when and where possible, can also reduce CO₂ emissions. Operational changes, such as speed reductions or route optimization, can likewise lead to more efficient fuel use.

Does it work?

Vessel efficiency improvements are expected to deliver substantial fuel savings. An estimated 60–90% of emissions in wild capture fisheries, which emit roughly 0.18 Gt CO₂‑eq/yr in total, likely result from fuel consumption. Speed reductions alone can reduce fuel use by up to 30%. Vessel modifications could provide fuel savings of up to 20% in small fishing vessels, which comprise roughly 86% of all motorized fishing vessels globally. Upgrading engines and other propulsion-related equipment can reduce fuel use by up to 30%. Gear switching, when viable, can also be highly effective at improving fuel use efficiency, particularly if the target species are typically caught using methods such as trawling, which has a high carbon footprint. 

Why are we excited?

The average emissions per metric ton of landed fish in wild capture fisheries have grown by over 20% since 1990, highlighting the need for efficiency improvements. Many of these improvements can be implemented without sacrificing fishing effort or opportunities, and some operational changes, such as reducing vessel speed, can be done without any new equipment. All changes reduce fuel use, saving fishers money over time and likely resulting in fewer emissions of harmful air pollutants, such as sulfur oxides and black carbon. Some upgrades could deliver additional benefits to air quality and ocean ecosystems. Cleaner engines can further reduce air pollution through more complete combustion of fuel, and gear changes could benefit seafloor ecosystems, which can be damaged from bottom fishing practices, such as trawling and dredging. Additionally, some fishing gear has high bycatch rates, and switching to gear that allows for more exclusive capture of target species can reduce waste.

Why are we concerned?

Even with widespread adoption, efficiency improvements that reduce fuel use are unlikely to have a major climate impact. Efficiency improvements could also inadvertently encourage increases in fishing effort, which would increase fuel use and offset emissions cuts. Initial costs to upgrade can be highly variable, but might be high in some cases and therefore not feasible for some fishers. Gear switching can result in lower fish catches, as some methods might not be as efficient. Some operational changes, such as reducing speeds, could lead to fishers arriving at fishing grounds late.

What is our assessment?

While Improve Aquaculture is unlikely to have a major climate impact, our assessment concludes that it is “Worthwhile” due to its ability to reduce pressure on wild fish stocks and terrestrial biomass, and because efficiency improvements made now are likely to scale into greater climate impact as the sector continues to expand.

What is it?

GHG emissions from aquaculture can be reduced by increasing the feed conversion efficiency of the cultured animals and decarbonizing on-farm energy use. Aquaculture – farming aquatic animals or plants for food or other purposes – is rapidly growing and now accounts for over half of the global production of aquatic animals, exceeding wild capture fisheries. Over 7% of human-consumed protein is aquaculture-produced. As this sector has grown, it has become increasingly reliant on external feed sources, with the share of non-fed aquaculture (e.g., bivalves that feed from the water column) dropping from nearly 40% in 2000 to 27% in 2022. Improving feed conversion ratios (FCR) – the amount of feed it takes to produce a given amount of biomass – can lower feed demand and reduce CO₂ and other GHG emissions tied to feed production and transport. FCRs can be improved by feed formulations that increase digestibility, genetic or breeding modifications to improve digestive efficiency in the cultured animal, species-specific feed formulations, and optimizing ration size and feeding frequency. At the same time, decarbonizing on-farm energy use can help reduce CO₂ emissions from common equipment, such as aerators and water pumps.

Does it work?

Interventions to improve feed and energy efficiency can reduce CO₂ emissions from aquaculture operations, although the potential achievable climate impact of these actions is currently unlikely to be globally meaningful (>0.1 Gt CO₂‑eq/yr ). Total annual emissions from aquaculture were estimated to be 0.26 Gt CO₂‑eq/yr in 2017, with nearly 60% of that attributed to feed production. Improving FCR is both plausible and effective, since it directly reduces the amount of food needed to cultivate fish and other species, thereby lowering emissions tied to feed production and transport. Between 1995 and 2007, improvements in FCR have ranged between 5 to 15% for a variety of species, including shrimp, salmon, carp, and tilapia.

Decarbonizing on-farm energy use can reduce equipment-related emissions, particularly in intensive systems that use energy for automated feeding systems, water temperature control, and circulation and aeration systems. In general, the potential impact of decarbonizing varies widely because on-farm energy use differs significantly across species and production systems. For instance, shrimp and prawn farming use nearly 20,000 MJ/t of live weight (LW), with over 75% from electricity, while bivalve production uses around 3,000 MJ/t of LW supplied largely by diesel.

Why are we excited?

Improving feed efficiency in aquaculture reduces demand for captured wild fish used in feed, reducing pressure on overfished stocks. It also lowers reliance on terrestrial biomass, such as soy, wheat, and rice, which come with additional land-use and emission costs. More efficient feeding can help reduce nutrient pollution, which can be responsible for high methane and nitrous oxide fluxes in some inland aquaculture systems. At the same time, decarbonizing on-farm energy use might ultimately lead to lower long-term operating costs and improved energy reliability.

Why are we concerned?

There are relatively few drawbacks associated with improving aquaculture. In the case of decarbonizing on-farm energy use, upfront costs could be high. For instance, installing solar panels or upgrading pumps can be financially challenging for small-scale operations. Energy use on farms can also vary throughout the day and night, which might not always align with renewable energy sources, like solar, without storage. While this solution focuses on reducing GHG emissions from existing aquaculture practices, it is important to recognize that aquaculture can be environmentally harmful and that impacts vary widely depending on how it is done, where it occurs, and which species are being cultivated.

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.