The solution space discussed at COP26 is unrealisable: comparing supply and demand for the three zero-emissions resources

Julian Allwood – 16th November 2021

Read the related article in the Financial Times


If incumbent governments and incumbent high-emitting businesses are the main players in defining pathways to reach zero emissions, they will only consider mitigation options that are direct substitutes for the activities that cause emissions today. Their goal is that mitigation should be delivered in such a way that voters/consumers don’t notice. Thus: fossil-aviation will be replaced with “jet-zero” aviation; blast-furnace steel will be replaced with hydrogen-steel; ruminant emissions, which cannot be avoided, must be countered with “negative emissions technologies.” The political discussions at COP26 only considered solutions of this form.

If today’s emitting activities are to be replaced by non-emitting direct equivalents, we have only three resources to draw-on: non-emitting electricity (produced by renewables, hydro-power or nuclear fission) – we’ll call this nelectricity to save words; carbon capture and storage (CCS) to take pure carbon dioxide, compress it, and pump it 2-3km underground for long-term storage porous rocks; biomass. Every technological equivalent to today’s emitting activities requires one or more of these three resources.

Hydrogen does not exist in native form – it must be made either with CCS or by nelectricity. Negative emissions technologies such as direct air capture must be powered by nelectricity and connected to CCS. (Afforestation has only a slow and relatively small negative emissions benefit). All options for “jet zero” depend on nelectricity or biomass.

As incumbent governments and the incumbent high-emitting sectors proclaim their commitment to “net zero” we therefore need to ask a very simple question of accounting: how does their anticipated demand for nelectricity, CCS and biomass compare with likely supply? 


We don’t know how demand for steel, flying or meat will grow, so we’ll compare the resources required to replace today’s emitting activities with today’s supply of the three key resources. Then we’ll look at likely growth rates.

Anticipated demand for nelectricity, CCS and biomass

The table below lists the main sources of global emissions today, translates them into physical units, and reveals the resources required by the main options discussed at COP26 for replacing them. The data used to populate this table is discussed below, and I would welcome any suggestions for additional credible data.

Table 1: The main technical options for mitigation discussed at COP26

Anticipated supply of nelectricity, CCS and biomass

The history of global non-emitting electricity generation is shown in figure 1.

Figure 1: Global generation of electricity without emissions since 1965 (Data from BP Statistical Review of World Energy, 2021)

Since 2010, this generation has been growing at a rate of 350TWh/yr/yr.

The history of global CCS capacity is shown in figure 2. Note that this is capacity, not actual capture – as the industry does not reveal what fraction of capacity is actually used. Almost all of the capacity is currently used for Enhanced Oil Recovery – extracting more fossil fuel from the ground which leads to an increase in emissions.

Figure 2: Global deployment of CCS (data from the oil and gas funded Global CCS Institute – the main lobby for CCS deployment.)

CCS does not work perfectly – estimates of how much of the input stream of carbon dioxide gas is actually captured range from 85-95% – the rest is still released to the atmosphere. The figure reveals that current capacity is nearly 40 Mt/yr of carbon dioxide capture and storage, and over the past decade this grown at an average rate of 1Mt/yr/yr.

A snapshot of current global land-use and harvest is shown in figure 3. This is rather a busy figure, using Sankey diagrams in which the width of each line is proportional to land area on the left and Carbon (the main component of dry biomass) on the right.

Figure 3: Global land-use and biomass harvest (Bajzelj et al. 2014)

The key information to take from figure 3, from the top-right most line, is that the total food harvest of all global agriculture adds up to 100kg of dry biomass (carbon) per person (i.e. 0.7Gt in total.)

In order to estimate future supply of nelectricity, CCS and biomass, we must make assumptions about how supply will expand. The incumbent high-emitting sectors who dominated discussions at COP26 will claim that the supply will grow exponentially, but as figure 1 demonstrates, this never happens in practice. Installing new energy generation equipment is complex. Not only is it a large engineering project, but it also requires societal consent on financing, location, land-rights and access, safety, legal and environmental compliance, and in many cases involves overcoming a lobby from incumbent alternatives. If the UK’s Hinckley Point C nuclear power station opens in 2026 as currently forecast, it will have taken 22 years from political commitment to operation. The UK’s Hornsey 2 offshore wind farm will have taken 16 years from political commitment to operation, when it starts this year.

These constraints are for familiar technologies – and are highly visible in the UK at present around the site of the Sizewell nuclear reactor, where every local village is covered in posters opposing the construction of a new reactor. However, for new technologies – which includes CCS as it operates at such a small scale globally – deployment is further constrained. Both the government and the public want to understand the risks of new technologies, and it is difficult to anticipate how they will respond to the first major accident – which will inevitably occur due to human error at some point. The history of nuclear power in Germany and fracking for gas in the UK demonstrate how public resistance can slow down, or even stop, the deployment of energy technologies.

Vaclav Smil’s excellent 2014 Science paper demonstrates how all past global energy transitions have occurred at a linear rate, that can be predicted only when each technology reaches 5% of the scale of the market it is entering. Energy technologies are not like smartphones. In our own work, Sarah Nelson looked at some of the countries who have introduced new energy technologies as rapidly as possible, and found a similar limit to the rate at which they are adopted, with a long lead time from invention to the first full-scale commercial deployment.

Given that the cost of not mitigating climate change is at least a billion deaths later this century, due to starvation in countries near the equator, it therefore seems rational to be more cautious than over-optimistic about the future supply of these three critical resources. Perhaps the linear rate of growth seen in the past decade will increase, but based on all past experience, it is very difficult to believe that it will grow at more than double that rate. In the case of biomass, given that the cause of deforestation is to expand agricultural land for food production, it is rational to assume that we can afford no new expansion of biomass harvest in the search for climate mitigation options. If any biomass is to be diverted for energy production, it should come only from savings made in growing fodder, if/when global consumption of ruminant meat reduces.


Armed with the above analysis, we can now analyse the discussions at COP26. Each square dot on figure 4 represents a complete mitigation plan, compiled from combinations of the solutions in table 1, with the axes indicating total global requirements for CCS and nelectricity. There are many dots, because there are many options: for example, if we continue to generate electricity with coal and gas, we need a higher capacity of CCS, where alternatively we might replace fossil fuel generations with nelectricity so need less CCS.

Figure 4: The solution space for climate mitigation discussed at COP26

The blue dots on the figure demonstrate the least extreme solutions. The green dots assume vehicle fuel, whether petrol, diesel or kerosene, is replaced by bio-fuel, which reduces the demand for nelectricity and CCS as shown, but places an impossible burden on the world’s plants. Only replacing aviation fuel with biokerosene would require an additional harvest of 200kg per person per year – double our total production for food. If all transport fuels were replaced by biofuel, we would need additional harvest of 1,600 kg per person. The orange dots demonstrate the very high cost of deploying direct air capture to allow continued emissions. This approach substantially increases demand for both nelectricity and CCS.

The red-dashed lines on figure 4 demonstrate current global supplies of CCS and nelectricity. Global capacity for CCS is so small it hasn’t moved off the y-axis.

Based on the growth rates from the past decade revealed in figures 1 and 2, and assuming that growth rates are unlikely to more than double, the purple shaded bars give likely ranges for the supply of the two resources in 2050.

The clear message of figure 4 is that the entire discussion of COP26 was around solutions that cannot possibly be delivered. In contrast, the yellow dot indicates the solution proposed in the UK FIRES Absolute Zero report, which describes a pathway to high quality living with no CCS, no additional demand for biomass and a 2.8 times expansion in nelectricity supply.

Discussion – consequences

The fact that all discussions at COP26 were based on fictional solutions to climate mitigation is alarming enough in itself. How can we have confidence in a leadership body that has so little grasp of physical reality?

However, the greatest concern revealed by this analysis is that perpetuating the myth of these solutions gives license to continued delay in the necessary steps to real mitigation. Today’s aeroplanes are like Bunsen burners: you put fossil fuel in one end and get greenhouse gas emissions out the other. In order to reach zero emissions by 2050, all of them have to stop flying. Same story for ships. Ruminants burp methane regardless of what they’re fed, so we have to stop farming them. There are currently no options to produce cement with no emissions, so we have 28 years to reconfigure the world’s construction industry to function without any concrete.  These restraints are probably temporary – later in the century, if we have reduced emissions to the point that we can survive without war, we may find new solutions and may have an expanded supply of nelectricity to support new solutions. But in the short and medium term, specific restraints are essential. The first requirement for living well within the restraints, is to acknowledge their reality. No such reality occurred at COP26.

There is a plausible pathway to both development in poorer countries and continued high quality living in the developed economies. But some aspects of developed life, and therefore some aspirations for development, must be different. We can live well but we won’t sufficient nelectricity, CCS and biomass to deliver technical equivalents to all today’s emitting activities. Only when we embrace that truth will we start to develop meaningful plans for real mitigation.

The details

What follows is a summary of the key evidence used to develop table 1. We invite scrutiny of these numbers and contributions of additional evidence to refine the argument of this blog – which we will continue to develop into an article for peer-review in a high level journal.

Global emissions

The proportions of emissions here are taken from the “World in Data” ( which gives proportions in 2016. These proportions have been multiplied by 51Gt CO2e, as an estimate of 2020 emissions, with the figure for aviation trebled according to the excellent paper by the combined authors of the aviation sector of the most recent IPCC report (Lee et al., 2021), to account for the additional radiative forcing from emissions released by aeroplanes at altitude. The “Word in Data” breakdown separates the process emissions of cement chemistry from the emissions associated with heat in cement kilns, so the emissions figure here is the chemical emissions doubled, approximating the analysis in Bajzelj, Allwood and Cullen (2013). The figure for “other industry” is given as the sum of the steel and cement sectors, which account for about half of all industrial emissions.

Road vehicles and (diesel) trains.

Total energy value of oil used (49.2% of 169EJ in 2019 for road vehicles, 0.8% for trains) from IEA Key World Energy Statistics page 39.  Energy content of a litre of petrol/diesel ~31MJ.  From one tonne of biomass you can extract 320 litres of biofuel (US DoE) 140-290 litres (DEFRA, 2019). Average car on sale in the UK requires either 6 litres petrol/100km or 16-20kWh/100km.  Same conversion efficiency from diesel to electric assumed for trains.  Electric trains covered under Electricity (emitting) below.

Shipping and Aviation

Total energy value of oil used (6.7% of 169EJ in 2019 for ships, 8.6% for aviation) from IEA Key World Energy Statistics page 39.  Same conversions as above used for energy content of fuels and biomass. Density of jet fuel is 800g/litre, and electricity cost of synthetic jet fuel is 24kWh/kg (Mearns, 2016), giving 19kWh/litre of synthetic fuel. Assumed the same for aviation and ship fuel.

Electricity (emitting)

Can be replaced either by CCS attached to gas/coal fired generation (albeit, real capture rate is less than 100% so this isn’t strictly zero emissions) or non-emitting.  Analysis assumes that all of this existing supply must be substituted by non-emitting electricity.

Electricity (non-emitting)

No analysis required – see figure 1 for breakdown.

Space heating

Assumed to be all gas boilers at domestic scale. Global gas consumption for 2018 is 800 billion cubic metres (IGU, 2020, figure 28), with energy density of 11kWh per cubic metre. Average yearly consumption of UK boiler is 12,500 kWh gas equivalent to 4000kwh electric heat pump.

Blast furnace Steel

Global steel production in 2020 was 1,878 Mt crude steel, of which 73.2% (=1,373 Mt) made in blast furnaces (WorldSteel, 2021). Assuming all steel emissions come from blast furnaces, they could be attached to CCS equipment (albeit with less than 100% capture), or replaced by hydrogen DRI+EAF production. The only commercial demonstrator of this being built, the Hybritt process in Sweden, reports a nelectricity requirement of 3,5MWh/tonne steel when the hydrogen is produced by electrolysis.


While there are several options for (slightly) reducing the emissions of cement, the only option at present that might deliver emissions free cement production is to rebuild all cement plants and attach them to CCS facilities.

Other industry

This sector comprises the remaining bulk materials production (in particular chemicals, plastics, paper and aluminium) along with all downstream manufacturing. As a crude approximation, assume that the emissions of steel and cement production are one half of all industrial emissions, and that the electricity required to electrify all remaining industry is equal to that required to electrify blast-furnace steel production via the Hybritt process.


COP26 announced a commitment to stop deforestation by 2030, so assume this works.


No measures were proposed to deal with these emissions, so they can be dealt with only by direct air capture.


As above


The greatest success of UK climate policy since 1990 has been to capture and burn-for-energy methane emissions at landfill sites, so assume this spreads worldwide to eliminate all waste emissions.

Direct Air Capture

In the absence of any transparent data on this process, we use numbers from Faishi et al (2019), knowing they are theoretical and optimistic estimates by a group wanting to promote direct air capture. Their survey of a range of technology options in figure 4 suggests about ~2500kWh/t to capture a stream of CO2 from the air. This must then be captured and stored underground, for which Faishi et al. give no data. Assume that one third of the electricity generated by a gas powered generation is used to operate CCS (anecdotal evidence) thus adding about 1500kWh/t for storage, giving total requirements of 4MWh/tonne for direct air capture and storage plus one tonne CCS per tonne captured.


Bajželj, B., Allwood, J. M., & Cullen, J. M. (2013). Designing climate change mitigation plans that add up. Environmental science & technology47(14), 8062-8069.

Bajželj, B., Richards, K. S., Allwood, J. M., Smith, P., Dennis, J. S., Curmi, E., & Gilligan, C. A. (2014). Importance of food-demand management for climate mitigation. Nature Climate Change4(10), 924-929.

BP (2021) Statistical Review of World Energy 2021,

DEFRA (2019) Crops Grown For Bioenergy in the UK: 2019,

Global CCS Institute (2021) Global Status of CCS 2021,

IEA (2021a) Key World Energy Statistics, 2021

IEA (2021b) World Energy Outlook, 2021.

IGU (International Gas Union) (2020), Global Gas Report 2020,

Lee, D. S., Fahey, D. W., Skowron, A., Allen, M. R., Burkhardt, U., Chen, Q., … & Wilcox, L. J. (2021). The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018. Atmospheric Environment, 244, 117834

Mearns (2016) LCOE and the Cost of Synthetic Jet Fuel,

Nelson, S., & Allwood, J. M. (2021). The technological and social timelines of climate mitigation: Lessons from 12 past transitions. Energy Policy152, 112155.

Smil, V. (2014). The long slow rise of solar and wind. Scientific American310(1), 52-57.

WorldSteel Association (2021), 2021World Steel in Figures,

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