The UK’s Climate Change Committee published its Seventh Carbon Budget on 26 February. In this analysis, Dr Steve Smith, Executive Director of CO2RE, summarises the report and reflects on its implications for the role of greenhouse gas removals in reaching net zero in the UK. You can also read CO2RE’s reaction to the Budget here.
It’s a feature of UK climate law that every five years the Government has to set a new emissions target, known as a carbon budget. And, in doing so, it has to take on board the advice of the independent Climate Change Committee (CCC). Last week the CCC published its recommendation for the Seventh Carbon Budget – the cap on UK emissions for the period 2038–42.
The CCC underpins its advice with a set of decarbonisation pathways for the UK. These pathways come with a lot of detail (nearly 400 pages of report, a dataset and 16 pieces of supporting research, to be precise) and they will be talked about widely over the next five years.
So, here’s a summary of what the new pathways show, particularly for greenhouse gas removal, and some of my own reflections on the implications.
The overall carbon budget picture
The punchline of the CCC’s advice is the level of the carbon budget – what the pathways stack up to in terms of (net) emissions. In this new advice the CCC is recommending that the Seventh Carbon Budget should be set at 535 MtCO2e.
As you can see from Figure 1 below, that translates to annual emissions around a quarter of current levels. It’s also 87% below 1990 levels, given that UK emissions have already come down substantially.
Figure 1: Summary of UK emissions and targets, including the recommended level for the Seventh Carbon Budget. Source: CCC Seventh Carbon Budget (Figure 1)
This level is not entirely surprising. There isn’t much wiggle room between the 2050 net zero target set in law and the level of UK emissions in 2038 (provided the Sixth Carbon Budget is achieved).
But what’s more interesting is the information in the pathways underpinning that level. While the Government can choose whether or not to accept the cap recommended by the CCC, as well as how to meet it – the CCC pathways provide a yardstick for action.
A notable signal comes from the CCC’s new approach in itself. Five years ago, the CCC had several scenarios for its advice on the Sixth Carbon Budget, with a “Balanced Net Zero Pathway” flanked by others named “Headwinds”, “Tailwinds” and the like. Now, there is a single, updated Balanced Pathway plus some uncertainty analysis. The implication seems to be this: the route is increasingly clear; the optimal technologies and actions are largely settled.
Emission reductions are still the main part of the story. As shown in Figure 2 below, around 60% of the work to 2050 comes from electricity decarbonisation (through wind and solar, topped up by some nuclear, batteries, gas CCS and/or hydrogen) plus electrification of transport, heating and industry. Of the remaining reductions, about 25% is through demand (energy efficiency, walking and cycling, less meat in diets, carbon pricing of flights), 5% is nature restoration, and the rest is low-carbon fuels, CCS and engineered removals.
Removals – through nature and industry – thus play a small but crucial role. They balance out the residual emissions, providing the “net” in net zero, and open the door to further mitigation beyond 2050.
Figure 2: Sources of abatement in the Balanced Pathway. Source: CCC Seventh Carbon Budget (Figure 3)
Engineered Greenhouse Gas Removals and carbon storage
Despite greenhouse gas removals (GGR) only providing a fraction of the net zero whole, the scale-up is ambitious given the starting point. Currently, UK grasslands and woodlands are reported to be removing 27 MtCO2/yr, while engineered removals are essentially at zero.
Figure 3 shows the mix of engineered GGR in the Balanced Pathway. It starts in 2028 with energy from waste coupled to CCS. Note that carbon captured from fossil waste (such as plastics) constitutes an avoided emission rather than a removal from the air and so is not counted here; this only includes biogenic waste, because it has captured carbon recently from the atmosphere while the biomass grew. Other forms of bioenergy with CCS, or BECCS – for electricity and other end-uses such as industry and low-carbon fuels – join in soon after.
Figure 3: Engineered greenhouse gas removals in the Balanced Pathway. Source: CCC Seventh Carbon Budget (Figure 7.12.1)
Direct air carbon capture and storage (DACCS) scales up to 8 MtCO2/yr by 2050, modelled as a 50:50 split between solid sorbent and liquid solvent technologies. A further 9 MtCO2/yr direct air capture is used to make fuels for aviation and shipping (not shown here, because the carbon is not stored but returned to the air when the fuel is burned). This 17 MtCO2/yr total matches up to the lower deployment scenario in a deep-dive research piece on direct air capture published alongside the new advice.
A key determinant to the scale-up of BECCS and DACCS is the available infrastructure to transport captured CO2 and inject it underground for geological storage. This has value not only for removals but also for dealing with residual fossil CO2 emissions from cement plants, oil refineries, and power stations. The Balanced Pathway has a rapid build-out starting in 2028 and reaching over 70 MtCO2/yr by 2050 (Figure 4). In other words, the use of CO2 storage is split roughly 50:50 between emissions reduction and GGR.
Figure 4: CO2 sent into geological storage in the Balanced Pathway. Source: CCC Seventh Carbon Budget full dataset
Two new GGR kids on the block which don’t require this infrastructure are biochar and enhanced rock weathering. Both methods involve spreading material on land: either biomass that has been burned in low-oxygen conditions, or fine rock particles that mineralise CO2. Previous CCC pathways have not included these, but now the CCC judges that these might be viable options, with evidence coming not least from the UK’s GGR Demonstrators Programme.
Their visibility now in the CCC’s Pathways means biochar and enhanced weathering are more likely to be considered in policies going forward. But the CCC has added them in at a cautious combined total of 3 MtCO2/yr by 2050. This seems designed to be small enough to avoid hitting resource limits and to keep the story in other sectors undisturbed. But beyond citing a couple of studies, the report is very quiet on costs and deployment details for these methods.
Land removals and bioresources
The land also removes CO2 in the Pathway through the growth of forests, grasslands and energy crops (Figure 5). Woodland cover increases from the current 13% to 16%. This requires tree-planting rates to more than double to 37,000 hectares per year, with the carbon benefits only coming on strong in the 2040s as planted trees mature. Getting this right is the focus of another Demonstrator project.
Figure 5: Removals and emissions from land use in the Balanced Pathway. Source: CCC Seventh Carbon Budget (Figure 7.4.2)
Energy crops such as willow and miscanthus – also a Demonstrator project – add carbon to soils as well as providing biomass for energy and industry. The Pathway sees a step-change in energy crop planting, from the current high of 1,200 hectare/yr to over 38,000 hectare/yr in just over a decade.
Not only does the land help by storing CO2 from the air directly, but it also supplies biomass used to make electricity, heat, hydrogen, biofuels, biogas and biochar. Biomass comes in a variety of types and is likely to be a limited and valuable resource in a net zero world. So, the amount and type of biomass available has a bearing on the mix of low-carbon and GGR measures in pathways.
The new Balanced Pathway relies on around 130 TWh of biomass overall in 2050, as shown in Figure 6. Notably, there is a complete cessation of biomass imports by 2050, despite currently standing at nearly half of all bioenergy use (largely to fuel Drax power station, which is aiming to become a BECCS power plant).
Figure 6 – Biomass supply in the Balanced Pathway. Source: CCC Seventh Carbon Budget (Figure 7.7.3)
It is unclear whether the biomass inputs for biochar have been factored into this supply estimate. If all of the new 3 MtCO2 from biochar/weathering were to come from biochar, I estimate it would entail a biomass requirement of roughly 5–10 TWh.
That’s the new Pathway, but what are its implications? Here are a few reflections.
Reflection 1: less GGR is good news
The picture has evolved since the CCC’s last analysis five years ago, and in several good ways: the case for decarbonising is even stronger in the new era where renewables are cheap and fossil fuels are costly (thus leaving fewer residual emissions); national emissions also happen to be 55 MtCO2e/yr lower in 2023 than was expected previously, due to a few fortuitous factors including technical updates to how emissions are accounted.
This has led to a substantial reduction in the total amount of engineered removals needed for net zero in 2050, from 57 MtCO2/yr down to 36 MtCO2/yr. It is an even bigger step down from the 75–82 MtCO2/yr asked for in the previous government’s Net Zero Strategy. Still a stretch, but perhaps a less daunting one.
Linked to this lowering is the reduction in required biomass supply for 2050, now at 130 TWh when the CCC’s work five years ago indicated 250 TWh – which included 50 TWh of imports. Lower biomass requirements will generally alleviate concerns over environmental sustainability.
It is important to remember that this is just one pathway, and the CCC itself notes “there is substantial uncertainty around both the balance between removals technologies and the trade-offs between removals, low-carbon fuels, and demand management, so these shares could be different in practice.” Nevertheless, the choices to go relatively low on biomass, BECCS, DACCS, biochar and enhanced weathering all leave some contingency in case other measures fall behind, or in case we choose to go beyond net zero to net negative.
Reflection 2: the need for speed
Less daunting it may be, but there is no getting away from the fact that the Pathway requires an acceleration on multiple fronts. And this is in the context of multiple delays.
Despite targets and support policies for a number of years, UK tree planting has been under half the required level, which itself is below the level recommended by the CCC.
Expanding woodlands, growing energy crops, restoring peatlands and building homes on a crowded island like the UK means there is wide recognition of the need for an integrated land use strategy. Such a strategy has been in development by successive governments but is still not complete. A new “national conversation” on land use was launched in January.
CO2 transport and storage has endured several false starts in the UK. Plans are well developed for two industrial clusters, with the current government investing £21.7bn, but the target of capturing 20–30 MtCO2/yr by 2030 seems to have been dropped. The 2030 target of 5 MtCO2/yr for engineered GGR similarly looks in peril. Indeed, the numbers in the CCC Pathway seem to acknowledge this. Still, further delays will restrict capacity for storage by 2050 even further.
A fundamental barrier to scaling engineered GGR is commercial viability. There is almost no incentive or obligation structure in place to reward companies for removing CO2 from air, beyond a few volunteers willing to pay a premium on their carbon offsetting. Here progress is being made by government on a “contract for difference” to set a revenue stream for BECCS and DACCS. It does not, however, cover biochar or enhanced rock weathering, despite their presence in CCC and government pathways to net zero.
Reflection 3: the role for R&D
In making net zero happen there are roles for government to bring forward new and better plans and policies. There are roles for businesses to innovate and commercialise new and better products. There are roles for people to make low-carbon choices for their homes and lifestyles. And there are roles for researchers like us.
The rapid fall in costs of renewables is a success story in climate action so far. If scientists and engineers can provide further breakthroughs in areas that currently look harder and more expensive – such as aviation and agriculture and GGR – then the transition will be far more palatable to governments and citizens.
The CCC report shows that while many things are known about the transition, there are still knowledge gaps to close. The opening of the door to newer GGR methods raises questions as to how effective they really are, how to monitor them robustly, where they are best applied, and how to ensure synergies with wider social and environmental goals. These questions are being tackled here in the GGR Demonstrators Programme and elsewhere. Also, estimates of emission and removal trends in the land sector continue to bounce around as stubborn uncertainties remain, with knock-on implications for other sectors and the levels of action required to get to net zero.
There is plenty more work to do, but we have a path.
Photo by Nick Fewings on Unsplash.
