Many pathways to staying below 1.5C delay deep cuts in carbon dioxide (CO2) emissions and rely instead on huge amounts of CO2 removal (CDR) later this century.
Land-based CDR is used extensively in the 1.5C pathways presented by the Intergovernmental Panel on Climate Change (IPCC) and also features heavily in the climate plans of many governments and businesses.
Yet the large-scale deployment of land-based CDR could come with major challenges. These include significant ecological and societal risks – particularly to biodiversity loss, food security, freshwater use and human rights, among others – which have not been comprehensively assessed.
In our new paper, published in Science, we assess the level of sustainability risks that could be triggered by the use of various different land-based CDR techniques, such as bioenergy with carbon capture and storage (BECCS) and afforestation and reforestation (A/R).
We show that risks are triggered at much lower levels of deployment than previously thought. Moreover, many of the “Paris aligned” 1.5C pathways presented by the IPCC would exceed the CDR sustainability limits defined by our evaluation.
CDR deployment in mitigation pathways
Many mitigation pathways assessed by the IPCC envisage large deployments of CDR throughout the 21st century.
This is significant because, although the IPCC is not “policy prescriptive”, these pathways – and the policy options within them – strongly shape the “solution space” as seen by policymakers when considering how to meet the goals of the Paris Agreement.
The use of CDR is particularly widespread in the pathways labelled by the IPCC as “1.5C with high overshoot”. In these pathways, emissions cuts are not fast enough to avoid breaching the carbon budget for 1.5C and global temperatures temporarily overshoot the 1.5C limit, before extensive use of CDR brings temperatures down later this century.
Within these pathways, CDR is deployed up to 2050 to help compensate for a slower transition away from fossil fuels, to reduce net emissions. When emissions reach net-zero, CDR is being used to counterbalance large remaining residual emissions. Beyond this point, it is used to draw-down global temperature after exceeding 1.5C.
This type of pathway is typified by the IPCC’s “Neg” illustrative mitigation pathway. Here, – some 5.1bn tonnes of CO2 (GtCO2) is taken out of the atmosphere using CDR in 2050 and 15.1GtCO2 in 2100.
In this pathway, one of five outlined in the IPPC’s sixth assessment report (AR6), primary energy from fossil fuel drops only 36% below 2020 levels by 2050 and 73% by 2100, relative to 2020.
This CDR and emissions profile is in sharp contrast to the IPCC’s “Ren” pathway – which relies on rapid scale-up of renewable energy – primary energy from fossil fuel falls 85% by 2050 and 95% by 2100, relative to 2020. (IMP-Ren)
This means that this renewable energy pathway has much lower reliance on CDR, which is only used to take 2.6GtCO2 out of the atmosphere in 2050 and 3GtCO2 in 2100.
Sustainability limits
The large amounts of land-based CDR in many of the pathways assessed by the IPCC come with significant implications in terms of sustainability, with the potential for serious impacts on human livelihoods and food security.
Yet the IPCC report does not comprehensively assess the environmental feasibility of the scenarios, nor their associated sustainability risks. Nor does it put a figure on the scale of CDR that could be deployed without triggering major impacts.
To address this gap, we quantified the sustainability limits to the widespread deployment of BECCS, A/R and “nature-based” CDR, which includes limited reforestation, forest restoration, reduced forest harvest and agroforestry.
To do so, we draw from recent studies that give greater attention to the ecological, biological and societal impacts of land-based CDR.
Based on these studies, we calculated the levels of CDR deployment that would trigger “low”, “medium”, “high” and “very high” risks for sustainability. These risk levels are colour-coded from green through to dark red, for each type of land-based CDR in the figure below.
Reading from left to right, the figure shows increasing levels of CDR deployment in terms of GtCO2 removed per year. The grey bar shows the range of “technical mitigation potential” for each technique, as currently assessed by the IPCC. The upper end of this is the largest amount that could theoretically be deployed, if barriers to rapid scale-up, constraints on feasibility and sustainability risks are not taken into account.
The figure shows that sustainability risks start well below the technical mitigation potential.
For BECCS, the IPCC reports an average technical potential of 5.9GtCO2 per year. Yet we find that deploying more than 1.2GtCO2 of BECCS per year would tip over from “low risk” into “medium” or higher risk levels.
(This figure is based on BECCS plants capturing a “medium” share of their associated CO2 emissions, below 70%. For a “low” capture rate below 50%, the low-risk threshold drops to just 0.7GtCO2 per year.)
Correspondingly, BECCS would cross the high sustainability risk threshold (shown in red) if used to remove 1.3GtCO2 with a low capture rate – or 2.8GtCO2 with a medium rate.
Even these limited levels of BECCS assume significant bioenergy policy reforms that governments have not yet addressed. These include addressing gaps in emissions accounting and ensuring bioenergy is not causing deforestation, either directly or indirectly.
For A/R, the IPCC average technical potential is 3.9GtCO2 a year. Our research shows that associated sustainability risks remain low or medium below 3.8GtCO2 per year, with high risks beyond that point.
We find that nature-based CDR (which includes limited reforestation) carries the lowest sustainability risks. Deployment would trigger high risks beyond 5.1GtCO2 a year (including 3.8GtCO2 per year of non-monoculture reforestation).
Having defined risk levels for each type of CDR, we then mapped those indicators onto the amount of CDR deployed in each of the IPCC’s five “illustrative mitigation pathways” (IMPs).
(These pathways are: gradual strengthening of climate policy, GS; widespread use of CDR, Neg; low energy demand, LD; shifting pathways towards sustainable development, SP; and heavy use of renewables, Ren.)
Our results, illustrated in the table below, show that the three pathways that limit warming to 1.5C with limited to no overshoot are able to do so without greatly overstepping our sustainability risk thresholds.
In contrast, Neg limits warming in 2100 to 1.5C with high temperature overshoot, but exceeds high and even very high sustainability risk thresholds. The GS pathway only limits warming to 2C and still carries significant levels of sustainability risks.
Reading the table from top to bottom, the first set of rows list the change in CO2 emissions, energy demand and fossil fuel use in 2050 and 2100.
The second set of rows show the amount of each type of CDR deployed in 2050 and 2100, colour-coded according to our sustainability risk levels.
The third set of rows show the amount of land needed for CDR deployment – the land footprint. Again, these are colour-coded according to our sustainability risk levels.
Notably, our findings show that the amount of land needed for CDR in the Neg pathway could reach 7.2m square kilometres in 2050 and 13.3m square kilometres in 2100. For comparison, the land area of the US is just 9.1m square kilometres.
Risk assessment
Our findings suggest there is an urgent need to consider sustainability risks when choosing between different mitigation pathways.
One way to do this would be to define a “sustainable CDR budget”, as the amount of CDR that could be deployed sustainably across all CDR methods.
While our research only considered land-based CDR, alternative CDR options are also likely to come with sustainability and deployment risks, which could limit their potential. These include direct air carbon capture and storage (DACCS) or ocean-based CDR.
Another option would be for scientists to identify Paris-aligned scenarios that do not overstep sustainability limits. Our research suggests that this could be a key priority for the IPCC’s seventh assessment cycle, as well as integrating environmental risks and feasibility throughout the IPCC’s work.
Moreover, our findings suggest that delaying fossil fuel cuts, in the hope that emissions can be drawn down later this century using CDR, would come with high sustainability risks.
If, on the other hand, countries wish to account for biodiversity considerations alongside climate goals, while still limiting temperatures to 1.5C, then they would need to follow a mitigation pathway with more rapid cuts in fossil fuel use, our research suggests.
Many of these pathways include behaviour changes and reductions in energy demand.
Countries could take up our findings in their next nationally-determined contributions (NDCs) under the Paris Agreement, due in 2025. For example, they could address sustainability risks by setting separate, transparent targets for CDR, in addition to headline emissions goals.
They could also aim to limit their reliance on CDR – and its corresponding land footprint – in order to avoid climate actions that have negative consequences for their national biodiversity plans under the global biodiversity framework (NBSAPs).
The post Guest post: Heavy use of CO2 removal would trigger high sustainability risks appeared first on Carbon Brief.
Guest post: Heavy use of CO2 removal would trigger high sustainability risks
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Climate Change
DeBriefed 19 June 2026: Bonn talks end in ‘gridlock’ | Energy’s ‘new era’ | Oceans in climate negotiations
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
Bonn talks close
‘SIDE-STEPPING AND STALLING’: UN climate talks in Bonn have ended in “gridlock”, according to Climate Home News. The outlet reported on the failure to balance developing countries’ need for climate-adaptation finance with “richer nations’ desire to move forward” on emissions cuts. It added that both topics were subject to “rule 16”, meaning no agreement could be reached and work will be pushed to the COP31 summit in Turkey. Inside Climate News quoted UN climate executive secretary Simon Stiell, who said the talks had seen “side-stepping and stalling”.
JUST TRANSITION: One “glimmer of hope” came from negotiations on achieving a “just transition”, reported Euronews. The news outlet said negotiators “made headway on operationalising the Belém-Antalya mechanism”, intended to support people in the shift to a low-carbon economy. However, Politico concluded that much of the focus in Bonn had “shift[ed] to efforts outside diplomatic talks – raising questions about the future of global climate negotiations”.
‘ATTACKING SCIENCE’: Agence France-Presse reported on the EU, Switzerland and “dozens of developing nations” warning of “attacks on science” by a “small group of fossil-fuels interests” in Bonn. Table Briefings explained that “the 1.5C target is increasingly being challenged” and the role of the UN climate-science panel – the Intergovernmental Panel on Climate Change (IPCC) – in an upcoming assessment of global climate progress “remains controversial”. See Carbon Brief’s full write-up of the talks for more detail.
US-Iran deal
PRICE DROP: The US and Iran announced that they have reached an interim agreement to halt the war and reopen the strait of Hormuz, reported Bloomberg. Oil prices have fallen, as the “long-awaited deal” began the process of “eas[ing]” the global energy crisis triggered by the conflict, according to the New York Times. The Associated Press noted that high fuel prices will “likely outlast the Iran war”.
‘OIL GLUT’: The Financial Times reported that the International Energy Agency (IEA) has forecast a “glut of oil” emerging next year, if the peace deal holds. The IEA said this would allow countries to build new strategic reserves, as they “review their energy strategies and policies in response to the crisis”, according to Reuters.
‘NEW ERA’: Agence France-Presse reported that oil and gas companies have “few illusions about a return to normal for the Gulf energy industry after more than three months of blockage”. One analyst told the newswire that the war “showed the oil and gas industry that Hormuz risk is no longer just a geopolitical headline”.
Around the world
- OCEAN MONITOR: The Trump administration is “abandoning its plan” to dismantle a $368m ocean monitoring system key for tracking climate change after a “bipartisan backlash on Capitol Hill”, reported the New York Times.
- CORAL HAVEN: The New York Times covered preliminary research, presented at the Our Ocean Conference in Kenya, suggesting there could be three times as many “coral refugia” – where corals are relatively safe from climate change – than previously thought.
- BAD CREDIT: Down to Earth reported that the first carbon credits issued under the Paris Agreement’s new Article 6.4 mechanism are “facing scrutiny over alleged links to institutions controlled by Myanmar’s military junta”.
- OIL BACKTRACK: Reuters reported that oil-and-gas company Equinor has dropped a renewable-energy target and scaled back clean investments, while another Reuters story noted that Shell is selling off its offshore wind assets.
1.1 billion
The number of children facing “at least three overlapping climate hazards”, according to a new Unicef report covered by Agence France-Presse.
Latest climate research
- Including the “permafrost carbon-climate feedback” in climate models increases the chance of exceeding “tipping elements” – such as the Greenland ice sheets, Atlantic Meridional Overturning Circulation or Amazon rainforest – by up to 50% | Environmental Research Letters
- The intensity of influenza outbreaks could decline in temperate regions, but increase in tropical areas over the next century, as the climate warms | PNAS Nexus
- European snow cover has declined by 20% for December and January since the start of the industrial era, revealing an “unprecedented ongoing shrinkage of European winters” | Communications Earth & Environment
(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)
Captured
The more than 2m battery electric vehicles (BEVs), 1m “plug-in” hybrids (PHEVs) and 100,000 electric vans on UK roads are already saving drivers a total of around £3bn a year, according to new Carbon Brief analysis. This amounts to savings of more than £1,100 a year in fuel costs for each BEV driver in the UK. The analysis comes amid reports in UK media this week that the government is considering “watering down” its EV sales targets.
Spotlight
Oceans rising at UN climate talks
The state of the world’s oceans is inextricably linked to the changing climate – and many delegates at UN climate talks want to see more focus on this issue, reports Carbon Brief.
Oceans are often described as the world’s “greatest ally” against climate change – absorbing 30% of carbon dioxide (CO2) emissions and most of the heat generated by those emissions.
They are also the site of important climate solutions, such as huge offshore windfarms and the shipping industry’s transition to cleaner fuels.
At the same time, the oceans themselves present a growing danger to coastal communities and sea life due to sea level rise, marine heatwaves and ocean acidification.
These diverse issues have led to growing calls within the UN climate process for more focus on oceans. During climate negotiations this week in Bonn – known as SB64 – nations and civil society had a chance to air these views during an “ocean and climate change dialogue”.
‘Elevate action’
Oceans first entered UN climate outcomes in 2019, when the final COP25 negotiated text requested a new “dialogue” on “the ocean and climate change to consider how to strengthen mitigation and adaptation action”.
The following years saw this dialogue established as an annual event. However, the political weight of these discussions has been limited.
COP31 is being co-led by Turkey and Australia, but with Pacific islands playing a supporting role. These small islands sometimes self-identify as “large ocean states”, stressing the ocean’s centrality in their societies.
In Bonn, figures from across the presidency threw their weight behind this issue. Chris Bowen, an Australian minister and incoming COP31 “president of negotiations”, told attendees:
“Australia, Turkey and the Pacific see an important opportunity to elevate ocean-based climate action.”
Strategies and finance
The two-day dialogue in Bonn involved a series of panels, statements and breakout groups.
One of the main topics was how oceans are integrated into national climate plans under the Paris Agreement, known as “nationally determined contributions” (NDCs).
Three-quarters of the latest round of NDCs mention oceans, with conservation of “blue carbon” ecosystems the most frequently described action. (Landscapes such as mangroves can both absorb CO2 and protect coastal areas.)
Delegates also discussed alignment with the UN biodiversity process, as well as ocean finance, which currently makes up less than 1% of all climate finance.
(As discussions were taking place in Bonn, country officials also gathered in Mombasa, Kenya for the 11th Our Ocean Conference. Carbon Brief’s associate editor Giuliana Viglione attended the conference and will publish a full summary shortly.)
Developing countries were clear that many of the ocean-related actions in their NDCs would depend on receiving more financial support.
‘Political momentum’
With the backing of the COP31 presidency, delegates were hopeful about where this year’s dialogue could lead.
Charles Hamilton, an advisor for the Bahamas who spoke for the Alliance of Small Island States (AOSIS) in the dialogue, told Carbon Brief that island representatives “are not traveling thousands of miles to just talk and pat ourselves on the back”. He added:
“A dialogue that just remains a dialogue is just more talk – no action.”
Given that, he said “discussions in the dialogue must move into COP decisions and the decisions must be actioned”, noting the importance of finance.
Marina Corrêa, oceans lead at WWF-Brazil, pointed to an upcoming UN climate change Standing Committee on Finance forum as a space to ramp up pressure on ocean finance.
More broadly, she wanted to see the presidencies translate their support into a “leader-level ocean initiative” that could “mainstream” oceans across negotiations.
“We have a really interesting opportunity, in terms of political momentum,” Corrêa told Carbon Brief.
Watch, read, listen
‘HOTTER THAN HELL’: An episode of the BBC’s Rare Earth podcast titled “hotter than hell” considered the issue of extreme heat, with input from experts and “people facing up to the hottest temperatures on the planet”.
NOT BROKEN?: John Drake, a professor of ecology at the University of Georgia, wrote an essay for Aeon – also re-published as a Guardian “long read” – questioning the framing of ecosystems and climate systems “breaking down”.
ON COURSE: On his Volts podcast, US climate journalist David Roberts interviewed UK climate minister Katie White, quizzing her about whether the UK will “stay the course with its climate plans”.
Coming up
- 20-28 June: London climate action week
- 21 June: Colombia presidential runoff
- 24 June: UK Climate Change Committee progress in reducing emissions 2026 report to parliament
Pick of the jobs
- Mongabay, managing editor – Africa | Salary: Unknown. Location: Global
- Contexte, environment reporter – Brussels | Salary: €45,000-€60,000. Location: Brussels
- Climate 200, communications director | Salary: Unknown. Location: Australia
- Energy Tracker Asia, energy transition correspondent | Salary: $3,000-$4,000 per month. Location: South-east Asia (remote)
DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.
This is an online version of Carbon Brief’s weekly DeBriefed email newsletter. Subscribe for free here.
The post DeBriefed 19 June 2026: Bonn talks end in ‘gridlock’ | Energy’s ‘new era’ | Oceans in climate negotiations appeared first on Carbon Brief.
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