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.

What is our assessment?

Based on our analysis, nuclear fusion is a promising alternative form of electricity generation, but it is still at a theoretical stage and will not be ready for large-scale deployment within the next 10–15 years, when it could have the most impact on meeting global climate targets. We will “Keep Watching” this potential climate solution.

What is it?

Nuclear fusion is the process by which two individual elements are fused together into a single larger element using high pressure and temperature; this reaction releases large amounts of energy. This is the same reaction that happens in stars such as the sun. The energy from the fusion reaction can then be harnessed to produce electricity without emitting GHGs. Nuclear fusion power plants are best suited for centralized, large-scale generation (500 MW–1.2 GW of electricity output).

Does it work?

Nuclear fusion experiments have been carried out that prove the scientific principle is sound. However, only in recent years have experiments succeeded in producing more energy than was needed to initiate and sustain the fusion reaction. There have been no nuclear fusion power plants built to date, and it is unlikely that nuclear fusion–powered electricity generation will be ready for deployment before 2050.

Why are we excited?

Nuclear fusion energy offers several advantages as a solution to climate change, including high power density, the ability to deliver “firm” power (i.e., power that can be relied upon to meet demand when needed), and no GHG emissions. In addition, the most commonly used fuel for nuclear fusion – hydrogen – is readily accessible, there is no risk of a nuclear meltdown, and the process produces relatively little nuclear waste, meaning the risk of nuclear proliferation is almost nonexistent. Some research suggests that nuclear fusion could provide up to 15% of total electricity production either by replacing existing centralized power plants (e.g., oil and gas, coal, nuclear fission) that have reached end-of-life or to satisfy growing demand for electricity as access and electrification increase.

Why are we concerned?

Nuclear fusion is not considered remotely close to being ready to deploy as a climate solution. It faces many technical challenges, including uncertainties related to fusion reactor design and optimal fuel types. The costs for nuclear fusion–produced electricity are highly uncertain and are expected to grow compared to existing estimates. Current estimates for nuclear fusion energy costs exceed US$150/MWh, nearly double the 2020 price per MWh for other energy sources. There are also large uncertainties about the policy environment for nuclear fusion plants, which could hinder both development and deployment. Currently, projections suggest that nuclear fusion reactors could be introduced between 2050 and 2060. This means that even under optimistic conditions, nuclear fusion is unlikely to make a significant contribution to meeting 2050 emissions reduction targets. 

What is our assessment?

Based on our analysis, improved ruminant breeding is one of the few promising solutions for reducing enteric methane production from the many millions of ruminants, including those managed on pasture and rangeland. However, it is not a climate solution that will yield quick results, nor is it ready for large-scale deployment at this time. Instead, it should be considered a wise mid- to long-term climate investment that we will “Keep Watching.”

What is it?

Selective breeding can produce ruminant livestock, such as cattle, goats, and sheep, that produce less enteric methane during digestion. Enteric methane represents 21% of humanity’s methane emissions, equivalent to 2.9 Gt CO₂‑eq/yr. Enteric methane is produced by microbes in the digestive system – primarily in the rumen, which is the first stomach compartment – and not by ruminants themselves, but its production is a symptom of inefficient digestion by the animal. Therefore, breeding for more efficient use of food by ruminants can reduce enteric methane emissions, while also potentially increasing meat and milk production. 

Does it work? 

Selective breeding of ruminants for reduced enteric methane production has been shown to be effective. One 10-year pilot breeding program resulted in a 12% methane reduction in animals born in the last generation. Other studies have reported emissions reductions ranging from 4 to 45 percent. The effect can be cumulative, with greater reductions in enteric methane production with every selected generation of ruminants. 

Why are we excited?

Despite their disproportionate climate impact, ruminant meat and dairy products are in high demand. Any strategy that can reduce methane emissions per kilogram of meat or milk could, if broadly adopted, yield globally meaningful reductions in methane emissions (>0.1 Gt CO₂‑eq per year). A major advantage of this selective breeding approach is that it is suitable for both confined and grazing ruminants. The vast majority of ruminant animals spend all or part of their lives on pasture or rangeland. In contrast, feed additives, which can also reduce enteric methane production, are only suitable for confined animals. In addition, there is some evidence that this solution could increase the meat and milk productivity of ruminants by capturing energy from feed and forages that would otherwise have been lost as enteric methane.

Why are we concerned?

Breeding ruminants to reduce enteric methane production is not a climate solution that will show quick results. It will require prolonged testing using expensive measurement equipment on thousands of animals and selective breeding for each breed of each ruminant livestock species over many generations. Some researchers say that decade-long breeding programs will be required. Other than a few research projects, however, the current adoption of selective breeding for methane reduction is very low. Furthermore, selective breeding focused only on methane reduction could result in the loss of other desirable traits, such as productivity or adaptation to local conditions and farming systems. It is also possible that reducing enteric methane emissions per kilogram of milk or meat may not necessarily reduce total emissions if, for example, farmers or ranchers increase their herd sizes. Finally, there is the concern that improved ruminant breeding could be used as a smokescreen to divert attention from the importance of reducing consumption of ruminant meat and milk products in the diets of wealthy countries and reducing food waste of ruminant products.

What is our assessment?

Based on our analysis, feed additives are a promising technology that could yield globally meaningful reductions in methane emissions. A few, including 3-NOP, are just on the threshold of commercial adoption and may be widely used by confined ruminant producers in the coming years. The current use of feed additives is low, and the effectiveness of most feed additive compounds is not well-documented. Consequently, wide-scale adoption is largely confined to confined livestock in high-income countries. Based on our assessment, we will “Keep Watching” this potential solution.

What is it?

Feed additives are a diverse group of natural and synthetic compounds that, when fed daily, can reduce enteric methane production in ruminant livestock, including cattle, sheep, and goats. Enteric methane from livestock is the source of 21% of humanity’s methane emissions, or 2.9 Gt CO₂‑eq/yr. Feed additives reduce enteric methane production by suppressing the activity of microbes in the digestive system. 3-NOP (3-nitrooxypropanol) is a synthetic that inhibits an enzyme involved in enteric methane production.

Does it work?

More than 170 different feed additives have been developed and tested so far, but only a few of them have been studied enough to offer predictable outcomes and proper doses. Methane reductions from these well-studied additives typically range from 10-30%. The feed additive 3-NOP, the first compound approved for commercial use, reduces enteric methane by an average of 32.5%. A second feed additive derived from active compounds found in Asparagopsis seaweed has shown promising results in some studies and has recently received regulatory approval in two countries. In addition, because different feed additives use different mechanisms to suppress enteric methane production, it’s possible that multiple additives can be used together to achieve greater methane reductions. The great majority of other additives are not yet ready for widespread adoption due to a lack of understanding of effectiveness, side effects on cattle and humans who consume milk from treated cattle, and other concerns.

Why are we excited?

Ruminants are a major source of methane emissions, yet ruminant meat and dairy products are in high demand. Therefore, any strategy that can reduce methane emissions per kilogram of meat or milk is potentially very valuable and, if broadly adopted, could yield globally meaningful reductions in methane emissions (>0.1 Gt CO₂‑eq per year). The feed additive 3-NOP, first approved for commercial use in two countries in 2021, is now legal in 55 countries. Research on other feed additives is active and generally well-supported with funding from philanthropic and investment sources. Although current use of feed additives is very low, successful research and pilot studies, increasing regulatory approvals, and strong positive interest from the livestock industry suggest that wider-scale adoption of this emissions reduction technology could occur quickly. In addition to potential emissions reduction benefits, some additives offer other benefits such as increased productivity and parasite control.

Why are we concerned?

Because they must be fed daily as a supplement to a concentrated feed, use of feed additives is limited to ruminants managed under confined conditions. Most of the billions of ruminant animals today are raised or managed in extensive grazing or pastoralist systems, often in small herds in remote areas. This makes use of feed additives infeasible, although some research is underway to develop methane-reducing compounds that could be added to water troughs instead of to feed. Feed additives are also costly. Though they may be cost-effective in terms of dollars per ton of CO₂‑eq reduced, the cost of additives themselves would likely be prohibitive for smallholders and pastoralists in low-income countries. These limitations mean that feed additives, as currently under development, are only suitable for a subset of total ruminant livestock – those that are raised in confinement systems in wealthy countries. The great majority of feed additives are not yet ready for widespread adoption due to a lack of understanding of effectiveness, side effects on cattle and humans who consume milk from treated cattle, and other concerns. There are also other challenges, including regulatory issues, public acceptance, and effects on livestock and human health. There is also concern that feed additives could be used to divert attention from the importance of reducing ruminant meat and milk products in the diets of wealthy countries and reducing food waste of ruminant products.

What is our assessment? 

Based on our analysis, micro wind turbines (MWTs) are a promising technology for reducing emissions, but given the limited potential for global adoption and variable financial viability, they do not meet our threshold for global climate solutions (<0.1 Gt CO₂‑eq/yr ). Despite the low climate impact and high costs, Deploy Micro Wind Turbines is an important solution for achieving energy equity. Based on our assessment, we will “Keep Watching” this potential solution.

What is it? 

MWTs are small-scale turbines that rely on natural wind to generate electricity, charge batteries, or power equipment. Specific definitions for MWTs vary from country to country. Our analysis assessed energy production and GHG emissions reduction potential for wind turbines rated to generate a maximum of 100 kW of electrical power. MWTs are actively used for a variety of applications, including telecommunications, lighting, and agriculture. The total installed capacity for MWTs globally as of 2023 is nearly 1.8 GW or 0.002% of utility-scale onshore wind capacity. MWTs are most commonly used in rural settings.

Does it work? 

When connected to a regional or national electricity grid, MWTs can reduce baseline electricity grid emissions by reducing reliance on fossil fuel energy sources. Off-grid MWTs, which accounted for more than 90% of commercial sales in 2019, help electrify industrial and agricultural processes that otherwise may have been powered by fossil fuels, such as diesel or natural gas. Energy production from MWTs is highly dependent on the availability of consistent wind speeds, with the majority of turbines requiring an average wind speed of around 5 m/s to generate electricity. As long as sufficient wind resources are available, MWTs are effective at producing electricity to meet local energy demand and reduce reliance on fossil fuels.

Why are we excited? 

MWTs reduce reliance on fossil fuels for electricity generation, whether they are connected to an electric grid or isolated for local energy use. For grid-connected systems, more available renewable energy sources reduce the need for fossil fuel–based energy generation to meet demand. MWTs isolated from the electricity grid still reduce the local carbon footprint of a household, farm, or commercial building. Globally, the average household consumes approximately 17,000 kWh of electricity annually. Depending on the size of the turbine, local wind energy can produce 1,000–20,000 kWh/yr. Fluctuations in wind speed throughout the day and year can lead to unreliable power output, but this risk can be reduced by integrating batteries or hybrid electricity generation systems, such as combining wind and solar photovoltaics (PV). In addition to emissions reduction, MWTs are crucial tools for expanding electricity access worldwide. Since MWTs can operate independently of an electric grid, they can electrify rural areas where transmission lines are nonexistent or challenging to install. For example, many populations in Africa live in remote areas that could be well-served by installing MWTs to power telecommunications and other local electrification needs. Increasing interest in smart energy systems and Internet of Things technologies presents promising future applications for MWTs.

Why are we concerned? 

While MWTs show potential for expanding electrification, they have a number of limitations compared to other small-scale renewable energy technologies, like solar photovoltaics. First, real-world performance due to wind speed variability and turbulence at installation sites can be unpredictable and is often substantially lower than manufacturers’ power ratings. Second, life-cycle emissions from manufacturing and installation can be more than five times higher for small-scale wind than for large, multi-MW turbines. Energy payback times – the time period for the MWT to generate enough clean energy to offset the energy used during manufacturing and installation – can be long, sometimes exceeding the 20– to 25-year lifetime of the turbine. Third, MWTs are expensive, with up-front costs ranging from approximately US$3,000/kW to more than US$10,000/kW. Even after including financial incentives to partially offset high upfront costs, the levelized cost of electricity (LCOE) for residential MWTs in the United States was estimated at US$0.28/kWh. Not only was this higher than average U.S. residential electricity rates (US$0.1–0.24/kWh), but it was also more than double the LCOE for residential solar PV (US$0.12/kWh). Finally, noise pollution and vibration are environmental concerns for the wide-scale adoption of MWTs in urban areas. In addition, MWT performance can be poor in urban and suburban areas because buildings and other obstacles disrupt airflow. There is a general consensus in the scientific community and commercial market that MWTs are worthwhile electricity sources for many agricultural and industrial applications where cost is less prohibitive, but they remain a niche technology due to uncertain global economic viability and lack of reliable power generation in suburban and urban areas.

What is our assessment?

Based on our analysis, boosting appliance and equipment efficiency is a promising strategy for reducing GHG emissions, but significant leaps in efficiency and shifts in user behavior are needed to counteract the rebound effect and realize its impact. This potential climate solution is “Worthwhile.”

What is it?

Appliance and equipment efficiency typically refers to larger devices in residential buildings that run on electricity, such as refrigerators, freezers, washing machines, dishwashers, dryers, and televisions. Energy-efficient appliances or equipment consume less electricity when operated than do inefficient devices. Therefore, boosting appliance efficiency reduces the CO₂, methane, and nitrous oxide emissions from electricity generation. As of 2022, the energy consumed by household appliances globally was more than twice the total energy used to cool both residential and nonresidential buildings, and about half the energy used for heating. To drive higher efficiency for these devices, various countries have established regional energy efficiency standards, rating systems, and labeling programs. Currently, homeowners can readily access a variety of options on the appliance market, and less efficient devices can easily be replaced. However, income levels, especially in low- and middle-income countries, may affect people’s actual ability to purchase certain appliances, although these devices are increasingly becoming cheaper.

Does it work?

Improving the efficiency of appliances and equipment functionally reduces the energy required to run these devices. Various field studies have demonstrated the effect of efficiency gains on lowering electricity consumption. However, the rise in appliance ownership per household and the growing total number of households have offset the collective climate impact expected from efficiency improvements. Globally, the number of households grew from about 1.5 billion in 2000 to 2.2 billion in 2021. Considering the concurrent increase in the global average units owned per household, the number of appliances in use has essentially doubled over the same period. For example, we estimate that over two decades, the number of televisions owned grew from about 1.4 to 2.8 billion units, refrigerators grew from 0.9 to 1.7 billion units, and washing machines grew from about 0.6 to 1.1 billion units. This growth resulted in rising electricity consumption by appliances annually, from 2,880 TWh in 2000 to 5,734 TWh in 2022, which translates to a 99% global increase, largely driven by the Asia-Pacific region.

Why are we excited?

Boosting appliance and equipment efficiency allows homeowners to realize operational cost savings as a result of lower electricity consumption and utility bills. Compared with less efficient devices, using appliances with higher efficiency ratings functionally reduces peak electricity demand, alleviating strain on the electric grid. The advent of smart devices and the Internet of Things (IoT) also helps to automate the operation of these appliances, optimizing their runtime while minimizing the energy consumed. Initial purchasing costs are also declining, making efficient appliances more accessible and affordable. 

Access to high-efficiency appliances also yields additional benefits. For example, access to energy-efficient refrigerators and freezers means that food waste can be minimized with less energy, leading to better food security. Similarly, multimedia equipment, such as television sets, offers access to critical information. Further cuts in GHG emissions are also possible as the electric grid transitions to renewable energy sources.

Why are we concerned?

Despite the potential benefits, the efficiency improvements in household appliances and equipment have not effectively translated into a positive climate impact. This is largely due to the significant rebound effect, or the increase in appliances owned by households as these devices become cheaper and more efficient. Considering the role of appliances in providing a greater quality of life, limiting the increase in appliance purchases is dismissible. The markets for appliances and equipment in many countries also still consist of pre-owned devices, which are less efficient. Some countries, such as Ghana, have established legislation to prevent the importation of pre-owned devices. This approach ensures that the appliances bought by homeowners will run on the newest, most efficient technologies. Recent findings from regions with stringent energy rating systems also suggest that regulations and programs can lead to a 50% cut in the electricity consumed by appliances. Global initiatives, such as the United for Efficiency (U4E) partnership, which seeks to shift appliance markets in low- and middle-income countries into high-efficiency devices, are increasingly needed for the potential energy savings to be realized as a climate solution.

What is our assessment?

Based on our analysis, using low-flow fixtures is a cost-effective strategy for reducing water consumption, but has only a modest impact on GHG emissions. Therefore, this climate solution is “Worthwhile.”

What is it?

Low-flow fixtures lessen the total consumption of water by reducing flow rates through a household faucet or shower. Less hot water use means fewer emissions from the energy source used to heat the water, and it also means fewer emissions from pumping and treating tap water. Heating water for showers, sinks, and other domestic appliances is often the second largest source of emissions from buildings after space heating. Modern low-flow showerheads can produce comparable pressure and coverage to traditional showerheads through aeration and/or laminar flow. Aerators for faucets and low-flow showerheads are relatively low-cost investments that users can install themselves.

Does it work?

Low-flow fixtures reduce emissions from heating, delivering, and treating water by reducing hot water consumption. There is ample evidence for water savings with low-flow fixtures, as well as for the linkage between quantity and source of energy used for water heating and GHG emissions. Additionally, there is substantial research on the emissions from treating and pumping water, which can be reduced through water conservation. Low-flow fixtures are readily available, and performance labels are available to help consumers select quality products.

Why are we excited?

Low-flow fixtures conserve water, which reduces emissions, reduces energy demand, saves consumers money, and helps with sustainable water resource management. Households that adopt low-flow fixtures can enjoy significant utility bill savings because these fixtures reduce both water consumption and the energy used to heat water in the home. Faucet aerators also produce a smoother water stream with less splashing, and along with low-flow showerheads, are low-cost and simple to install. Household water conservation practices, such as low-flow fixtures, can help with regional sustainable water resource management and defer infrastructure expansion projects. This is particularly important in areas where water resources are increasingly strained due to climate change, growing populations, and other factors. In some regions, community water conservation efforts have had measurable impacts on water treatment costs, resulting in lower water rates for consumers.  

Why are we concerned?

Even with widespread adoption, low-flow fixtures would have a relatively small impact on GHG emissions. Moreover, the low cost and ease of replacement mean that low-flow fixtures can be easily reverted to less efficient fixtures, eliminating the emissions impact and other benefits. Lastly, although modern quality low-flow showerheads are comparable to traditional fixtures, the poor quality of early low-flow showerheads may have contributed to decreasing levels of adoption in some areas.