Greenhouse gas removal: How could it help the UK reach net-zero by 2050?

§ What is the UK’s greenhouse gas removal programme?

Greenhouse gas removal is a sometimes controversial topic that is, nevertheless, widely considered essential for achieving the world’s climate targets.

All scenarios mapped out by the Intergovernmental Panel on Climate Change (IPCC) for achieving the most ambitious Paris Agreement warming target of 1.5C above pre-industrial levels rely on removing carbon dioxide (CO2) from the atmosphere.

And, in its most recent report published in April, the IPCC said the use of CO2 removal is now “unavoidable”, if the world is to reach net-zero greenhouse gas emissions.

In the UK, the net-zero strategy released by the government last year includes at least 5m tonnes of CO2 (MtCO2) per year of “engineered” removals by 2030, scaling up rapidly to 23MtCO2 by 2035 and 75-81MtCO2 by 2050.

As it stands, these engineered removals – technical solutions such as bioenergy with carbon capture and storage (BECCS) and direct air carbon capture and storage (DACCS) – are essentially non-existent in the UK.

Nature-based solutions to absorb emissions, such as tree-planting, are more developed, but bring their own array of technical, political and social issues that must be overcome if they are to be scaled up in line with the nation’s net-zero aspirations.

With all of this in mind, the UK has launched a selection of funding schemes and research projects that aim to fill in some of the gaps and help scale up these technologies.

The £8.6m GGR-A [“atmosphere”] research programme, supported by three research councils and the UK government, ran from 2017 to 2021 and involved 11 separate projects examining “the many uncertainties relating to the cost effectiveness, scalability, and wider environmental and societal consequences” of negative emissions.

Following on from this, government-backed body UK Research and Innovation (UKRI) has pledged £30m to support the GGR–D [“demonstrators”] research programme, which involves five projects and a central hub at the University of Oxford over the next four years. An additional £1.5m will go towards further studies in the third year of research.

At an event on 12-13 May in London, researchers working across these projects gathered to present their findings so far. They were joined by representatives from the worlds of government, finance and business to discuss key challenges that must be addressed to scale up this fledgling sector in the UK and around the world.

§ Large-scale tree-planting and BECCS

Tree-planting received a lot of attention at the conference, with attendees highlighting the role that afforestation projects are already playing in removing CO2 from the atmosphere.

Indeed, such projects are central to most “net-zero” targets by nations and businesses. The UK, for example, has an annual goal to plant 30,000 hectares of forest each year.

As Department of Environment, Food and Rural Affair (Defra) chief science adviser Prof Gideon Henderson put it, planting trees is often seen as “the poster child for GGR…everyone seems to love it”. However, he added:

“Trees are not a panacea, they do have challenges to them…the primary one, perhaps, is that they need land.”

Tree-planting or BECCS – which involves capturing and storing CO2 from biomass combustion – are widely viewed as critical for reaching the world’s climate targets. However, as Henderson alluded to, there are a lot of questions around how to translate high-level goals into reality.

With this in mind, one of the main GGR-A projects was the Feasibility of Afforestation and BECCS for Greenhouse Gas Removal (FAB-GGR), led by Dr Nem Vaughan from the University of East Anglia. 

The project involved assessing the environmental, technical, economic, policy and societal implications and trade-offs of scaling up afforestation and BECCS to remove 1bn tonnes of CO2 each year (GtCO2/yr) and 10GtCO2/yr, respectively. Vaughan told the audience:

“This real-world complexity gets very messy very quickly and any back-of-envelope calculations you see bandied around usually are just wrong.”

She stated that the push to scale up tree-planting, in particular, is already having impacts across society – visible in the voluntary offsets market and policies such as the UK’s Environmental Land Management (ELM) schemes.

A panel discussion on day two of the conference revealed how some of these issues are playing out, including a discussion about the concerns of UK farmers. Dr Judith Thornton of Aberystwyth University linked corporations buying up land to offset their emissions with the “long and painful” history of “land-grabbing” in the UK.

Finally, one of the GGR-D projects, Perennial Biomass Crops for Greenhouse Gas Removal (PBC4GGR), explored the potential for plants such as willow and miscanthus to support BECCS in the UK.

BECCS is currently not operating at scale in the UK, but it features in the government’s net-zero strategy and the CCC’s central net-zero pathway includes 53MtCO2 being removed each year by BECCS in 2050.

Dr Jeanette Whitaker of the UK Centre for Ecology and Hydrology explained how the  PBC4GGR project aimed to address the technical and social challenges of scaling up biomass crop production, from hundreds of hectares to tens of thousands.

§ Ecosystem restoration

Restoring, preserving and managing the UK’s carbon-rich ecosystems, specifically forests and peatlands, forms a key pillar of the nation’s net-zero strategy. 

This focus is reflected in the GGR-D research programme, which includes demonstrator projects exploring woodland creation and management – NetZeroPlus – and peatland restoration – GGR Peat.

Noting the “horrendous” mistakes that had been made in the UK when planting trees in the past, NetZeroPlus project leader Prof Ian Bateman of the University of Exeter said they had been searching for a more holistic approach:

“We’re trying to get away from the single-issue decision-making that has dominated for at the very least the last 50-60 years.”

Some tree species, such as the sitka spruce often grown for timber, absorb a lot of CO2 fast, but Bateman emphasised the importance of avoiding “knee-jerk” decisions based purely on CO2 removal.

“If all you’re doing is producing the cardboard boxes of tomorrow then that carbon is going to be out in the atmosphere again pretty swiftly,” he noted.

The research team draws together people from across government and the forestry sector, aiming to identify the “right tree in the right place” by measuring carbon, modelling CO2 leakage, accounting for biodiversity impacts and integrating stakeholder input.

Planting a mix of tree species could also be key to protecting the UK’s natural carbon stores from the impacts of climate change, said Prof Richard Betts, a climate scientist involved with NetZeroPlus from the University of Exeter and the UK’s Met Office. At the sidelines of the conference, he told Carbon Brief:

“Climate change is already in the pipeline, some has already happened and more will happen. So anything we do has to be able to cope with that…If we do it in the right way and have enough different types of woodland and different tree species in different places, then it will play a role [in removing greenhouse gas emissions].”

Peatlands cover one-tenth of the land in the UK and store 3GtCO2, making them important for the nation’s climate plans. However, as GGR Peat project lead Prof Chris Evans, of the UK Centre for Ecology & Hydrology, pointed out, this is largely about damage limitation and attempting to reverse the harm that has already been done to these carbon stores.

Evans stated that this is challenging as when peatlands are drained they emit CO2 very fast, but when restored they absorb it much slower. Another issue is that methane emissions from restored peatlands can cancel out short-term CO2 uptake.

At three test sites in Wales and the north of England, Evans and his team are investigating how to shift peatlands into carbon accumulation either by accelerating restoration for upland peat, or “more like active geoengineering” in the lowlands – for example, planting high biomass monocultures and converting them to biochar.

§ Increasing soil carbon stores

One of the major themes of the UK’s GGR research programme is how to boost carbon stored in soils.

UK soils currently store 10GtCO2, but have already been heavily degraded over the past 200 years by farming and pollution – and, more recently, by climate change, according to an official report. 

Prof Pete Smith, chair of plant and soil sciences at the University of Aberdeen, is the principal investigator of the programme’s Soils Research to deliver Greenhouse Gas REmovals and Abatement Technologies (Soils-R-GGREAT) project.

On Thursday, he told the conference that the project is examining two different methods for boosting soil carbon stores: “improved land management” and “biochar”.

Improved land management can involve using more sustainable agricultural practices, reducing pollution and improving landfill, and safeguarding carbon-rich soils, such as peatlands.

Biochar, meanwhile, is carbon-rich charcoal created by the burning of organic matter in the absence of oxygen (pyrolysis). When it is sprinkled over land, it can boost soil carbon stores. (It is often suggested that biochar should be spread across agricultural land because, as well as enhancing soil carbon storage, it could enhance crop productivity.)

Both techniques may have an advantage over other types of GGR because they could come with benefits for food production and restoring wildlife, said Smith. And – unlike other GGR techniques, such as large-scale tree-planting – they do not require land-use change.

Prof Colin Snape, an engineer at the University of Nottingham, told the conference about field trials for biochar taking place in the UK. These include at a former open-cast coal mine in Cumbria, crop- and grassland areas in Wales and England’s midlands and in forests across the country.

Snape told the conference:

“The deployment programme is across arable land and forestry. We’ve got over 15 tonnes of biochar on the ground already…And we’re currently recruiting farmers for the big push in deployment which will be in late summer and autumn where we’re aiming for 100 tonnes.”

The aim of the trials is to convey the “core benefits” of biochar – carbon storage and increased crop productivity – to UK farming communities, he said.

However, he added that the “jury is very much still out” on the total GGR potential for biochar in the UK.

(The UK’s independent advisory Climate Change Committee considers biochar to be a “speculative” technology and so does not include it in its central pathway for how the UK can meet net-zero by 2050.)

§ Boosting carbon stores in agriculture

As well as boosting carbon stored in soils, the farming sector could also contribute to GGR by planting trees across croplands – a technique known as “agroforestry”, the conference heard.

Prof Martin Lukac, a researcher at the University of Reading, presented some of the results of his UK GGR project, Co-delivery of Food and Climate Regulation by Temperate Agroforestry (CALIBRE), on Thursday.

The project is trialling the inclusion of trees in cropland in Suffolk and other parts of south-east England, he told the conference:

“The government has spent many, many years paying farmers to rip trees out of the landscape and now what we are proposing is for the farmers to introduce them back in.”

According to his research, planting trees across cropland in England has the potential to remove 30MtCO2 by 2050.

However, a survey of farmers in south-east England conducted by his research team found that cost was the most cited reason for why farmers do not plant trees in cropland.

This is despite further survey results suggesting that farmers are most likely to cite maintaining the land as their primary motivation for carrying out their work, rather than making a profit.

On Friday, Liz Bowles, director of farming and land-use at the Soil Association, a UK charity which promotes organic farming, told the conference that many farmers were also “perplexed” by the government’s current stance on tree-planting in croplands. She told the conference:

“They don’t know whether they should start planting trees now. Their concern is that if they start planting trees and then they have to baseline their position in three years time, probably the majority of the carbon will then have already been captured – and they won’t have been paid for that carbon capture.”

(The government’s post-Brexit plan for agriculture, which will see farmers paid for reducing emissions and restoring nature, is yet to come into force – with the National Farmers’ Union calling for it to be delayed until 2025.)

§ Enhanced rock weathering 

Several of the projects in the UK’s GGR programme examine the potential of “enhanced rock weathering”, a technique aimed at speeding up the natural weathering process to boost carbon storage over timescales lasting millions of years.

Enhanced rock weathering works by spreading finely crushed rock over large areas of land or ocean, enhancing the weathering process and eventually leading to more carbon being washed into and stored in the ocean.

Prof Aidong Yang, an engineering scientist at the University of Oxford, is principal investigator of the project Greenhouse Gas Removal by Enhanced Weathering (GGREW).

On Thursday, he told the conference that his project was investigating whether rock materials left behind at precious metal mines could be suitable for enhanced weathering.

Further research by his team is examining whether there could be physical, chemical or biological catalysts for speeding up the weathering process further.

In addition, a separate enhanced rock weathering project led by Prof David Beerling at the University of Sheffield is examining the potential of using the technique on the UK’s agricultural land, the conference heard.

Dr Chris Pearce, a scientist involved in the project from the National Oceanography Centre, told the conference that the team had begun field trials using rock from waste quarries at sites in Wales, Devon and Hertfordshire. He told the conference:

“At all three locations, we’re going to be conducting an array of geochemical, biological and ecological assessments to validate the scalability potential of enhanced weathering and also its ecological and environmental impacts.”

He added that a recent research paper by the group, published in Nature Geoscience, found that spreading rocks over farmland has the potential to remove up to 30MtCO2 a year – 45% of what would be needed to reach net-zero in 2050.

(An influential Royal Society report published in 2018 also noted the relatively large GGR potential of enhanced rock weathering, but noted this technique is still at a “low-level of technology readiness”.)

§ Capturing CO2 directly from air

The process of removing CO2 directly from the atmosphere – known as direct air carbon capture and storage (DACCS) – was not the main topic of any of the research projects on show at the event.

In a breakout session on the first day, some participants queried the focus on land-based methods for GGR at the expense of such technological approaches.

However, DACCS was touched on in a few of the talks, notably a presentation on one of the GGR-A projects, titled “comparative assessment and region-specific optimisation of greenhouse gas removal”.

The project looked at the implications of scaling up GGR technologies and considered the energy requirements and emissions associated with their operation.

Dr Piera Patrizio of Imperial College London, who led the development of the project’s modelling framework, explained that due to the relatively low overall concentrations of CO2 in the atmosphere, removing it using DACCs required large amounts of energy. 

This could be an issue if DACCS is being undertaken in nations or regions with fossil fuel-dependent power systems, as Patrizio noted:

“Depending on the location, you actually can even get negative CO2 removal efficiency meaning that it’s…not really removing overall [emissions].”

While DACCS was a relatively small component in the GGR research programme, the conference heard from a panel of experts based in China, Germany and the US about investment in negative emissions technologies such as DACCS in their countries.

Dr Jennifer Wilcox, a carbon capture expert from the US Department of Energy, told attendees via videolink that the US has $3.5bn (£2.9bn) over the next five years invested in demonstration projects linked to carbon removal, including a range of DACCS technologies. (The UK government, for its part, has announced up to £100m investment in these technologies.)

§ Enhancing ocean carbon stores

More than a quarter of human-caused CO2 emissions are absorbed by the world’s oceans – and there are several techniques for boosting marine carbon stores that have been suggested by scientists.

Despite this, there is little mention of ocean-based techniques in the UK’s GGR programme.

Prof Gideon Henderson, chief scientific adviser at Defra, told the conference that ocean-based GGR could hold real promise for helping the UK to reach its net-zero target.

“We’re seeing very substantial new thinking about how we might do that removal…direct ocean capture – just taking the CO2 out of its dissolved form in seawater – is a technology that I think’s got a lot of potential; and the idea of blue carbon. But these are really early on in that transition from research [to practice].”

In contrast to the UK, much of Australia’s national research into GGR examines the potential of ocean-based methods, Carbon Brief reported in 2018.  

§ Removing methane from the atmosphere

While most of the talks at the conference centred on how to remove CO2 from the atmosphere, one speaker focused on methods for getting rid of another – particularly potent – greenhouse gas, namely, methane.

Prof Euan Nisbet, a researcher of methane studies from Royal Holloway University, told the conference that global leaders were starting to show a particular interest in cutting back on methane.

One reason for this is, for the past two years, scientists have logged record annual increases in atmospheric levels of methane – a spike that Nisbet has been “shocked” by.

At the COP26 climate summit in November, US president Joe Biden and European Commission president Ursula von der Leyen formally announced a pledge signed by more than 100 countries to reduce methane emissions by 30% from 2020 to 2030.

While there is a movement to reduce greenhouse emissions, it is still not clear whether efforts to remove it from the atmosphere could pay off, Nisbet told the conference:

“Methane has a lifetime of a little over nine years in the atmosphere. And, therefore, the question is: is it worth removing it?”

(By comparison, CO2 has an atmospheric lifetime of up to 1,000 years.)

To try to answer this question, Nisbet’s team have been researching where most methane emissions come from – finding concentrations of atmospheric methane are higher than expected above cow fields, oil and gas facilities and landfill sites in the UK.

His research shows that methane removal becomes “potentially worthwhile” at sites where atmospheric levels exceed 100 parts per million (ppm) – any lower than this and emissions will be dealt with by “methanotrophs”, organisms that break down methane for food found in soils, he said.

However, removing methane from the atmosphere can require a large amount of energy. In these cases, it is important to consider where this energy comes from, with renewables far preferable to highly polluting coal-fired power, he added.

In the UK, methane removal has already been taking place “for years” at landfill sites – where the gas has been piped out and used to produce electricity, he said.

He told the conference that there is “huge potential” for methane removal from landfill sites in the tropics:

“What is dramatic is tropical landfills. Much of the recent growth is coming from the tropics and sub-tropics. There are enormous landfills in very large cities, such as Kinshasa and Delhi, which are very, very poorly controlled. Just half a metre of soil puts in biological removal [by methanotrophs]. It’s very simple. It doesn’t cost much.”

§ Governance, UK policies and public perceptions

The event saw a considerable focus on not only the science of GGR, but also how to create effective policies to encourage its uptake and engage people. The second day featured representatives from government and finance weighing in on what would be required.

Prof Cameron Hepburn, an economist at the University of Oxford and one of the leaders of the CO2RE Hub, part of the GGR-D scheme, told the audience that scaling up these technologies would require “the establishment of a pretty big new industry in a pretty short timescale”.

Navraj Singh Ghaleigh, a climate law expert and member of CO2RE based at the University of Edinburgh, emphasised the importance of government support, telling Carbon Brief:

“What is holding CCS back is appropriate policies and innovation pathways to enable it to scale. In 2005 the UK was in the lead position globally, to co-develop CCS with BP in the DF1 (Peterhead-Miller) project. But serial delays and lack of financial confidence by the UK government means that the UK is now fourth in Europe to develop CCS.”

Hepburn stated that this sector would provide significant investment opportunities, but highlighted the importance of research to bring costs down and ensure that GGR is socially acceptable:

“You can have the best science and you can work out the most elegant way of taking CO2 out of the air, but if the public gets the wrong idea or they don’t like it…then it’s not going to happen.”

Dr Emily Cox, an environmental policy and social psychology expert at Cardiff University, echoed this point during a panel discussion, adding that “there is a risk at the moment that the discourse is outpacing the research a little bit”.

In the same discussion Jo Warner, deputy director of net-zero frameworks at the Department for Business, Energy and Industrial Strategy (BEIS), emphasised the importance of the UK and other nations developing a high-quality monitoring, reporting and verification (MRV) system for emissions removals:

“We need to know that negative emissions [are] really negative emissions so we are…incentivising the right things.”

Prof Jo House of the University of Bristol is leading a project in this area called GGR in the Land Sector – Addressing the Gaps (GGRiLS-Gaps). It contributes to MRV efforts by quantifying the “emissions reduction gap” between the cuts in land emissions that have been pledged by major countries and what is necessary to achieve international climate targets.

Some of the GGR research projects focused on issues with policy relevance. Assessing the Mitigation Deterrence Effects of GGRs (AMDEG), led by Dr Nils Markusson of Lancaster University, highlights the risk that focusing too much on GGR could lead to fewer emissions being directly cut.

When asked by Carbon Brief how the UK would ensure that its GGR is only prioritised to cut the most hard-to-abate emissions – such as those from aviation and heavy industry – Defra’s Henderson said:

“The way we will have to do it is by being truthful about the cost of GGRs – and if we are really doing MRV properly…they are costly ways of dealing with carbon.”

Keeping such methods costly compared to other ways of decarbonising would be the “ultimate way of policing the system”, he added.

Prof Duncan McLaren of Lancaster University, who raised this issue at the event, tells Carbon Brief there is a need for removal targets that are separate to reduction targets, as well as an independent process for defining which emissions can be offset, rather than leaving it in the hands of corporations to decide. 

He also emphasised the importance of incentives and mandates to promote removal outside of the offset market.

(McLaren explored some of these issues in a 2019 guest post for Carbon Brief.)