Prof Gibbins NETS0044

Written evidence submitted by Professor Jon Gibbins

Personal evidence from Jon Gibbins, Professor of CCS, University of Sheffield and Director, UK CCS Research Centre.

1Summary of main points being made in this evidence:

  1. The climate science is what matters – avoiding dangerous climate change is very likely to require global net negative CO2 emissions, not just net zero, so the sooner people are able to, and eventually have to, pay for NETs the better.
  2. Engineered NETs are likely to be available at any required scale and, where the polluter pays, should be regarded as just another way of reducing CO2 emissions to the atmosphere.
  3. DACCS, the NET least constrained by nature, has fundamental energy requirements that are of the order of only twice that of point source capture and can take place anywhere and be run 24/7; a range of technology options are available.
  4. Engineered NETs, particularly DACCS, development has been blighted by it being incorrectly classified as geoengineering and lack of government funding for independent scientific research and analysis.
  5. DACCS and BECCS development in the UK can be every rapid once CCUS infrastructure is in place – but this process can be helped.

2.  Responses to EAC questions:

2.1               What contribution could NETs (through DACCS, BECCS, and/or other NETs) make to achieving net zero by 2050?

The target is not net zero per se but avoiding dangerous climate change; NETs are now required to make a major contribution to this according to IPCC assessments

2.2               Which ‘hard to decarbonise’ sectors could benefit most from NETs, and which should be prioritised?

NETs can be applied to every sector to reduce CO2 emissions.  Wherever people want to use them, because they offer lower costs or better results, this should be encouraged because it will bring costs down, in particular for the future global net negative emissions phase where the polluter won’t be paying.

2.3               At what technological stage are current NETs, and what is the likely timeframe that will allow NETs to be operational at scale in the UK?

Combustion-based BECCS is sufficiently proven for large-scale (multi MtCO2/yr) deployment with due attention to first-of-a-kind risks, gasification-based BECCS needs to be proven feasible; DACCS is ready to be trialled at a range of scales but is almost entirely unproven.  

2.4               What are, and have been, the barriers to further development of NETs? How can such barriers be overcome?

Lack of access to CO2 transport and storage has been a barrier but UK infrastructure is coming. Prejudice against NETs has handicapped development of the underpinning science and funding mechanisms, improvement needs government funding and time.  If rational use of NETs is sanctioned and supported then a market is likely to develop.

2.5               What, if any, are the links and co-benefits to other technological innovations, such as sustainable aviation fuel or sustainability in the energy sector?

Capturing CO2 from the air is the key to avoiding emissions from many applications.  Whether the captured CO2 is then better permanently stored (i.e. NET) or (mostly – some will need to be stored to give net zero) reacted with electrolytic H2 depends on relative costs – the climate effects are exactly equivalent.

2.6               What are the trade-offs between availability of land and availability of sustainable biomass to make NETs a viable option in and beyond the UK?

This question seems to be based on incorrect assumptions.  Available biomass (including wastes) should generally be used with CCS, but is a limited resource. DACCS can be powered by fossil fuels if required and be done anywhere in the world so, effectively, is not limited by the availability of renewable energy or land.

2.7               What are the options for the storage of captured carbon, whether onshore or offshore?

The only large-scale option for the UK (and most other places) that need be considered at the moment is geological storage, in the UK all offshore.  CO2 can be held securely in carbonates, principally calcium carbonates, but the lime used to trap the CO2 needs to be made with CCS using geological storage.

2.8               What other drawbacks for the environment and society would need to be overcome to make NETs operational?

NETs cost more money than just dumping fossil CO2 into the atmosphere for free – so does paying for a proper sewage system instead of throwing it in the street or the nearest water course.  They are both necessary costs to maintain a civilised society – we are just a bit later in developing NETs – so society will have to get used to it or take the consequences.  Fortunately emitting fossil CO2 to the atmosphere is more optional than sewage production so people can choose alternatives, or just doing without, in many cases.

2.9               Given the proposed role of NETs in climate change modelling, is there a danger of over-reliance on these technologies in net zero strategies?

The objective is to avoid dangerous climate change and just achieving net zero is now unlikely to do this – the climate science indicates that extended periods of global net-negative emissions are likely to be required.

2.10              How should the UK Government support the further development of NETs?

a) Make CO2 T&S available;

b) be consistent and allow unrestricted use of NETs for emissions reduction;

c) see that all aspects of NETs science are properly supported;

d) moderately support the nascent DACCS industry; and

e) get as much UK biomass and biogenic wastes used with CCS as reasonably possible.

See also 2.4 above.

2.11               What policy changes, if any, are needed to ensure the UK gains a competitive advantage and remains at the cutting edge of this sector?

Consistent treatment of NETs for delivering CO2 emissions reduction, with no restrictions on their use if they are properly conducted.

2.12              The Government has indicated it will publish a Biomass Strategy in 2022, including the role of BECCS. What should be included in this strategy?

Separate valuation of net atmospheric CO2 capture from biomass used with CCS, as distinct from the value (possibly time-dependent) of the energy it can produceRealistic measures to address the fact that biomass gasification, especially for syngas for H2 production etc. is currently unproven and may be intrinsically infeasible, and that this infeasibly, being a negative, is unprovable. Reasonable maximisation of UK’s biomass recovery as part of waste and land amenity management strategies.


3. Supporting information

3.1                The climate science is what matters – avoiding dangerous climate change is very likely to require global net negative CO2 emissions, not just net zero, so the sooner people are able to, and eventually have to, pay for NETs the better

3.1.1               The evidence from the Intergovernmental Panel on Climate Change (IPCC) summarised in the figures below is clear; just achieving global ‘net zero’ rapidly is very likely not enough to avoid levels of climate change that are likely to be dangerous. Given GHG emission history, current trends, and almost any likely GHG emission reduction scenario and climate response, an extended period of global net negative emissions is very likely to be needed to ensure a global temperature rise of less than two degrees.

3.1.2               So just achieving net zero by 2050 is not a sufficient objective; a steep downwards trajectory in 2050, rather than the often-assumed asymptotic approach to net zero GHG emissions, is also required.  The energy/climate infrastructure in 2050 therefore needs to include very significant amounts of NETs so that this sector can be expanded further at a practicable rate to give the overall net negative emissions that are likely to be required.

3.1.3              Immediate rapid development and deployment of NETs, in particular DACCS technologies that can be scaled up to large total tonnages, is an effective way to alleviate the burden that large amounts of CO2 removal from the atmosphere will place on future generations.  This will ensure that fully-developed technologies are available at as low a cost as possible.  Early availability of NETs will also allow people or organisations to choose to use them to remove more CO2 from that atmosphere than is required to compensate for their own emissions if they wish.


Figure 3.1.1 IPCC model pathways that limit global warming to 1.5°C with no or limited overshoot.

IPCC Special report on global warming of 1.5°C, October 2018 (

Figure 3.1.2 Example pathways from IPCC Working Group I - Climate Change 2021: The Physical Science Basis.


3.2               Engineered NETs are likely to be available at the required scale – the key things is who pays and the sooner people are able to, and eventually have to, pay for NETs the better

3.2.1 Disaggregation of NETs components

This evidence will discuss engineered NETs that involve producing molecular CO2 at some point and storing it permanently; nature based NETs and other engineered NETs options e.g. accelerated rock weathering will not be discussed.

NETs, or even BECCS and DACCS, need to be discussed in terms of their sub-components or sub-processes, which for the bulk of practicable engineered NETs in the UK can be characterised as:

a)               CO2 removal from the atmosphere (CDR) and

b)              transport and secure geological storage for the captured CO2 (CO2 T&S).

The main CDR options are:

a1)              direct air capture of CO2 (DAC), or;

a2)               capture of CO2 from something that has taken CO2 from the air (e.g. biomass, limestone from lime), or;

a3)               capture of CO2 from something that will subsequently take CO2 from the air (e.g. limestone, as lime, concrete) and can potentially then retain that CO2 (as carbonate) indefinitely (i.e. conventional concrete made with CCS is a way to do DACCS).

CDR can be used with CO2 storage for negative emissions, but also as a source for (potentially) climate-neutral CO2 to be used to make or do something.  In this latter case some of the CO2 may also be more-or-less permanently stored, but amounts are expected to be relatively small and these applications will not be discussed further.  The main use expected for CO2 captured from air is to make fuels (i.e. sustainable aviation fuels etc.) containing carbon that can then legitimately be released back into the air.  The climate benefits of:

i) CDR + fuel synthesis; or

ii) CDR + T&S for indirect CCS on fossil fuel use

are identical (see Figure 3.2.1) and there should be no artificial discrimination between them.

An illustration of the scope for an engineered CCUS ‘ecosystem’, with DAC and biomass plus capture as well as CO2 T&S and CO2 conversion to fuels etc., is shown in Figure 3.2.2.

The necessary UK CO2 transport and storage infrastructure for engineered NETs is being developed as described in the Net Zero Strategy.  This commits to deploying a minimum of two CCUS clusters by the mid-2020s, and four by 2030, with infrastructure to capture and store a UK total of 20-30 MtCO2 per year by 2030. The first two of these clusters, Hynet and East Coast, have recently been announced and the other two cannot be very far behind to meet the stated timeline.  UK geological storage capacity is expected to be well in excess of foreseeable national requirements.  Additional information is available on the UKCCSRC website[1].  The atmosphere is well-mixed and CDR with CO2 storage can be undertaken anywhere in the world. At a global scale significant amounts of geological storage are also expected to be available (see Figure 3.2.3), with total amounts estimated to be in excess of fossil fuel reserves[2].













Figure 3.2.1 Net zero hydrocarbons (beyond biomass limitations) have CDR at the centre

Costs for green H2 vs. fossil fuel production and CO2 storage determine relative costs of net zero HC options; utility and price of DAC plus other costs vs. utility and price for other energy vectors determines total market size.

Figure 3.2.2 A CCUS ‘ecosystem’ that includes CDR (light blue lines/boxes - mainly DAC and biomass with capture) and CO2 T&S

Figure 3.2.3 Storage prospectivity of CO2 for the world's sedimentary basins


3.3                DACCS, the NET least constrained by nature, has fundamental energy requirements that are of the order of only twice that of point source capture and can take place anywhere and be run 24/7; a range of technology options are available

DAC is not as fundamentally difficult as it might seem.  Fig. 3.3.1 shows that the theoretical thermodynamic minimum energy for separating CO2 from the air is only about twice the energy for capturing CO2 from a gas turbine flue gas and, given that the subsequent compression for T&S (typically to 100-150 atmospheres) is the same for both processes, the overall energy requirements are even closer.

Given the competing commercial claims and lack of transparent information on proposed DAC technologies and projects these will not be discussed in detail.  DAC technologies at the moment appear generally to fall in two areas:

a)    absorption or adsorption of air CO2 using liquids or solids with the CO2 released by low-temperature heating (<200oC) or other mild intervention

b)   reaction with lime, possibly with an intermediate alkaline solution, to form calcium carbonate, from which the CO2 can be released at high temperatures (>800oC)

The choice of basic approach then determines air contactor geometry and passive/active operation, scaling opportunities (i.e. multiple smaller units or larger single units) and integration with the required energy sources (i.e. ‘waste’ low- or high-grade heat, electricity, fossil fuel etc.).

It seems likely that DAC will follow a similar pattern to other new industries e.g. motor vehicles.  A few initial examples will expand to a very wide range of different suppliers and models, then contract to a limited number of proven options, with characteristics that suit a particular user’s requirements.

The Climate Change Committee has assumed DACCS costs of £180-300/tCO2 captured and stored by 2050[3].  This may seem high, but needs to be contrasted with other options, particularly for mobile, small or intermittent sources.  For example, ‘blue’ hydrogen made from natural gas replacing unabated natural gas use is predicted to cost £130-200/tCO2 avoided in 2050 just to produce the hydrogen (see Annex 1); the additional costs for H2 distribution, possibly storage, equipment upgrading etc. must be added to this.  This may make BECCS, or even DACCS, a preferable abatement option for applications such as hybrid gas/heat pump heating or for cooking.














Figure 3.3.1 Theoretical energy input for CO2 capture as a function of CO2 concentration[4]

3.4               Engineered NETs, particularly DACCS, development has been blighted by it being incorrectly classified as geoengineering and lack of government funding for independent scientific research and analysis

DAC is still suffering badly from previous neglect.  For a long time it was seen, at best, as a distraction from capture on CO2 point sources or, worse, as being dangerous ‘geoengineering’

How taking, effectively, fossil carbon, that shouldn’t be there, out of the atmosphere was not rather qualified as entirely the opposite of geoengineering (geo-restoration perhaps?) cannot be explained.

In 2015, however, the US National Academies published a landmark report[5] on NETs, clearly differentiated from a partner report on Solar Radiation Management[6] – it might well be said that this was the time that DAC, and CDR generally, finally came out from under a cloud! 

Six years is not long enough, however, for DAC to have had proper scientific attention.  And academic research funding for DAC has still been hard to obtain.  The flagship RCUK GGR programme run by NERC from 2017 did not fund any DAC grants out of £9M funding[7] and the 2021 UKRI/BBSRC £30M GGR Programme[8] did not fund a DAC or BECCS project either.  Government funding for industrial DAC development has also been limited until recently.  The relatively limited number of longer term pilot-scale DAC examples (e.g. Carbon Engineering, Climeworks, Global Thermostat) appear to have been established with mainly non-governmental funding.

As a result of this lack of funding and perceived ‘career limiting’ or ‘crank’ status the independent, public-domain scientific body of knowledge on DAC is limited.  At the same time, a rapid growth in commercial, and government, interest in pilot- and demo-scale DAC development has led to greater commercial secrecy and competiveness in that community than hitherto.  Things will no doubt have become somewhat clearer after perhaps 5 years, by when a number of the proposed commercial DAC developers will have had an opportunity to be adequately tested.  Unless additional government funds are devoted to open-access scientific work, however, reliable public-domain information and analysis may still be scarce.


3.5              DACCS and BECCS development in the UK can be every rapid once CCUS infrastructure is in place – but this process can be helped

Some suggestions are:

a)         Treat engineered CDR + T&S to permanent geological storage as what it is, indirect capture of anthropogenic CO2 emissions that can be applied for any emission reduction purpose in any quantity, so long as the polluter pays.

b)        Require access under reasonable terms to government supported CO2 T&S for the many smaller CDR projects that are being developed.

c)         Support independent academic research and analysis on CDR, especially DAC, which can be objective because it is not tied to technology development.

d)        Provide some direct government support for DACCS, but be aware that field is very immature and many additional options are likely to become available.

e)         Link most future use of biomass to CCS – the current permitting system allows 299MW biomass plants that are not even capture ready.

f)          Value the NETs potential for UK waste streams when considering processing them, e.g. BECCS may be preferable to composting.

Annex 1: Abatement costs calculated from BEIS predictions for 2050 H2 production from natural gas

Calculated results, assuming 1 MWh (HHV or LHV) H2 can be used to replace 1 MWh (HHV or LHV) of natural gas, are shown in red. BEIS spreadsheet data apart from: Assumed specific CO2 emissions for natural gas = 184 kgCO2/MWh HHV; Natural gas HHV/LHV = 1.109; Hydrogen HHV/LHV = 1.183.

October 2021




[4] Jon Gibbins, Alternative NETs to BECCS: Direct Air Capture, Our Common Future Under Climate Change, Paris. Conference Session 3307: 9 July 2015