Question:
You are given the full text of a scientific research paper.

    Summarize the paper's key **research findings** in the style of a policy brief. Your response should:
    - Focus on the major empirical or model-based results
    - Present findings that are policy-relevant and supported by the study
    - Use concise, non-technical language with essential technical terms as needed
    - Avoid quoting directly or summarizing minor details

    Write a short, clear paragraph appropriate for the “Scientific Research Findings” section of a policy brief.

    Scientific Research Paper:
    Nature Climate Change | Volume 13 | April 2023 | 351–358
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nature climate change
https://doi.org/10.1038/s41558-022-01592-2
Article
Why residual emissions matter right now
Holly Jean Buck
  1
, Wim Carton
  2, Jens Friis Lund3 & Nils Markusson4
Net-zero targets imply that continuing residual emissions will be balanced
by carbon dioxide removal. However, residual emissions are typically not
well defined, conceptually or quantitatively. We analysed governments’
long-term strategies submitted to the UNFCCC to explore projections of
residual emissions, including amounts and sectors. We found substantial
levels of residual emissions at net-zero greenhouse gas emissions, on
average 18% of current emissions for Annex I countries. The majority of
strategies were imprecise about which sectors residual emissions would
originate from, and few offered specific projections of how residual
emissions could be balanced by carbon removal. Our findings indicate the
need for a consistent definition of residual emissions, as well as processes
that standardize and compare expectations about residual emissions
across countries. This is necessary for two reasons: to avoid projections
of excessive residuals and correspondent unsustainable or unfeasible
carbon-removal levels and to send clearer signals about the temporality of
fossil fuel use.
Nearly three-quarters of the world’s global greenhouse gas emissions
are covered by a net-zero law, policy or political pledge as of early
20221. In its simplest form, net zero involves balancing some amount
of remaining emissions with an equal amount of negative emissions
through carbon dioxide removal. This idea of achieving a ‘balance
between anthropogenic emissions by sources and removals by sinks’
was enshrined in Article 4.1 of the Paris Agreement and has become
a prominent feature of recent IPCC assessments as well as country
strategies. Net-zero targets are driven by science that indicates that
to limit warming to 1.5 °C, the world must reach net-zero CO2 emis-
sions around 2050 and net-zero greenhouse gas emissions later in
the century (2095–2100 with no or limited overshoot, 2070–2075 with
high overshoot)2.
With the advent of net zero as a concept, the category of ‘residual
emissions’ has emerged to denote emissions that are regarded as hard
to abate and will need to be compensated via carbon removal. In the
integrated modelling literature, residual emissions may be defined as
those whose abatement remains uneconomical or technically infeasible
under the assumptions of a specific model and mitigation scenario3.
From a governance or territorial standpoint, for example as stated in
the city of San Francisco’s climate plan, residual emissions are simply
those “that remain due to limited existing options to eliminate or
reduce them further”.4 For corporations, residual emissions may be
defined in terms of the value chain; there may be emissions outside of
the scope of the company’s direct control.
Countries are currently detailing their strategies for how to reach
net-zero goals, which presents an opportunity to understand how
they see residual emissions at net zero. Specifically, governments are
submitting long-term low-emissions development strategies (LT-LEDS)
as invited under Article 4, paragraph 19 of the Paris Agreement. These
strategies are intended as an evolving visioning exercise, with emphasis
on process rather than the resulting document5–7. The idea was that this
process could inform medium-term nationally determined contribu-
tion target setting8. Creating LT-LEDS is a highly political process, and
nations have approached it in different ways, although most have
employed both stakeholder engagement and modelling tools to create
possible pathways.
Simply reading a plan does not give immediate insight into what
sort of buy-in the plan has across different internal actors within
the government or how involved external stakeholders in different
sectors truly are, both of which bear on how seriously the country
will be implementing the plan. Nations also have different levels of
Received: 17 April 2022
Accepted: 21 December 2022
Published online: 9 March 2023
 Check for updates
1 Department of Environment and Sustainability, University at Buffalo, Buffalo, NY, USA. 2Centre for Sustainability Studies, Lund University, Lund, Sweden.
3Department of Food and Resource Economics, University of Copenhagen, Copenhagen, Denmark. 4Lancaster Environment Centre, Lancaster University,
Lancaster, UK.
 e-mail: hbuck2@buffalo.edu

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Because projections out to 2050 are generally not yet in updated official
policy documents, the LT-LEDS remain the most accessible source of
information on national expectations of amounts of residual emissions
at mid-century. These countries are the first adopters of both LT-LEDS
and net-zero targets, and their assessment and actions may set the tone
for countries that follow.
In what follows, we analyse country LT-LEDS strategies to examine
four key questions. (1) How are residual emissions defined? (2) What
amounts are countries projecting? (3) How are residual emissions
distributed among sectors? (4) What are the expectations around the
land sector’s ability to compensate for residual emissions?
Definition of residual emissions
Our analysis of the 50 LT-LEDS shows that there is no consistent defini-
tion or use of the concept of residual emissions. A majority of LT-LEDS
do not explicitly mention the concept of residual emissions, despite
having a net-zero target. Few countries provide an explicit definition
or elaborate how residual emissions amounts are arrived at, explain
what criteria were used to determine them or specify what greenhouse
gases make up the residual emissions.
The examples in Table 2 illustrate the variance in how countries
describe residual emissions in LT-LEDS. Countries such as Switzerland
and Norway suggest an absolute limit on abatement options by describ-
ing residual emissions as those that ‘cannot’ be completely eliminated.
By contrast, France and Nepal exemplify a more fluid understanding,
where the need for residual emissions owes to ‘the current state of
knowledge’ and with the expectation that technological advance-
ment might change this. Sweden explicitly mentions the ambition to
minimize residual emissions as much as possible, suggesting at least
some political leverage over the amount of residual emissions allowed
in LT-LEDS. Finally, some countries make explicit reference to economic
considerations in their description of residual emissions.
We also examined the approach the countries took to projecting
residual emissions. In theory, there are two main ways to estimate the
amount of residual emissions at mid-century. The first is a top-down
approach that starts with a specified national policy target (such as 85%
or 90% of emissions from a baseline year) and either simply sets resid-
ual emissions equal to that or uses economy-wide or sector-specific
modelling to figure out how to solve for it. The second is a bottom-up
stakeholder-informed approach that estimates possible reductions
in each sector then aggregates those sectoral estimates. In principle,
a third approach is also possible—one that begins with negative emis-
sions, with either a top-down approach that starts with a target sink
capacity or a bottom-up approach that estimates the capacity for each
source of carbon removals and then projects allowable residual emis-
sions equal to that amount. However, countries are not at present using
an approach that leads with negative emissions. In our sample of 50
LT-LEDS, around one-third of countries utilized a top-down approach,
about 15% used a bottom-up approach, about 10% set residual emissions
equal to the level of forest sinks and the rest used a combined approach
or left the approach unspecified.
Amounts of residual emissions
The 18 LT-LEDS in our sample that include Annex I countries with a quan-
tification of residual emissions together project residuals of 2.2 Gt yr–1
in 2050 in their most ambitious scenarios (Fig. 1). This corresponds to
17.9% of these countries’ current emissions. Together, these countries
are currently responsible for 18% of global emissions. Should the rest
of the world make similar projections, the resulting residuals would be
over 12 Gt yr–1 (if weighted by current emissions). This sets out a need
for a substantial carbon-removal effort.
However, this figure of 12 Gt yr–1 probably underestimates the
global residual emissions that countries will be planning for. We say
this for three reasons. First, most countries included between two
and four low-carbon scenarios. For all these countries, we chose the
planning capacity—not just scientifically speaking in terms of having
forecasting tools and data, but in terms of institutional and political
possibilities to articulate a 2050 goal and explicate what would be
needed to achieve it. Costa Rica’s strategy, for example, states plainly
that achieving the structural transformation requires new tools in
terms of making political decisions and analysing what steps will be
needed to see them succeed and that traditional approaches based on
optimization models will not deliver9. It situates the LT-LEDS within a
broader development planning process, led by the Ministry of National
Planning and Economic Policy. For other countries, the LT-LEDS are not
so well integrated into planning or sustainable development institu-
tions. While in this paper we treat the outputs from these processes as
comparable, it is important to understand that they are only facets of
a deeply individual set of circumstances and processes.
The content of these strategies is more speculative than a defini-
tive ‘plan’. Most LT-LEDS present pathways—what-if explorations of
different scenarios for reaching desired targets—created using a variety
of methods. These scenarios and quantified projections inform the
strategy but are meant to be illustrative of possible futures, not predic-
tive or prescriptive10. This means that in this paper, when we discuss
a country’s estimation of residual emissions at mid-century, we are
referring to the most ambitious scenario they have offered, not their
preferred target or what they are necessarily planning for. Our sample
reflects this diversity and is characterized by different approaches to
offsetting, removal methods and target framing (Table 1).
While most countries submitted LT-LEDS in 2020 or 2021, some
countries, such as Germany and Canada, submitted their LT-LEDS a few
years ago (in 2016) and have enacted more ambitious policy since the
first iteration of their plans. The Paris Agreement and Katowice Rulebook
do not clearly specify whether LT-LEDS should be continuously
updated, although at COP-26 in 2021, countries were encouraged to
submit or update before COP-27. As of mid-2022, 51 long-term strate-
gies have been submitted; 50 were examined for this Article, of which
28 include a quantified projection of residual emissions at net zero
(in all but four cases, this is 2050). These countries are responsible for
only about a fifth of current emissions and contain few large emitters.
Table 1 | Summary of information in the long-term strategies
(N = 50)
Target framing
Year of net-zero ambition
Net zero
31
2040
1
Carbon neutral
6
2045
2
Climate neutral
6
2050
31
Emissions reduction
5
2060
1
Reduction versus business as usual
1
2065
1
Other
1
Not specified
14
Considers natural negative emissions
technologies?
Considers technological
carbon removal techniques?
Yes
36
Yes
25
No
4
No
12
Not specified
10
Not specified
13
Focus on territorial emissions only?
Use of offsetting?
Includes consumption
7
Yes
25
Territorial only
20
No
13
Not specified
23
Not specified
12
Defines residual emissions?
Quantifies residual emissions?
Yes
25
Yes
28
No or unclear
25
No
22

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scenario with the smallest number of residual emissions for this calcu-
lation. Second, most countries do not include international aviation
and shipping in their projections, both of which are commonly seen
as hard-to-abate sectors. They could represent substantial sources
of residual emissions: the International Energy Agency’s Net Zero by
2050 scenario includes 210 MtCO2 from aviation and 120 MtCO2 from
shipping, while also making strong assumptions about behavioural
change and demand reductions in aviation11. Finally, and crucially, this
calculation is derived from projections from wealthy Annex I countries,
and poorer countries may claim higher shares of residual emissions
as well as later net-zero dates. This would be in accordance with the
principle of common but differentiated responsibilities and respective
capacities12. In other words, extrapolating from the most ambitious
current projections of the world’s richest countries still gives a baseline
indication of residual emissions in the double digits.
Expectations of carbon removal via LULUCF
We examined the projected role of land use, land-use change and
forestry (LULUCF) for the 18 Annex I countries that offer estimations
of residual emissions at net zero to understand whether countries
projected that this sector would compensate for residual emissions.
The plans for future LULUCF vary in their concreteness and detail; some
include several scenarios specifying amounts of future LULUCF while
others offer only vague ideas about future mitigation through LULUCF.
Most countries expect to enhance or maintain the removal capacity
of the LULUCF sector (Table 3). For many of the countries that plan
for enhanced removals from the LULUCF sector, these removals will
equal or surpass their expected residual emissions by the point of net
zero. This is the case for, among others, Finland, Iceland, Hungary,
Latvia, Portugal, Slovakia, Spain and Sweden. However, for the biggest
emitters in the sample, expected LULUCF removals fall far short of
residuals. This is the case for Australia, Canada, France, Switzerland,
the United Kingdom and the United States. Taken together, these six
countries comprise 96% of the total residuals of the sample. As these
countries comprise the majority of residuals, their plans will be decisive
for the overall amount of residuals that will have to be removed through
means other than the LULUCF sector.
Sources of residual emissions
Of the countries with quantitative projections of residual emissions,
15 Annex I countries provide a quantitative sectoral breakdown, shown
in Fig. 2. Notably, across these countries, electricity is not responsi-
ble for many residual emissions, aligning with common expectations
that electricity is feasible to decarbonize. Agriculture and industry
represent the largest residual emissions. The prominence of agriculture
brings up the question of whether residual emissions are expected
to be CO2 or other greenhouse gases, which is unspecified in most
strategies. Only the United Kingdom includes aviation in its account-
ing of residual emissions, amounting to nearly half of its total. Notably,
these figures are mainly from Organisation for Economic Co-operation
and Development countries, and many of the non-Annex I countries
indicated that they would have residual emissions from energy.
Table 2 | Selected references to residual emissions in long-term strategies
Country
Description
Examples of references to residual emissions with varying degrees of certainty
Costa Rica
“Today, the great imperative in Costa Rica … would be to transform the emissions pattern of the economy into a net-zero emissions, or
negative emissions (i.e., removals) society, in sectors where it is possible - and very low emissions where it is not possible to reach zero. In
practice, this means that each sector will be transformed toward zero emissions, yet at different speeds.”9
Switzerland
“The emission of greenhouse gases cannot be completely eliminated in some sectors. From a current perspective, this includes
agricultural food production, some industrial processes, such as cement manufacture, and waste incineration. To achieve the net-zero goal,
these remaining emissions must be balanced by the use of technologies or processes that remove CO2 from the atmosphere and store it
permanently.”26
Iceland
“The goal of climate neutrality will not be reached without using removals of carbon from the atmosphere to compensate for emissions that
are unlikely to be eliminated.”27
Japan
“Despite the progress in energy efficiency and decarbonization in each sector, there are some sectors where CO2 emissions are unavoidable.
CO2 from those sectors can be removed by specific measures such as Direct Air Carbon Capture and Storage (DACCS), Bio-Energy with
Carbon Capture and Storage (BECCS), and forest sink measures.”28
Examples of residual emissions constrained by current state of technological knowledge
France
Glossary entry: “Near-total decarbonisation: maximum reduction of greenhouse gas emissions, the residual emissions, which are
unavoidable according to the current state of knowledge, being mainly due to agriculture, and to a lesser extent to industrial processes,
waste, domestic air transport and gas leaks (biogas, hydrogen, fluorinated gases).”12,29
Nepal
“Due to the limited capacity of current technologies, there are still emissions from energy and IPPU. However, with future technological
advancements, this can be avoided and reduced.”13,30
Examples of residual emissions delimited politically
Sweden
“[S]ome agricultural emissions are likely to remain even after 2045. These remaining emissions will need to be compensated for with
supplementary measures. It is nevertheless essential to work to ensure that these remaining emissions are as small as possible.”31
United Kingdom
“We are clear that the purpose of greenhouse gas removals is to balance the residual emissions from sectors that are unlikely to achieve full
decarbonisation by 2050, whilst not substituting for ambitious mitigation to achieve net zero. GGRs must not be pursued as a substitute for
decisive action across the economy to reduce emissions, often referred to as mitigation deterrence.”32
Examples of residual emissions defined partly in economic terms
Australia
“Additional direct emissions reductions could be enabled through a more aggressive approach to technology. Informed by the Technology
Investment Roadmap and annual LETS, Australia could focus on bringing down the costs of currently very expensive abatement
opportunities in hard-to-abate sectors like industry and agriculture.”33
United States
“In the three decades to 2050, our emissions from energy production can be brought close to zero, but certain emissions such as non-CO2
from agriculture will be difficult to decarbonize completely by mid-century … While mitigation opportunities exist for many sources of
non-CO2 GHG emissions, costs and applicability vary. Because it is challenging to eliminate all of these sources, some remaining non-CO2
emissions will need to be offset in 2050 by net-negative CO2 emissions.”34
Bold text indicates authors’ emphasis.

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The projections in country strategies cohere largely with the
sectoral breakdown of residual emissions one can find in the litera-
ture, although countries may be projecting larger amounts than in
the literature. The International Energy Agency’s Net Zero by 2050
scenario describes a largely decarbonized power sector. Out of 1.5 Gt
of residual emissions in this scenario, 40% is from heavy industries,
mainly in developing economies (chemicals, steel, cement), and 33%
is from aviation, shipping and trucks; notably, this scenario is focused
only on energy, not land.
Scenario studies analysed in the IPCC Sixth Assessment Report
(AR6)2 similarly highlight residual emissions from non-electric energy,
particularly in transport and industry (2.7.3). The AR6 also presents esti-
mations of residual GHG emissions at net zero from illustrative mitiga-
tion pathways (IMPs) (fig. SPM.5). The pathways compatible with below
1.5 °C with limited or no overshoot have residuals of 6.79 Gt (‘shifting
development pathways’, IMP-SP), 8.73 Gt (‘low demand’, IMP-LD) and
11.87 Gt (‘high renewables’, IMP-Ren), with half to two-thirds of these
from non-CO2 emissions13. In other words, analysis of net-zero and 1.5 °C
compatible pathways from the scientific literature also anticipates
that the majority of residual emissions will be from agriculture, with
some residual emissions from industry and transport. Yet estimations
of total amounts vary widely depending on scenario, and regional
analysis is limited.
Discussion
Our analysis of the LT-LEDS submitted to the UNFCCC so far shows
that (1) residual emissions do not have a standard conceptual defi-
nition; (2) countries’ projected residual emissions are a substantial
percentage of current emissions, averaging around 18% for Annex I
countries in the most ambitious scenarios; (3) while most residual emis-
sions in ambitious scenarios are indicated to come from agriculture,
industry and mobility, few countries specify sectoral breakdowns;
(4) for countries analysed, LULUCF sinks by 2050 cannot balance out
all residual emissions.
As countries look towards submitting or updating LT-LEDS in
advance of future UNFCCC events, researchers, policymakers and civil
society should work towards standardizing expectations on residual
emissions. Right now, state and non-state actors alike can self-define,
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Belgium
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Iceland
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Portugal
Slovakia
Slovenia
Spain
Sweden
Switzerland
United Kingdom
Grey: 2019 emissions
Green: projected emissions
at net zero
29.9%
16.8%
29.6%
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16.8%
16%
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18.4%
9.2%
8.7%
7%
21.4%
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19%
17.5%
15%
United States
24.5%
Emissions (MtCO2e)
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Emissions (MtCO2e)
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Emissions (MtCO2e)
Emissions (MtCO2e)
Fig. 1 | Residual emissions versus 2019 emissions, Annex I countries. The 2019 emissions are from UNFCCC inventories; total GHG emissions without LULUCF.
CO2e, CO2-equivalent.

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and claim, various amounts of residual emissions. The gift of the Paris
Agreement framework is its flexibility in exactly how countries choose
to balance sources and sinks of emissions. However, specifying residual
emissions will mitigate against the risk that governments put things
that are expensive or politically inconvenient to abate into the ‘residual
box’, thus increasing the amount of residual emissions—and thereby
creating pressures for an even larger carbon-removal infrastructure.
Concerns about the feasibility, sustainability and societal impacts
of carbon removal at several gigatons per year14,15 have led to calls to
moderate expectations of future carbon removal16. This is because
terrestrial carbon removal at the scales indicated in this Article would
require vast amounts of land and entail severe risks for food produc-
tion and/or biosphere functioning17,18 as well as the land rights and
livelihoods of rural communities and Indigenous peoples19. While
some industrial carbon-removal techniques such as direct air carbon
capture and storage have a much smaller direct land footprint, this
approach comes with large energy requirements20, which could divert
energy, and critical minerals and the associated land for renewables,
from other societal needs. Ultimately, the idea that some emissions are
hard to abate must be examined in light of these risks and challenges
with scaling carbon removal.
Many actors have called for greater clarity in net-zero targets
and plans, regarding carbon removal but also around pathways in
general12,21–23. Norms are evolving about how to develop net-zero path-
ways, as set forth in the UN Race to Zero campaign or the Science-Based
Targets Initiative. The latter sets out cross-sector and sector-specific
pathways that include a 90% reduction by 2050, with pathways that
reach a ‘low–medium’ global level of carbon removal of 1–4 Gt yr–1 in
205024. This could be an effort that sets global norms around corpo-
rate residual emissions. While we applaud the business community
and NGOs for attempting to set norms, we see a much clearer role for
governments in this area, even while acknowledging that governments
will face difficulties in this space. There is political advantage in leav-
ing residual emissions strategically ambiguous as governments need
to accommodate the interests of different sectors and regions. At the
same time, both industries and communities can benefit from certainty
in planning, and better setting out clarity and expectations around
residual emissions also has political and economic benefits.
We make the following three recommendations for policymakers
developing long-term strategies. These recommendations are also
important for the researchers and NGOs supporting their work, who
have a critical role in supporting international policymaking (Box 1).
First, include clear projections for (1) the amount of residual emis-
sions, (2) where they originate sectorally and spatially and (3) the types
of greenhouse gas. Scenarios and the graphical user interfaces used to
explore them can be made more user friendly, allowing broader engage-
ment with these key issues in climate policy. Multiscalar datasets linking
broader analysis of residual emissions to regional or facility-level data
would enable critical debates about infrastructure and enable planning
for just transitions.
Second, the policy and research communities should suggest
defined criteria by which ‘hard to abate’ should be judged. While sectors
such as aviation, steel and agriculture are commonly understood as
difficult to decarbonize, terms such as difficult, unavoidable, hard
to abate, impossible to eliminate and so on carry value judgements
about what kind of activities a society should or should not engage
in and what costs are reasonable. This normativity is unavoidable.
However, greater transparency around how emissions come to be
considered residual is critical for the legitimacy of decarbonization
efforts. Defining criteria would allow for comparison and negotiation
and the development of international norms on how to determine dif-
ficulty of abatement. This is particularly important given that what is
hard to abate changes along with technological developments, such
as green hydrogen and low-carbon aviation. Thus, assumptions and
norms around hard-to-abate emissions must be constantly revised.
The scientific community has a key role in supporting society in
defining these criteria, in terms of both creating tools and producing
research. Researchers can also produce analysis to answer the following
key questions. What processes and sectors lack technological options
for fully eliminating emissions? Are there technologies that would
become options under different policy scenarios? Where are there
opportunities for demand-side options to lower residual emissions
further, and what social factors enable and constrain those options?
These questions require interdisciplinary research, and governments
should support this research, directly funding and coordinating it as
well as being receptive to existing efforts and incorporating them into
programmes.
Third, be explicit about whether residual emissions—and net zero
as a goal—are a temporary stopgap towards a further state of decar-
bonization or a state to maintain in perpetuity. Clarity on whether
residual emissions are a temporary condition or a permanent state
is important, both for calibrating expectations for the future of the
fossil fuel sector and for understanding the intended role for carbon
removal. If negative-emission capacity is being used to compensate for
residual emissions domestically or in another country, it is not avail-
able for legacy carbon removal or coping with overshoot. Although
the AR62 frames these roles of carbon removal as complementary,
they may be in conflict if we assume carbon-removal potential will be
limited for social and sustainability reasons. Clarity on the temporal-
ity of residual emissions is also important because strategies such as
soil carbon sequestration have apparently high mid-century technical
potential, but these sinks saturate after ~20 years and require ongoing
maintenance14. Land-based sinks already accounted for may saturate
over time, as may carbon stored in products. Net zero needs to be a
durable state22, not something that might be achieved and then be
lost again. The timing of various carbon-removal strategies needs to
be better planned for, and the ability to do so hinges on understanding
Table 3 | Overview of countries’ residuals, recent and
current LULUCF35 and long-term LULUCF outlook
Country
Residuals
(MtCO2e)
2020
LULUCF
(MtCO2)
Average
2000–2020
LULUCF (MtCO2)
Long-term
LULUCF
outlook
Australia
139
−43
17
Enhance
Austria
13
−5
−7
Ambiguous
Belgium
10
−1
−2
Maintain or
enhance
Canada
149
9
−8
Enhance
Finland
9
−17
−22
Maintain or
enhance
France
80
−35
−40
Enhance
Hungary
5
−6
−4
Maintain
Iceland
1
6
6
Enhance
Latvia
4
−3
−6
Enhance
Malta
0
0
0
Maintain
Portugal
9
−8
−7
Enhance
Slovakia
7
−6
−7
Maintain
Slovenia
2
0
−5
Enhance
Spain
29
−38
−39
Maintain
Sweden
11
−37
−39
Enhance
Switzerland
68
−2
−2
Ambiguous
United Kingdom
76
−1
0
Enhance
United States of
America
1,605
−813
−818
Enhance

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whether net zero is a stopgap or permanent state. While governments
will have a challenging time being explicit about this, given their need
to address multiple domestic actors, the research institutions and
NGOs working in policy have more flexibility to be explicit about this
in their analyses and can spell out the implications of treating residual
emissions as continuing versus temporary.
Residual emissions need to be openly analysed in both science and
politics because the stakes of continuing to treat residual emissions
as a technocratic matter are high. Large and unsubstantiated claims
on residual emissions will undermine mitigation. Moreover, failing
to decide and agree on residual emissions, and instead allocating
them according to simple market logics, means that more-powerful
0
0.2
0.4
0.6
0.8
1.0
Total
Other GHGs
International
aviation and shipping
Agriculture
Industry
Waste
Buildings
Transport
Electricity
Energy
United States
United Kingdom
Switzerland
Sweden
Spain
Slovenia
Portugal
Latvia
Hungary
France
Finland
Canada
Belgium
Austria
Australia
Fractions of total residuals (CO2e)
Country
Fig. 2 | Sectoral breakdowns of residual emissions at mid-century in the most
ambitious scenarios. Data are for Annex I countries that featured projections
with quantified sectoral breakdowns. Year depicted is 2050 for all countries
besides Sweden, which has projections for 2045 when it reaches net zero. Finland
has a target of net zero at 2035 but includes projections for 2050. Note that some
countries group electricity and transport into energy, and the United States does
not report agriculture but rather CO2 and other GHGs.
Box 1
Emerging research areas for international net-zero policy
International policy efforts are needed to solve multiple problems
that underlie the net-zero framework. One problem is how residual
emissions and removals can be matched. Carbon-removal-focused
international cooperation efforts are absent or poorly described in
LT-LEDS, even though cross-country efforts might be the most cost
effective36,37. Some countries indicate that they may need to procure
carbon removal from abroad (Switzerland, Australia), yet no countries
indicated that they intended to produce surplus removals for global
markets. The challenge here has typically been read as (1) the need
to work out issues with market mechanisms, as Article 6 negotiations
are tackling, and (2) the need for better monitoring, reporting and
verification to make exchangeable removals credible38–42. Both of
these are serious challenges.
However, there is another pressing international policy need
to create safeguards against dynamics where countries expect to
acquire removals in developing countries, creating rushes—for
land, terrestrial carbon storage, space for ocean carbon removal,
geological sequestration capacity or renewable resources to
power carbon-removal technologies, such as direct air capture.
A second problem is that the evolving carbon marketplaces
have no way of making sure that removals are in fact compensating
for emissions from sectors and activities that are truly hard to
abate. Alternative frameworks might have nations with similar
socioeconomic capacities striving for the same amount of ambition
in terms of decarbonizing each sector or dividing residual emissions
according to luxury and subsistence emissions43.
A third policy challenge is that from a climate-justice perspective,
wealthy countries with historical responsibility, such as the United
States, should deliver net-negative emissions sooner to allow
poorer countries some net residual emissions post 2050. However,
if such wealthy countries decide to use their capacity for carbon
removal to balance residuals in expensive but possible-to-reduce
sectors to lower the costs of meeting net-zero goals, this adds
further pressure on other countries. Moreover, the geopolitics of
carbon removal are such that some countries have greater capacity
for land-based and geologic sinks. Countries with large sinks might
seek to use them to give competitive advantages to their industrial
or agricultural sectors, with a risk of less-stringent policies for
decarbonizing those sectors. In other words, if carbon removal is a
natural resource with finite capacity, the choices a country makes
in allocating that resource have global-justice dimensions. Thus,
residual emissions can be seen as an emerging, important focal
point for climate justice and the UNFCCC negotiations, alongside
emissions reductions goals, loss and damage, and climate finance.
Researchers have an important role to play in producing a robust
foundation for those discussions.

Nature Climate Change | Volume 13 | April 2023 | 351–358
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Article
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actors (countries, sectors, companies) will claim remaining residual
emissions and corresponding negative emissions capacity, leaving
less-powerful or less-well-organized actors unable to operate or, more
likely, to continue to operate illegally. Further, the ambiguity of residual
emissions—as a temporary measure while zero-carbon technologies
are developed versus residual emissions as a long-term feature of the
energy system—risks not just confusing publics and stakeholders, but
decreasing support for net-zero targets more broadly.
These questions may seem like far-off matters in a world where
emissions have not even peaked. But 2050 is not so distant, and the
science is clear that fossil fuel production must rapidly be curtailed
and most fossil fuel reserves must remain unextracted to meet a 1.5 °C
temperature goal25. Publics, investors, planners and other decision
makers need greater clarity on the longer-term aims of net zero to
guide decisions around fossil fuel phaseout as well as what sort of
removal efforts to invest in. Future expectations act in the present: our
expectations of 2050 inform choices made today. Many actors may see
net zero as a temporary state towards a net-negative society, but this
vision is not yet evident in national strategies.
Online content
Any methods, additional references, Nature Portfolio reporting sum-
maries, source data, extended data, supplementary information,
acknowledgements, peer review information; details of author con-
tributions and competing interests; and statements of data and code
availability are available at https://doi.org/10.1038/s41558-022-01592-2.
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Nature Climate Change
Article
https://doi.org/10.1038/s41558-022-01592-2
Methods
Country long-term strategies were downloaded from the UNFCCC
and were qualitatively coded in a spreadsheet by two independent
coders, a research assistant and a member of the research team, for
the following information:
	(1)	 Type of target (for example, carbon neutrality, net zero or other)
	(2)	 Coverage of target (GHGs or CO2)
	(3)	 Year of net zero, for countries with net-zero or carbon-neutral
targets
	(4)	 Whether there is a definition of residual emissions or hard-to-
abate/remaining emissions and, if so, how it is introduced
	(5)	 Whether there is a quantitative projection of residual emissions
at net zero and, if so, what the amount is
	(6)	 Sectoral breakdowns of residual emissions
	(7)	 The source and process of generating the projections (which
approaches were used; whether they appeared to be top-down
or bottom-up; which particular models were used to generate
them)
	(8)	 Mentions of public or stakeholder consultation or engagement
In a few cases, other government documents or sources were
also used for reference, including technical annexes for government
strategies.
Percentages of current country emissions were derived from the
World Resources Institute’s Climate Watch platform at https://www.
climatewatchdata.org/ (ref. 1).
Current-year emissions were derived from the 2019 emissions listed
in UNFCCC inventories for total GHG emissions without LULUCF, at
https://unfccc.int/process-and-meetings/transparency-and-reporting/
greenhouse-gas-data/ghg-data-unfccc/ghg-data-from-unfccc.
Recent and current LULUCF data are from (ref. 35).
The coded data was used to generate the tables and figures
in the Article. The analysis is straightforward; the work was simply
in extracting the amounts of residual emissions and sectoral break-
downs because these are not presented in a standard form across
the documents, and in some cases they appear in charts but are
not well explicated in the main text of the reports.
Reporting summary
Further information on research design is available in the Nature
Portfolio Reporting Summary linked to this article.
Data availability
The data analysed in the current study are provided in Supplementary
Data 1. The majority of the relevant data was extracted from publicly
available documents available from the UNFCCC at https://unfccc.int/
process/the-paris-agreement/long-term-strategies. Percentages of
current country emissions were derived from the World Resources
Institute’s Climate Watch platform at https://www.climatewatchdata.
org. Current-year emissions were derived from the 2019 emissions
listed in UNFCCC inventories for total GHG emissions without
LULUCF, at https://unfccc.int/process-and-meetings/transparency-
and-reporting/greenhouse-gas-data/ghg-data-unfccc/ghg-data-
from-unfccc. Recent and current LULUCF data are from (ref. 35).
Acknowledgements
This work was supported by the Swedish Research Council Formas,
grant no. 2018-01686 (H.J.B. and W.C.) and grant no. 2019-01953
(all authors). We thank A. Palumbo-Compton for research assistance.
Author contributions
H.J.B. conceived the idea for the paper and led the analysis and
writing. W.C., J.F.L. and N.M. contributed to the analysis and
development of the argument. All authors contributed to drafting,
reviewing and editing the paper.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information The online version
contains supplementary material available at
https://doi.org/10.1038/s41558-022-01592-2.
Correspondence and requests for materials should be addressed to
Holly Jean Buck.
Peer review information Nature Climate Change thanks William Lamb,
Mariësse van Sluisveld and Clea Schumer for their contribution to the
peer review of this work.
Reprints and permissions information is available at
www.nature.com/reprints.

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    Scientific Research Findings:

Answer: Our results show that most countries with quantified projections are expecting large amounts of residual emissions by 2050, and that substantial carbon removal effort would therefore be needed. We found no consistent definition or use of the concept of residual emissions across the 50 long-term low-emissions development strategies (LT-LEDS) analysed. A majority of the LT-LEDS did not mention the concept of residual emissions at all, despite having a net-zero target. The Annex 1 country LT-LEDS that did quantify residual emissions at net zero projected substantial levels; on average, 18% of current emissions based on the lowest-level projections. Agriculture and industry represented the largest sources of residual emissions in the 15 Annex I countries that included sectoral breakdowns. While some countries plan for land-based removals to compensate for their residuals, the biggest emitters expect land-based removals to fall far short of residuals, indicating a need for technological removal.