What is our assessment?

Based on the potential for harmful impacts, the risks of using AOE to destroy atmospheric methane outweigh its uncertain benefits. Because of this, as well as the fact that there are other effective solutions to reduce methane emissions already available, this climate solution is Not Recommended.

What is it?

AOE of methane is a technology designed to accelerate the natural decay of methane to CO₂  by increasing the concentration of hydroxyl and chlorine radicals in the air. In the presence of sunlight and oxygen, these molecules convert methane to CO₂. This solution aims to increase the atmospheric concentration of these molecules by injecting precursors, such as iron salts and hydrogen peroxide, into the air.

Does it work?

Methane is a potent greenhouse gas, more than 80 times stronger than CO₂ at trapping heat on a 20-year basis. Under natural conditions, it persists in the atmosphere for about 10 years before it converts into CO₂. Therefore, artificially accelerating methane conversion reduces its disproportionate warming impact. 

There is evidence that the concentration of hydroxyl radicals affects the rate at which methane is converted into CO₂ in the atmosphere. However, research into AOE for methane removal is still in its early stages and limited to a few modeling and laboratory studies. There are currently no real-world examples of atmospheric methane removal. The effectiveness of the solution is unknown and uncertain. Based on current research, no one knows if it is possible to remove atmospheric methane at a meaningful scale in a safe and cost-effective manner. 

Why are we excited?

Because methane is such a potent greenhouse gas, any actions to reduce its concentration in the atmosphere would be emergency brake solutions with immediate and disproportionate climate benefits. In addition, unlike direct air capture or carbon capture and storage, there is no need to capture or store the gas that the process produces. 

Why are we concerned?

AOE for methane removal is an untested technology designed to alter atmospheric chemistry that presents novel and potentially uncontrollable risks to Earth systems and ecosystem processes. Hydroxyl and chlorine radicals are highly reactive molecules, and they do not react solely with methane. When they react with other atmospheric constituents they can generate other, even stronger, climate pollutants such as nitrous oxide as well as other air pollutants such as PM2.5, carbon monoxide, nitrogen dioxide, and ground-level ozone, and they could deplete stratospheric ozone. Some proposed AOE methods, such as atmospheric injection of iron salt aerosols, create chlorine radicals. The chlorine- and iron-containing byproducts of these aerosols could adversely affect ocean chemistry and food webs when they are deposited on the ocean surface (see Deploy Ocean Fertilization). 

Other serious concerns include technical feasibility, scalability, cost, monitoring, reporting and verification, and governance. For example, in order for methane in the atmosphere to be reduced at climate-relevant scales, the production of chlorine or hydroxyl radicals would need to be magnitudes greater than the current global production. Costs have not been estimated, but they would likely be high. New tools for monitoring atmospheric methane would need to be developed to quantify the amounts of methane removed for accurate accounting and verification. Similar to stratospheric aerosol injection, deployment of atmospheric methane removal could pose geopolitical, legal, and ethical challenges. In addition, it could distract from or delay action on other methane reduction approaches, such as managing oil and gas methane, managing coal mine methane, improving landfill management, and increasing centralized composting.

What is our assessment?

Nitrous oxide removal technology is at a very early stage of development. Other available technologies and practices can effectively reduce nitrous oxide emissions. However, because this solution aims to remove such a potent GHG from the atmosphere, we will Keep Watching it. 

What is it?

Nitrous oxide removal is a technology that uses photocatalytic chemicals to convert nitrous oxide, a GHG that has 270 times more warming potential than CO₂ and persists in the atmosphere for more than 100 years, into gaseous nitrogen and oxygen. 

Nitrous oxide is found naturally in the atmosphere, but 40% of emissions come from human activities, and human-caused emissions have increased more than 30% during the past four decades. Most anthropogenic contributions are from fertilizers applied to croplands and other farming activities, while the rest are from fossil fuel use, industrial activities, and waste and wastewater. 

This solution involves spraying a chemical photocatalyst onto agricultural fields. When the photocatalyst is exposed to sunlight and nitrous oxide, it drives a chemical reaction that decomposes nitrous oxide into gaseous nitrogen and oxygen. 

Does it work?

Research into atmospheric nitrous oxide removal is still in its early stages. The concentration of nitrous oxide in the atmosphere is very low, so nitrous oxide removal would likely be implemented in agricultural areas where fertilizer use locally elevates atmospheric concentrations. Laboratory testing has shown that nitrous oxide can be converted into nitrogen and oxygen using light energy and photocatalysts. However, the effectiveness of the solution in practice is uncertain because few experiments have been conducted in real-world settings. The single field study that applied titanium dioxide to a field crop did report a measurable reduction in nitrous oxide emissions. However, there is no evidence that this technology can remove atmospheric nitrous oxide at a meaningful scale. 

Why are we excited?

Because nitrous oxide is such a potent GHG, reducing its concentration in the atmosphere could have a disproportionately beneficial climate impact. In addition, unlike direct air capture or carbon capture and storage, there is no need to capture or store any gases because the nitrous oxide breaks down into gases that have no climate impact. Also, titanium dioxide application to crops is being researched as a method for improving crop resilience.

Why are we concerned?

Serious concerns include technical feasibility, environmental risk (including environmental and food safety), scalability, cost, and monitoring, reporting, and verification. While there is currently very little research on the real-world use of photocatalysts to destroy atmospheric nitrous oxide, ongoing research on the application of nanoparticles of titanium dioxide to crops to enhance productivity and resilience to stress suggests that high concentrations of titanium dioxide can have adverse effects. Furthermore, these nanoparticles are not approved for direct food consumption, and their fate and environmental impacts are poorly understood. 

Tools, methods, and standards need to be developed to quantify nitrous oxide removal for accurate accounting and verification. Costs are unknown. Finally, numerous other approaches for reducing human-caused nitrous oxide emissions exist, including improving nutrient management, rice production, manure management, and industrial processes, as well as reducing fossil-fuel use for power generation and transportation and increasing use of centralized composting. 

What is our assessment?

Based on the difficulty of capturing low concentrations of CO₂ from the air and the associated technological, energy consumption, and financial challenges facing DAC, it is unlikely that this climate technology can be scaled up to remove globally meaningful amounts of CO₂. Furthermore, based on the current financial and policy support for DAC from fossil-fuel interests, there is a clear risk that the technology will be used to enable and perpetuate the production and use of fossil fuels, which is antithetical to solving the climate crisis. Therefore, we conclude that deployment of DAC is “Not Recommended” as a climate solution.

What is it? 

DAC is a suite of engineered technologies that remove CO₂ directly from the atmosphere, concentrate it, and then inject it underground for permanent storage. CO₂ is captured from the atmosphere by moving large volumes of air, usually with large fans, past a reactive material that selectively binds CO₂, either a solid sorbent (referred to as solid-DAC or S-DAC) or a liquid solvent (referred to as liquid-DAC or L-DAC). The captured CO₂ is recovered from the reactive material by applying heat, pressure, or chemical reactions, and collected and compressed for transportation and storage. The concentrated CO₂ is then injected deep underground into geological formations, such as saline aquifers or basalt formations, where it can be permanently stored. 

Does it work?

The technology and chemistry for the selective capture of CO₂ from air are effective, although the CO₂ capture efficiency varies with the reactive material and other factors. A variety of solid and liquid reactive materials have been developed, along with material-specific processes for recovering captured CO₂ and regenerating the sorbents. This process is very energy-intensive and, for liquid-DAC, water-intensive. To capture and recover 1 t CO₂, solid-DAC uses about 1,100 kWh, while liquid-DAC uses about 2,500 kWh and consumes as much as 7 t of water. Most of the energy for DAC (70–90%) is used to generate heat for recovery of the captured CO₂ and regeneration of the sorbent material. Liquid-DAC requires temperatures up to about 900 °C (1,652 °F), while solid-DAC requires temperatures of only about 100 °C (212 °F). Because the process is so energy intensive, DAC achieves net carbon removal – capturing and sequestering more CO₂ than it emits – only if it is powered by zero or low-carbon energy sources and/or uses waste heat. For example, recent reporting showed that the amount of CO₂ captured and stored by Climeworks, the largest commercial DAC company currently in operation, was insufficient to offset the facility’s operational GHG emissions. CO₂ captured by a DAC facility can also be used for other purposes, such as enhanced oil recovery or production of algae biofuels. However, life cycle analyses conducted by the National Energy Technology Laboratory show that these pathways do not result in net carbon removal due to the emissions from production and/or use of these other products. Therefore, in addition to its requirements for zero or low-carbon energy, DAC can only be an effective method for net carbon removal if the CO₂ it captures is permanently stored deep underground. With appropriate pre-injection site selection, geologic testing, and post-injection monitoring, underground storage of CO₂ is safe and effectively permanent.

Why are we excited about it?

Unlike some other carbon removal technologies and practices, a DAC facility has a relatively small footprint and can be located anywhere there is sufficient low-carbon energy and infrastructure and capacity to transport or store captured CO₂. In addition, the amount of CO₂ removed from the atmosphere can be directly measured by monitoring the flow and concentration of captured CO₂ at the point of storage. Compared to many other carbon removal approaches, this method provides a higher level of confidence in the amount of CO₂ being removed for investors and carbon credit purchasers. The geological sequestration of captured CO₂ has high permanence, effectively removing CO₂ from the atmosphere for thousands of years with a low risk of reversal. There are numerous research and pilot projects underway to improve CO₂ capture efficiency, reduce energy use, and reduce costs, which may improve the effectiveness and cost of this technology. 

Why are we concerned?

The concentration of CO₂ in the atmosphere is small, currently about 420 parts per million, or about 0.04%. This means that a DAC facility must process huge amounts of air – more than 1,600 t by one estimate – and consume more energy than a typical U.S. household uses in a month to capture 1 t CO₂. Scaled up to remove a globally meaningful amount of CO₂ (>0.1 Gt CO₂ /yr), DAC would consume more energy than the annual energy consumption of 10 million U.S. households. In addition, removing and storing CO₂ using DAC is very expensive, costing up to US$1,000/t CO₂ stored. This is more than twice the cost per t for all other commercially available carbon removal technologies and practices. 

For these reasons, the technical and financial feasibility of scaling DAC to remove globally meaningful amounts of CO₂ from the atmosphere is low. Despite these challenges, as of September 2025, more than 30 companies have sold more than 2.4 million t of future carbon removal credits. However, less than 1,300 t CO₂ has actually been removed so far – or only 0.05% of these promised credits. To put this in perspective, despite spending billions of dollars, DAC has removed about as much CO₂ as would be saved by keeping 250-300 cars off the road for a single year.

There is also an opportunity cost for DAC. Even if a DAC facility is powered by solar, wind, geothermal, or nuclear energy, that carbon-free energy could have been used to displace coal- and gas-powered electricity instead, reducing emissions by far more than a DAC facility can capture and store. Similarly, the large amounts of public and private sector funding going to DAC could be more cost-effective and carbon-effective if used for other, more effective actions to cut emissions or remove CO₂. There is also the risk that DAC will be used to delay or avoid emissions reduction actions or for greenwashing by fossil fuel companies and other emitters. Substantial amounts of the funding supporting the development of DAC are coming from fossil fuel companies, which have publicly stated that they view carbon capture as a strategy to extend society’s use of fossil fuels. Finally, unlike most other emissions reduction or carbon removal actions, DAC provides no obvious other benefits to nature or human well-being.