Key points 

  • To achieve our climate goals, total global fossil fuel demand needs to fall substantially, even in a scenario where 'abated' fossil fuels are permitted. 
  • Fitting Carbon Capture and Storage technology to fossil fuel plants does not automatically mean that carbon dioxide emissions have been 'abated' in line with the Paris Agreement goals. Without a formally agreed definition of what is meant by 'abatement', there is a risk that these goals will be compromised. 
  • To qualify as 'abated', fossil fuel plants must achieve: near total containment of methane emissions associated with extraction, processing and transport; near total containment of end-use combustion carbon dioxide emissions both for fuel production and use; and permanent storage of the captured carbon dioxide.  
  • The term 'abated' should be reserved for where the ongoing emissions from using fossil fuels are reduced 90-95% or more; upstream fugitive methane emissions are less than 0.5%, and approaching 0.2%, of equivalent natural gas production; and captured emissions are stored permanently. 

Why does the definition of 'abated' matter?

In the run up to COP28, several influential stakeholders—including the G7 and European Council—have called for the phase out of 'unabated fossil fuel'. This is different to calling for the phase out of fossil fuels (which refers to phasing out all fossil fuels) because it would permit some continued usage of fossil fuels, so long as they were 'abated'.

The issue, however, is that while 'abated' is generally understood to mean that some form of Carbon Capture and Storage (CCS) technology would be used to capture the emissions resulting from the use of fossil fuels, there is currently no formally agreed definition of the standard to which this would be expected to operate.  

It might seem reasonable to assume that 'abated' fossil fuels would have no, or very minimal, levels of associated greenhouse gas emissions. But in fact, fitting CCS technology does not automatically achieve this. If the definition of 'abated' is left open to interpretation, there is a risk that it could inadvertently allow the continued emission of greenhouse gases. This might happen in several ways: 

  1. Upstream 'fugitive' emissions of methane associated with the extraction of fossil fuels may continue. According to the IPCC, emissions of methane that occur during the production and transport of fossil fuels currently account for around 18% of global greenhouse gas emissions from energy supply, and there is recent evidence and an accumulating literature that this is underestimated by at least 50-100%. 
  2. Facilities that capture only a proportion of emissions may be permitted. For example, plants that captured, say, only 50-60%, rather than 90-95% or more of emissions could be allowed to continue to run.  Some CCS applications—such as Steam Methane Reforming (SMR) units used to make hydrogen from natural gas—typically have capture rates in the 50-60% range, compared to their close cousins, Autothermal Reformers (aka ATR), which allow relatively cheap 95%+ capture rates.  
  3. Carbon usage or storage mechanisms that are not permanent might be permitted. Geological storage is thought to last for ten thousand years or longer but where the carbon that is captured is used in products, the storage timescales are shorter. Usage in cement and aggregates is considered to sequester carbon for centuries, plastics for decades while use in fuels stores carbon for only a few days or months. 

How should 'abated' be defined?

The authors argue that to qualify as 'abated', fossil fuel plants must meet three criteria: 

  1. There must be near total containment of methane emissions associated with extraction, processing and transport of fossil fuels.  
  2. There must be near total containment of fuel production and end-use combustion carbon dioxide emissions. 
  3. There must be permanent storage of the carbon dioxide. 

They suggest the following definition as one that would be compliant with the Paris Agreement goals: 

The term 'abated' should be reserved for where ongoing fossil fuel use emissions are reduced 90-95% or more; upstream fugitives are less than 0.5%, and towards 0.2%, of equivalent natural gas production; and captured emissions are stored permanently. 

It goes without saying that facilities that do not comply with these criteria would therefore be considered as 'unabated'. 

Do we still need to reduce fossil fuel use?

It is important to note that fossil fuel abatement is not a get out of jail free card. The IEA’s Net Zero Energy Scenario sees significant cuts in demand for all total fossil fuel demand between 2022 and 2050: 

  • oil supply falls by 78%; 
  • gas supply falls by 78%; 
  • coal supply falls by 92%; and 
  • total fossil fuel supply falls by 83%.

This is necessary because delivering CCS facilities at scale is challenging for both technical and economic reasons.   

From a technical point of view, the criteria set out in our proposed definition will not be easy to meet in the short term, but they are technically feasible: 

  • Capturing more than 90-95% emissions has been achieved, but only in projects with concentrated carbon dioxide flows (such as enhanced oil & gas recovery using carbon dioxide). It has not yet been broadly commercially achieved in post-combustion CCS, where there are other gases and particulate matter mixed in with the carbon dioxide.
  • Fossil fuel production practices in Norway, the Netherlands and the UK ensure fugitive methane levels of less than 0.5%, but this is not common practice. 

The IEA’s latest assessment concluded that the current deployment rate of CCS is not on track to deliver its Net Zero Emissions by 2050 Scenario; even if all of the projects that are currently in development are delivered, this would still be “substantially below (around a third)” the required level in 2030. 

There is a further question as to whether this is economically feasible; the costs of near total carbon capture may be unattractive compared with the cost of alternative fuels and direct electrification (where this is possible). For example, the cost of building a coal- or gas-fired electricity plant with CCS is almost double what it would be without (although new technologies are likely to bring costs down in future). The cost of CCS varies depending on the source of the carbon dioxide being captured. Industrial processes that produce concentrated carbon dioxide flows will be cheaper than those with more dilute concentrations. Most expensive is capturing carbon dioxide directly from the air.  

Authors and contacts 

This background briefing was written by:

  • Dr Alaa Al Khourdajie, Chemical Engineering Department, Imperial College London 
  • Dr Chris Bataille, Columbia University,  Center on Global Energy Policy (CGEP) & Institut du Développement Durable et des Relations Internationales (  
  • Jenny Bird, Campaign Manager, Grantham Institute, Imperial College London 

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Further reading 


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