What is our assessment?

Enhanced geothermal systems (EGS) are emerging as one of the most promising technologies for reliable, utility-scale, zero-carbon energy that can complement wind and solar and strengthen grid resilience. The technology, which is built on an existing base of technical and industrial expertise and capacity, is advancing rapidly through major R&D efforts and early commercial pilots. 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?

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

Does it work?

Electricity production by an enhanced 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 was 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 EGS that use the 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 EGS projects have successfully produced electricity, but no EGS plant has yet achieved full commercial operation at scale. 

Why are we excited?

Enhanced geothermal energy systems are a potentially transformative climate solution for several reasons. First, they could massively expand clean energy availability. EGS 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, including EGS, could supply around 15% of the world’s electricity by 2050. Second, unlike solar and wind energy, enhanced 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. EGS 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, EGS 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 EGS. The application of horizontal 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 EGS. 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 EGS, 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, EGS 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 EGS faster than entirely new industries. 

Why are we concerned?

Despite its promise, EGS 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 enhanced geothermal projects today have high upfront capital costs, primarily due to deep drilling and reservoir stimulation expenses, as well as high operational costs. Current EGS 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. Currently, many EGS use hydraulic fracturing to create the heat exchange reservoirs and circulate fluid underground. In some types of geologies, this 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, EGS could pose risks for groundwater contamination or water consumption in arid regions, although EGS 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 EGS) has received comparatively little support. This means EGS developers may struggle with financing and grid access due to policy gaps or obstacles.  

What is our assessment?

Based on our analysis, Improve Steel Production using H₂-DRI-EAF powered by clean electricity has the potential to significantly reduce emissions. However, while the individual technologies for H₂-DRI-EAF 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). 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. 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. EAF furnaces are already very common in steelmaking and for recycling existing steel, but are rarely combined with H₂-DRI. 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. Finally, technologies to make industrial hydrogen from electricity are mature, 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.  

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. 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%). The impact is potentially significant, given that steelmaking accounted for an estimated 3.7 Gt of CO₂‑eq in 2019. 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. 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. As of 2025, we could find references to only a few pilot facilities producing improved steel as we have defined it here. The entire H₂-DRI-EAF process is considered to be at the large-scale prototype demonstration stage. 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. The higher cost of making low-emission steel is a significant barrier to industrial adoption and consumer demand. Electricity accounts for nearly half the cost of producing low-emission steel from iron ore. 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. 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. Meanwhile, existing steelmaking facilities typically have lifetimes of 25–40 years, which increases the likelihood of stranded assets or continued reliance on fossil fuels by 2050. Under its Sustainable Development Scenario, the International Energy Agency (IEA) projects 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 projections.

What is our assessment?

Based on our assessment, Reduce Airplane Contrails has the potential to rapidly reduce the direct climate warming impact of the aviation industry. However, because the solution is not already being adopted at scale and there is a lack of data on its effectiveness, we will “Keep Watching” this solution.

What is it?

This solution reduces the warming impact of contrails by rerouting airplanes to avoid areas where contrails are likely to form. Contrails (also known as condensation trails) are long, thin clouds that form behind aircraft when the exhaust combines with cold, humid air to produce ice crystals at high altitudes. Contrails can trap heat radiating from the Earth, producing a strong but short-lived warming effect similar to that of greenhouse gases in the atmosphere. Most contrails dissipate quickly (<10 minutes), but under some meteorological conditions, they can persist for many hours. In regions with high air traffic density, contrails can cover a large fraction of the sky area, and even though they may last for only hours, the heat trapped in the atmosphere and oceans by contrails is multiplied by the tens of millions of flights per year. It’s important to note that not all contrails have a warming impact. The degree to which contrails warm or cool the atmosphere varies with time of day, season, atmospheric conditions at cruising altitudes, and whether the clouds form over land or ocean. Contrails that form during the day can have a net cooling effect by reflecting solar radiation back into space. However, the scientific consensus is that contrails overall have a net warming effect.

Does it work?

Modeling studies and field testing suggest that strategically rerouting flights to avoid areas where warming contrails are likely to form can substantially reduce contrail formation and their warming impacts. It is estimated that less than 20% of flights produce persistent contrails with a net warming effect, and rerouting the most impactful of these flights could reduce contrail-induced warming by as much as 80%, providing an immediate climate benefit. Rerouting aircraft to avoid turbulence is already a standard industry practice. These same protocols could be used for contrail avoidance with the addition of model forecasts for contrail formation into pre-flight planning and in-flight sensors and satellite measurements for in-flight responses.  

Why are we excited?

Research suggests that the warming impact of contrails is roughly comparable to and additional to the warming from the direct GHG emissions from the aviation industry’s use of fossil fuels. Strategically rerouting air traffic to reduce the formation of warming contrails could have an immediate and globally meaningful climate impact, making this an “emergency brake” solution with the potential to deliver a beneficial impact more rapidly than many other climate solutions. In addition, this solution could be implemented at scale relatively quickly, even as supportive predictive models, meteorological monitoring, and instrument integration technologies improve. Progress is already being made. Industry trials are already underway, and on-board humidity sensors that can identify when an airplane is moving through a contrail-forming region are being developed. The European Union now requires major aircraft operators to report modeled data on their contrail formation as part of their emissions reporting. This sets the stage for policies that require warming contrail avoidance. Finally, this high-impact climate solution is relatively low-cost. The costs for additional sensors and fuel are estimated to be US$10–15 per flight, or the equivalent of US$1–6/t CO₂‑eq avoided.  

Why are we concerned?

Policy and regulatory changes will be needed to support the adoption of rerouting protocols to avoid warming contrails, and implementation could be restricted by uncertainties in the models and by safety concerns. Multilateral industry and government cooperation will be necessary to draft new regulations to support rerouting to avoid warming contrails, and timelines must be established for mandatory implementation. While models that forecast where warming contrails are likely to form exist, they are limited by a lack of data on humidity levels at cruising altitudes and require more validation to assess how accurately they project contrail formation. In addition, better tools to monitor and model the effectiveness of rerouting in preventing the formation of warming contrails are needed, especially when the added emissions from fuel use could exceed the climate benefits of the contrails avoided. Rerouting opportunities may also be limited by safety concerns in congested airspaces. 

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 chillers for refrigeration. 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. Low-carbon alternatives for district heating can include electric heat pumps, solar thermal, deep geothermal, and even waste heat from other industries. 

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 International Energy Agency (IEA), district heating for all applications accounted for 4% of global emissions in 2022, and roughly 40% of the heat energy from district heating was delivered to industry. China is a major adopter of district heating for industries, with the combustion of coal supplying much of that heat. 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. 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. Some low-carbon options may not be suitable for industrial processes that require higher temperatures than those needed for space heating. 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 (100–200°C) are increasingly available and could become a low-carbon competitor to the use of a conventional district heating system.

What is our assessment?

Based on our analysis, the climate impact of restoring seaweed ecosystems is unclear but likely to be low. While restoration offers important ecological benefits, its effectiveness in removing carbon is understudied, and the implementation costs may be prohibitively high, but require further research. Therefore, we conclude that Restore Seaweed Ecosystems is a solution to “Keep Watching.”

What is it?

Seaweed ecosystem restoration is the deliberate action of reestablishing seaweed in degraded, damaged, or destroyed ecosystems. Seaweed removes CO₂ from seawater through photosynthesis, which allows the ocean to absorb additional CO₂ from the atmosphere. Some of the fixed carbon can be sequestered through export to the deep sea or burial at the seafloor, while a portion may also persist as carbon forms that resist degradation even in the surface ocean. Restoration of seaweed ecosystems helps restore biomass and therefore the productivity of these ecosystems, which can enhance their sequestration capacity. Restoration can occur in a number of ways, but commonly includes transplanting adults, controlling grazers, building artificial reefs, seeding with propagules or spores, remediating pollution, removing competitive species, and culturing. Most restoration efforts have focused on canopy-forming species, such as giant kelp (Macrocystis pyrifera). 

Does it work?

Seaweed ecosystem restoration can be somewhat effective, with nearly 60% of restoration efforts achieving survival rates of over 50%. The first large-scale restoration is thought to have occurred in Japan in the late 1800s. Still, few projects have been implemented at scale, with most restoration efforts below 0.1 ha in size. Moreover, little data exist to evaluate the effectiveness of restored seaweed ecosystems at removing carbon. While theoretically, they should regain functional equivalence to intact systems, this requires further research. The extent of lost and degraded seaweed ecosystems is also poorly understood, making it unclear how restoration efforts might be scaled globally. Additionally, the air-to-sea transfer of CO₂ to replace the CO₂ taken up by photosynthesis in the ocean is not always efficient, meaning removal in the water column may not always translate to equivalent atmospheric CO₂ removal. However, this aspect of effectiveness also remains understudied. Consequently, the climate impact of restoration is uncertain.

Why are we excited?

Healthy seaweed ecosystems provide a range of ecological benefits. Seaweed can help buffer against ocean acidification in some places as functional systems better regulate pH. These systems also provide complex habitats that support a wide range of marine life, such as fish and invertebrates, so restoring seaweed ecosystems can help recover biodiversity. Seaweed ecosystem restoration can also improve nutrient cycling and overall ecosystem resilience to climate stressors.

Why are we concerned?

Restoration of seaweed ecosystems is currently expensive, with costs varying widely depending on the method used. In kelp forests, chemical or manual urchin removal, which reduces grazing pressure, may cost between US$1,700/ha and US$76,000/ha in 2023 dollars, while most other approaches exceed US$590,000/ha.

It’s also unclear whether seaweed restoration efforts could scale enough to have a globally meaningful impact on GHG emissions. Using estimates from intact subtidal brown seaweed ecosystems, which are among the most productive and represent a likely upper limit on the effectiveness of seaweed restoration as a whole, restoration might remove 2.3 tCO₂‑eq /ha/yr. At this rate, over 40 Mha would need to be restored to exceed 0.1 GtCO₂‑eq/yr. However, most restoration projects are under 0.1 ha. For kelp forests, only roughly 2% (19,000 ha) have been restored out of the Kelp Forest Challenge’s target of 1 million ha by 2040, suggesting that this practice may not be scalable currently.

The effectiveness of restoration can also be offset by the life-cycle emissions of products required to re-establish some seaweed ecosystems. For example, emissions from the production of cement blocks needed to afforest some seaweed habitats have been estimated to potentially delay carbon removal benefits for 5–13 years in some systems.