Geological net zero: what it means, why it matters and who should deliver it?

What is geological net zero?  

You may be familiar with the concept of net zero, which refers to the balancing of greenhouse gas (GHG) emissions with removals. But you may be less familiar with geological net zero. I first encountered this term while watching a Gresham College lecture by Professor Myles Allen, which explored how we can prevent fossil fuels from causing global warming. Geological net zero is a more specific and strict idea. It essentially means that for every tonne of carbon dioxide (CO2) released into the atmosphere derived from fossil fuels (also referred to as fossil carbon), an equivalent tonne is permanently and safely stored underground in the Earth’s subsurface. In other words, it mirrors the logic of net zero, but restricts the types of removals that count – only durable, geological storage qualifies.

What is the carbon cycle?  

To understand the rationale behind geological net zero, it helps to refer to the carbon cycle – the continuous movement of carbon through the biosphere (living organisms), geosphere (solid Earth), hydrosphere (water) and atmosphere (air). Within this system, scientists distinguish between the fast carbon cycle (the biological cycle), and the slow cycle (the geological cycle). As the name suggests, the key difference is the speed at which these cycles operate. Carbon can move through the fast cycle in timescales of years to decades, whereas the slow cycle operates over millions of years.
Human activity is disrupting the natural carbon cycle in several ways, most notably by extracting carbon from the geosphere in the form of fossil fuels and releasing it into the atmosphere through combustion. This continuous transfer of fossil carbon into the atmosphere is creating an imbalance in the carbon cycle. Natural systems are attempting to compensate: oceans and forests are absorbing increasing amounts of CO2, but they are under strain and cannot keep pace with the excess. As a result, global temperatures continue to rise and the oceans are becoming more acidic.

What are biological and geological carbon removal solutions? 

One way to ease pressure on the environment and slow global warming is through interventions that harness biological processes, such as nature-based solutions. This could include reforestation, afforestation and wetland rehabilitation. These interventions actively remove CO2 from the atmosphere and deliver numerous co-benefits – supporting wildlife, preventing soil erosion and lowering flood risk. However, when viewed through the lens of the carbon cycle, these solutions operate within the biological, or fast, carbon cycle. This means they only offer short-term carbon relief, as within tens to hundreds of years, the captured and stored carbon will eventually return to the atmosphere.

If we want to remove carbon from the atmosphere on a longer-term basis, we can look to the geological, or slow, carbon cycle – the part of the system that involves storing carbon in the geosphere. This is where technological CO2 removal comes into the picture, which involves either capturing CO2 directly from the atmosphere or preventing it from entering the atmosphere in the first place, and then storing it safely underground in the Earth’s subsurface. Once stored in geological formations, the carbon can remain isolated for millions of years, providing the kind of durable removal that biological processes cannot offer.

Nature-based solutions play an important role in achieving our environmental goals, but storing carbon at the Earth’s surface leaves it vulnerable to climate change itself and comes with a relatively high risk of reversal – meaning the stored carbon can be released back into the atmosphere through events such as fire, disease and land-use change. Their overall capacity is also limited by land availability, which is already under pressure from competing priorities such as food production and infrastructure development. Forestry Research (no date) in the UK further notes that “even the most ambitious afforestation plans will only be able to offset a small proportion of total current national emissions”.

Nature-based solutions remain essential for near-term mitigation and other environmental services. However, it is clear that we should not rely solely on emission reductions and nature-based solutions to meet our climate goals. This becomes even more important if fossil fuels remain in use for the foreseeable future, a scenario that is widely expected, with some experts anticipating their use well beyond 2100.

How does geological carbon storage work? 

Capture
When discussing technological CO2 removal and storage technologies, carbon capture and storage (CCS) is the overarching term that covers several approaches, including point source carbon capture and storage, bioenergy with carbon capture and storage (BECCS), and direct air capture (DAC). All three rely on geological storage, where CO2 is injected deep underground for long-term containment.
Point source CCS involves capturing carbon directly from industrial exhaust steams before it enters the atmosphere. The CO2 is separated from flue gases, concentrated and compressed before it is transported to a geological storage site, typically via pipelines. BECCS uses the same capture and storage process, but applies it specifically to bioenergy facility’s. CCS can significantly reduce emissions from power plants and industrial processes, but cannot address dispersed emissions from sectors such as aviation. This is where DACs become important, which uses large fans to draw ambient air through a contractor, where the CO2  is separated and compressed before being sent to storage. A big advantage of DACs is that they can be installed next to the storage site, which removes the need for long-distance CO2 transportation.

Storage  
Once the CO2 has been captured, compressed and transported to the storage site, it is injected underground either through converted production wells in former oil and gas reservoirs, or through dedicated wells drilled specifically for carbon storage. The main advantage of using depleted oil and gas reservoirs is that the geology is known and proven to trap hydrocarbons, which reduces time and costs to identify suitable storage sites. After injection, the CO2 either mixes with residual reservoir fluids or occupies the same pore space that previously held hydrocarbons, where it becomes structurally trapped beneath an impermeable caprock. In essence, the process mirrors hydrocarbon production but in reverse.

What are the concerns with technological carbon removals? 

Regarding point-source CCS in particular, many argue that it provides a lifeline for the fossil fuel industry and distracts from more effective decarbonisation strategies. I can see how this concern arises. However, if fossil fuels are expected to remain in use well beyond 2100 anyway, it would make sense to decarbonise them – something that CCS is specifically designed to enable.  Another well documented criticism concerns energy demand. Capturing, compressing, transporting and storing carbon is energy intensive, and if that energy is supplied by fossil sources, technological solutions could inadvertently add to the very problem they aim to solve. A further challenge is cost. Building the capture plants, pipelines and developing storage sites requires substantial upfront investment, even operating, maintaining and monitoring requires continuous expenditure. DACs in particular are thought to be one of the most expensive forms of CO2 removal.. This raises the question of whether or not these technologies can be deployed cheaply and fast enough to make a meaningful contribution to climate goals.

Is there any policy around carbon capture and storage?  

Globally, there is currently no policy that mandates CCS. The main exception is the EU, where the Net Zero Industry Act requires large oil and gas producers to develop 50 million tonnes of CO2 injection capacity per year by 2030. This is a significant step forward, making the development of geological storage a legal obligation – although it does not require companies to actually inject CO2. In contrast, the UK and several other countries support CCS through subsidies or tax credits, but do not require companies to capture or store carbon.

Going back to the Gresham Lecture by Myles Allen, some experts are advocating for a Carbon Take Back Obligation (CTBO). Under this policy, fossil fuel extractors would be required to permanently store an amount of CO2 equivalent to the emissions generated by the products that they sell. The obligation would be progressively scaled, starting with the requirement to store a fraction of associated emissions and rising to 100% by 2050 – meaning one tonne stored for every tonne emitted. This would be a radical policy that puts the responsibility of cleaning up fossil carbon squarely on the companies that produce it, and who have the geological expertise and infrastructure to do so. Importantly, it would also eliminate the need for subsidies and tax credits, removing the burden from taxpayers. As Myles Allen argues, it would be comparable to requiring nuclear power companies to manage and safely store nuclear waste – we don’t simply allow them to discard it anywhere.

As you would imagine, the CTBO also has its critics, and not just from the oil and gas industry. Opponents argue that this policy could undermine efforts to phase out fossil fuels by allowing their continued use. They also highlight that CTBO relies heavily on CCS which remains expensive and unproven at the scale required. Another concern is cost past-through, with any additional financial burden placed on fossil fuel companies being passed directly onto consumers, affecting fuel prices and wider energy costs.

Where does this leave geological net zero? 

The rationale behind geological net zero is clear: the natural carbon cycle cannot keep pace with the amount of fossil carbon we continue to release into the atmosphere, even under deep emission reduction pathways. Geological net zero presents a direct way to restore balance; for every tonne of fossil carbon emitted, an equivalent tonne is permanently returned to the geosphere.

However, geological net zero sits at crossroads: who should be responsible for delivering it? Should the oil and gas producers take responsibility for the carbon embedded in the fuels they sell? These companies have the technical expertise, infrastructure and workforce to develop and operate storage sites. Alternately, does responsibility lie with the organisations who purchase and combust fossil fuels, since they are the ones directly generating emissions? Should taxpayers continue to fund it, or should responsibility be shared across multiple parties? As a society, this is a question we must address to ensure a fair and effective system.

Sources and further reading  

Boot, M., Sundvor., I., Jenkins., S., and Allen., M., 2025. Markets & Mandates: Policy Scenarios for UK CCS Deployment & Exploring the Role of a Carbon Takeback Obligation. Oxford Net Zero, Carbon Balance Initiative, and Carbon Capture and Storage Association. January 2025.
European Commission, no date. The EU’s 2030 carbon storage target. Available online: The EU’s 2030 carbon storage target – Climate Action
Florence School of Regulation, 2025. Carbon Capture and Storage. Available online: Carbon Capture and Storage
Foresty Research, no date. Establishing New Woodland. Available online: Establishing New Woodland – Forest Research
Greenpeace, no date. Carbon capture and storage – what you need to know. Available online: Carbon capture and storage – what you need to know – Greenpeace UK
Gresham College, 2025. Carbon Takeback: How We Will Stop Fossil Fuels from Causing Global Warming. Available online: Carbon Takeback: How We Will Stop Fossil Fuels from Causing Global Warming – Myles Allen
Met Office, no date. Carbon Cycle. Available online: Carbon cycle – Met Office
NASA, 2011. The Carbon Cycle. Available online: The Carbon Cycle – NASA Science
World Resource Institute, 2023. What Exactly are ‘Nature-based Solutions’? Available online: What Exactly Are ‘Nature-Based Solutions’? | World Resources Institute