Article Contents
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
Continue Reading
An older teaching about land acknowledgement
As I have come to understand the spirit and intention of land acknowledgement, I often return to fond memories of my grandmother and her words of wisdom. She taught that the health of the places we call home comes first, because the wellbeing of the people depends on it.
In her teaching, land acknowledgement began with the land. Long before it became a paragraph read at the start of a meeting, it was a way of recognizing a homeland: its waters, its species, its seasons, and the spirit that revealed whether the place was well.
Her teaching echoes a practice found across many Indigenous Nations. Haudenosaunee gatherings, for example, have long opened with the Ohén:ton Karihwatéhkwen, the Thanksgiving Address, often translated as “the words that come before all else.” The speaker greets and gives thanks to the people, the earth, the waters, the plants, the animals, the winds, the sun, the moon and the stars. Only after everything that sustains life has been acknowledged does the gathering turn to its own business.
That order changes what an acknowledgement is for. Its purpose was to share the story of a place with neighbours and to draw them into the work of tending it. People entered the story second, as the ones responsible for what had just been named.
Understood this way, an acknowledgement does more than open a meeting. It asks us to reconsider where we stand, and what we owe the ground beneath us.
Nations among nations
In her teaching, people are one nation among many. The salmon are a nation. So are the cedars, the bison, the medicine plants, and the pollinators. Each belongs to a place, carries its own responsibilities, and offers gifts no other nation can give.
This idea of kinship runs through many Indigenous philosophies. The phrase “all my relations,” heard in ceremonies and gatherings across Turtle Island, is a reminder that family extends beyond people to the animals, plants, waters and lands that make life possible. Some Indigenous languages carry the same understanding in their grammar, speaking of many plants, animals and natural forces as living beings rather than objects.
Sovereignty, understood through this relationship, is a kind of standing more than a form of control. Each nation belongs fully to its place and carries its share of that place’s life. No nation thrives alone, and none thrives by taking over the whole.
The land is also the source of instruction. Over generations, people watched how a river valley or a stretch of prairie kept itself well: who arrived when, who fed whom, and how much could be taken before the giving stopped. In my grandmother’s telling, those observations became instructions, and those instructions helped shape law and protocol. They guided when to harvest, where to camp, how to enter a neighbour’s territory, and what was owed in return.
Indigenous legal scholars today often describe this as law that comes from the land itself, learned by watching how living systems sustain one another. A plainer name for it is knowing how to live somewhere.
The host and the guest
One of the clearest teachings in this understanding of the world is the relationship between host and guest. My grandmother invited us to recognize that relationship in the lives of plants and animals.
A host prepares the place before anyone arrives. A beaver family dams a stream, and the pond becomes a home for fish, frogs, birds and plants. A fallen tree becomes a nurse log, feeding the next generation of seedlings as it returns to the soil.
A host offers first. A flowering plant sets out nectar. A berry bush ripens fruit. These provisions come in their own season, not whenever a visitor happens to want them.
A host also makes its presence known. Birdsong, scent and the marks left along a trail tell newcomers that a place is already inhabited. The visitor does not arrive in an empty world.
The guest has responsibilities too. A guest attends to the season and to what the place can offer. A guest does not assume that everything within reach is theirs to take. A guest leaves something that helps sustain the relationship.
A bee takes nectar and carries pollen. Read through this teaching, that exchange offers an image of visiting well: receiving a gift while helping the host continue its life.
Many Indigenous harvesting protocols carry the same ethic into daily practice: ask before taking, take only what is needed, offer thanks, and leave enough for others and for the plant or animal to recover.
None of this suggests that every relationship in nature is peaceful or generous. These are ways of seeing responsibilities that people can learn to carry.
Everyone is both
No being is only a host or only a guest.
A tree makes room for other life while depending on soil, water, sunlight, fungi, and relationships beyond itself. People, too, may welcome others into their homes while remaining dependent on the larger homeland that sustains them.
The distinction between host and guest is therefore about roles, not ranks. Everyone receives. Everyone has something to give.
The question is whether the exchange sustains the place.
A visitor who takes without restraint leaves less for those who come next. A host who neglects the place has less to offer. Both have responsibilities, and neither can fulfil them alone.
This is the heart of reciprocity, a principle found across Indigenous philosophies: relationships stay healthy when gifts move in both directions. The Haudenosaunee teaching of the seventh generation extends that exchange across time, asking that decisions made today leave the place well for those not yet born.
Mutual benefit begins here, with the recognition that different beings carry different gifts and obligations.
What people carry forward
My grandmother’s teaching connects these relationships to the ways people meet their neighbours.
The host prepares a place, offers food and rest, and explains where the visitor has arrived. The guest makes themselves known, explains why they have come, listens to the terms of the visit, and brings something in return. The gift may be material. It may also be labour, knowledge, news, or a commitment to help.
Nations around the Great Lakes carried this ethic into treaty. The Dish with One Spoon, an agreement among the Haudenosaunee, Anishinaabe and allied Nations, describes shared hunting grounds as a single dish. Everyone eats from it with one spoon, takes only what they need, leaves enough for others, and keeps the dish clean. The Two Row Wampum, between the Haudenosaunee and European newcomers, shows two vessels travelling side by side on the same river, each keeping its own ways and neither steering the other.
In this understanding, acknowledgement is more than naming the people associated with a territory. It is learning enough about a homeland to behave responsibly within it.
Whose home is this? What sustains it? What laws and agreements guide our presence? What can we receive, and what must we return?
These questions make acknowledgement a relationship rather than a recital.
They also make it diplomatic. A guest who recognizes the host’s homeland recognizes that they have entered a place with its own relationships and responsibilities. A host who welcomes the guest makes room for an encounter governed by those relationships.
Neither arrives without standing. Neither arrives without obligations.
Beginning with place
I write from the shores of the Bay of Quinte. Here, the teaching asks me to begin with the water, the shoreline, and the life they sustain. Before I describe myself, I must attend to where I am.
That does not make people or history less important. It places them within the homeland that gives them meaning. The people, their laws, their agreements, and their responsibilities all belong to the place.
In a time of longer fire seasons, troubled waters, and uncertainty about what the next season will bring, this teaching asks something difficult and useful of us: pay attention before you speak.
An acknowledgement cannot tell the story of a place if the speaker has stopped noticing it.
The land came first. Beginning there again means learning to name what sustains us, and accepting that what sustains us also asks something of us.
By Rye Karonhiowanen Barberstock
Photo by Andrik Langfield on Unsplash
The post The Land Came First appeared first on Indigenous Climate Hub.
Carbon dioxide (CO2) emissions from fossil fuels and cement are projected to fall by around 0.4% in 2026 to 38.2bn tonnes of CO2 (GtCO2), according to new figures from the Global Carbon Project.
This guest post is by:
- Dr Zeke Hausfather, Carbon Brief’s climate science contributor
- Prof Pierre Friedlingstein, chair of mathematical modelling of climate systems at the University of Exeter and part of the Global Carbon Project team.
Carbon dioxide (CO2) emissions from fossil fuels and cement are projected to fall by around 0.4% in 2026 to 38.2bn tonnes of CO2 (GtCO2), according to new figures from the Global Carbon Project.
The 21st edition of the annual “global carbon budget” report, published today, says that this small decline is largely due to a 1.9% drop in emissions from oil and the energy shock triggered by the Iran conflict and the closure of the strait of Hormuz.
Emissions from coal continue to increase slightly.
The Global Carbon Project’s projections for fossil fuel and cement CO2 emissions in 2026 are preliminary, with a range that spans a fall of -1.5% to a rise of +0.6%.
This means a small increase in emissions can not be ruled out.
Emissions from land-use change, such as deforestation, are projected to rise in 2026.
This is primarily driven by peat fires and forest degradation in south-east Asia and is linked to the development of a strong El Niño event this year.
As a result, total CO2 emissions from fossil fuels and land use are projected to reach a record high of 43.3GtCO2 in 2026 – marginally above 42.8GtCO2 in 2025.
Research published alongside the report by the same team in Nature Climate Change finds that the growth in solar, wind and electric vehicles (EVs) now offsets around two-thirds of the emissions that would otherwise come from rising energy demand.
However, the deployment of these technologies is not yet enough to push global emissions into a sustained decline, according to the study.
The 2026 global carbon budget report also estimates that:
- Fossil emissions are projected to fall in China (-0.9%), the US (-1.3%) and the EU (-1.5%) in 2026, but rise by 4.4% in India.
- Oil emissions are projected to fall in every major region, with the largest drop in China (-4.6%).
- Land-use emissions averaged 4.9GtCO2 per year over 2016-25, around 21% lower than the decade before.
- Total CO2 emissions (fossil and land-use) grew by an average 0.3% per year over the past decade (2016-25), compared with 1.7% per year over the decade before.
- The remaining carbon budget to limit warming to 1.5C is 150GtCO2, or less than four years of current emissions.
- The land sink in 2025 was the highest on record, rebounding after being weakened during the 2023-24 El Niño. The current El Niño is expected to weaken the land sink in 2027.
- The concentration of CO2 in the atmosphere is set to reach 427.7 parts per million (ppm) in 2026, 54% above pre-industrial levels.
(For more on previous editions of the Global Carbon Project’s annual report, see Carbon Brief’s coverage in 2025, 2024, 2023 and 2022.)
Total emissions edge up as land-use emissions rise
Total global CO2 emissions, which combines fossil fuels and land-use change, are projected to reach a record high of 43.3GtCO2 in 2026, up from 42.8GtCO2 in 2025.
The increase in 2026 comes entirely from a projected rise in land-use emissions, which are more challenging to estimate than fossil emissions.
(Th