Fairly sharing 1.5: national fair shares of a 1.5 °C-compliant global mitigation effort

  • Christian HolzEmail author
  • Sivan Kartha
  • Tom Athanasiou
Original Paper


The problem of fairly distributing the global mitigation effort is particularly important for the 1.5 °C temperature limitation objective, due to its rapidly depleting global carbon budget. Here, we present methodology and results of the first study examining national mitigation pledges presented at the 2015 Paris climate summit, relative to equity benchmarks and 1.5 °C-compliant global mitigation. Uniquely, pertinent ethical choices were made via deliberative processes of civil society organizations, resulting in an agreed range of effort-sharing parameters. Based on this, we quantified each country’s range of fair shares of 1.5 °C-compliant mitigation, using the Climate Equity Reference Project’s allocation framework. Contrasting this with national 2025/2030 mitigation pledges reveals a large global mitigation gap, within which wealthier countries’ mitigation pledges fall far short, while poorer countries’ pledges, collectively, meet their fair share. We also present results for individual countries (e.g. China exceeding; India meeting; EU, USA, Japan, and Brazil falling short). We outline ethical considerations and choices arising when deliberating fair effort sharing and discuss the importance of separating this choice making from the scholarly work of quantitative “equity modelling” itself. Second, we elaborate our approach for quantifying countries’ fair shares of a global mitigation effort, the Climate Equity Reference Framework. Third, we present and discuss the results of this analysis with emphasis on the role of mitigation support. In concluding, we identify twofold obligations for all countries in a justice-centred implementation of 1.5 °C-compliant mitigation: (1) unsupported domestic reductions and (2) engagement in deep international mitigation cooperation, through provision of international financial and other support, or through undertaking additional supported mitigation activities. Consequently, an equitable pathway to 1.5 °C can only be imagined with such large-scale international cooperation and support; otherwise, 1.5 °C-compliant mitigation will remain out of reach, impose undue suffering on the world’s poorest, or both.


Effort-sharing Fair shares Climate justice Equity Mitigation NDCs UNFCCC 



Climate Action Tracker


Common but differentiated responsibilities and respective capabilities


Climate Equity Reference Project


Climate Equity Reference Framework


Conference of the Parties (to the UNFCCC)


Civil society organization(s)


European Union


European Union, in its 15-member-state configuration from 1995 to 2004


European Union, in its 28-member-state configuration since 2013


Greenhouse Development Rights


Gross domestic product


Global warming potential


Intended nationally determined contribution(s)


Intergovernmental Panel on Climate Change


Nationally determined contribution(s)


Non-governmental organization


Organisation for Economic Co-operation and Development


Organization of the Petroleum Exporting Countries


Purchasing power parity




United Nations Framework Convention on Climate Change


United States of America

We see … a consultative or assessment period … in which all Parties as well as civil society and analytic bodies would have an opportunity to review and comment on proposed commitments … and a requirement … to include a short explanation of why [Parties] believe their proposed commitment is fair and adequate. [The] world will be watching how we measure up.

US Climate Envoy Todd Stern at Chatham House,

October 2013 (Stern 2013, p. 384)

1 Introduction

Given the climate change mitigation challenge, the problem of how to share the necessary global mitigation effort—between nation states, between economic sectors, between socio-economic groups within societies, etc.—arises quickly. Climate science can usefully determine greenhouse gas concentration pathways that can be shown to be consistent with certain temperature objectives (such as a return to 1.5 °C above pre-industrial levels by 2100, IPCC 2013) and construct global mitigation scenarios consistent with those concentration pathways (e.g. IPCC 2014; Rogelj et al. 2015). While much can be said about the uncertainties and value judgements involved in such pathways and scenarios (e.g. Anderson 2015; Shue 2017; Faran and Olsson 2017, in this special issue), these are often secondary in scientific debates. Ultimately, however, the global mitigation effort implied by those pathways must be distributed in some manner among nation states, or more generally, among certain actors or groups of actors. When we shift to these types of questions, principles of justice as well as ethical and moral considerations move to the fore.

Within the international climate discourse, such considerations are important for several related reasons: first, in the United Nations Framework Convention on Climate Change (UNFCCC 1992) itself, Parties have enshrined as a fundamental principle their agreement to contribute to global climate action in different ways, “on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities”, or CBDR/RC (UNFCCC 1992). Additional ethical principles underpinning the UNFCCC include, of course, the right to sustainable development (for a discussion of the evolution of this principle within international law, see Gupta and Arts 2017 in this special issue), but it is the principle of CBDR/RC that has been the pivot of most equity debates within the climate negotiations, and it is this specific notion that is at the core of this study. Further, and despite the critical importance of adaptation and loss and damage, here we largely limit our considerations to issues of equity as they relate to climate change mitigation.

Over the lifetime of the UNFCCC, the CBDR/RC principle has been implemented and interpreted in different manners. Most recently, as one expression of this principle, the Parties to the UNFCCC have tasked each other to explain why their climate action pledge “is fair and ambitious, in light of its national circumstances” (UNFCCC 2015b, 1/CP.20, para 14) when putting forward these pledges.1 While most countries have included information in their pledge submissions that purport to address this task, they have largely failed to make systematic and plausible cases in their NDC submissions for the fairness and ambition of their pledges (Swingle 2016). Most purported equity narratives included unsubstantiated or non-transparent information, and no country indicated what the application of their justification of their pledge as ambitious and fair “would mean [if applied to] all countries, in order to be in line with the long term goals in the Paris Agreement” (Winkler et al. 2017, in this special issue). Furthermore, collectively, countries have also postponed equity-based assessment of their efforts until the first global stocktake in 2023 (UNFCCC 2015a, Art. 14). Meanwhile, civil society organizations (CSO) and research groups have undertaken such examinations in their stead—thus taking up the challenge posed by Todd Stern, at the time the USA’s climate envoy, in the opening quote of this article.

As part of this special issue on Achieving 1.5 °C and Climate Justice, this article reports on the first such examination of the INDCs, specifically of those that Parties had submitted prior to the initial deadline of 1 October 2015 (UNFCCC 2015b, 1/CP.20 para 16). The resulting report (CSO Review 2015) was one of only three major, comprehensive reports that, at the time, assessed the impacts of the mitigation pledges contained in the INDCs (the others being UNEP 2015; UNFCCC 2015c). The CSO Review differed from the other two reports in two major ways: it was the only report that considered individual countries’ pledges relative to their normatively derived “fair-share obligation”, and it did so in relation to a 1.5 °C-compliant mitigation pathway (see Supplementary Text 1), whereas the others assessed the NDCs only in aggregate and only relative to a 2 °C pathway. At least one other study has since investigated individual NDCs relative to normatively derived benchmarks (Robiou du Pont et al. 2016); it did so with a substantially different approach and results.

In the following, we will briefly elaborate the Climate Equity Reference Framework (CERF), chosen by the civil society coalition (hereafter the “Equity Review coalition”) as the analytical basis for their NDC review. We will then briefly describe the role of the authors of that framework serving as analytical support to the civil society members of the Equity Review coalition. This involved, on our side, the enumeration and clarification of the ethical choices to be made in the assessment as well as their implications, and, on our partners’ side, the actual making of those choices, based on the guiding moral, ethical, and strategic foundations of their organizations and their constituencies, and their political–moral history. We will also explain the outcome of this deliberative process: the specific choices made and the “equity benchmarks” and “equity band” that resulted from them. We will then present the results of the analysis in global aggregate terms as well as for a subset of individual countries, and we will discuss these results, including in relation to the recent literature. In concluding, we will highlight that a global mitigation that succeeds in limiting warming to 1.5 °C in 2100 can only plausibly succeed when countries embrace their “dual obligations”. These are “dual” in the sense that in addition to unsupported domestic emission reductions, countries are also obliged to engage in deep international mitigation cooperation. In the context of such international cooperation, poorer countries agree to mitigation action beyond their own fair share of the global mitigation effort, while wealthier countries provide the support necessary (financial, technological, and with regard to capacity building) to undertake these efforts.

2 The Climate Equity Reference Framework

The Climate Equity Reference Framework is a generalization of the earlier Greenhouse Development Rights (GDRs) equity framework (Athanasiou et al. 2006; Baer et al. 2008; Kartha et al. 2012).2 It is an effort-sharing framework,3 assigning “fair shares” of the global climate transition effort to individual countries.4 The global mitigation effort is defined as the difference between a global baseline projection—how emissions would develop in the absence of climate action—and the selected mitigation pathway. As such, results of effort-sharing approaches such as CERF will depend on both the level of ambition assumed (e.g. 1.5 or 2 °C) and a “no policy” baseline projection (see Supplementary Text 1 for the pathway choice and Supplementary Text 2 for data sources and projection methods). For this analysis, Fig. 2 shows the assumed global baseline emission pathway (“baseline projection”) and global mitigation pathway (“CAT 1.5 °C Median Pathway”)5. The total global mitigation effort to be shared fairly among countries in 2030, for example, is 34.6 Gt CO2eq.

This mitigation effort in any given year is shared among countries in proportion to each country’s “responsibility” and “capacity”. Here, “responsibility” refers to the degree to which a country has so far contributed to the build-up of greenhouse gases in the atmosphere. “Capacity”, on the other hand, is an indicator of its economic wherewithal, a portion of which each country can reasonably be expected to mobilize towards addressing climate change, taking into account its level of need for domestic social and economic development. Each country’s measures of responsibility and capacity—both expressed as a percentage of the global total—are then straightforwardly combined (by averaging the two, or alternatively, a weighted average) into a composite “responsibility-capacity-indicator” (RCI). The RCI expresses country’s portion of the combined global responsibility and capacity and in turn determines the country’s fair share of the global effort required to address climate change.6

This framework explicitly implements three of the four dimensions of equity principles of burden-sharing frameworks that were identified by the IPCC, namely responsibility, capacity (or, ability to pay), and right to development (IPCC 2014, chapter 4.6). The fourth dimension, equality, is implemented implicitly and follows an interpretation that equality does not imply equal right to emit (Caney 2009; IPCC 2014). Rather, the framework implements equality “as requiring equal sacrifices […] by parties who are equal along some relevant dimension—[…] to the extent that parties are not equal, more responsibility […] or capacity […] would imply more obligation, all else being equal” (IPCC 2014, p. 319).

In the CERF approach, a nation’s “responsibility” in any given year is based on its cumulative emissions since a selected “start year” (1900, for example). Then, when calculating a country’s responsibility in, say, 2030, its historical (since 1900) and projected (up to 2030) emissions are considered. Similarly, a nation’s “capacity” in any given year is a measure of its ability to pay for addressing climate change and is expressed as a function of country’s projected GDP in that particular year. Even though there are other relevant dimensions of capacity discussed in the literature—for example, institutional and technological factors of capability as well as pertinent socio-economic factors (skills, literacy, health, and life expectancy of the populace; abatement and opportunity costs; access to capital, etc.) (e.g. Winkler et al. 2007; Winkler and Rajamani 2014) and political factors—there are two main reasons for choosing GDP as a measure of countries’ capacity or capability: first, GDP is strongly correlated to most, if not all, of these measures and, second, it is readily available in widely vetted data sources for all countries, covering the past and projections into the future, including data on income distributions within each country. For these reasons, we treat GDP as a suitable proxy for countries’ overall capacity to act on climate change and on mitigation in particular.

Importantly, in calculating capacity, the CERF allows for interpreting GDP in a progressive manner, analogous to the progressive consideration of income in virtually all income tax systems. It is designed to exempt income below a specified per-capita income level (set in terms of purchasing power parity, or PPP, to account for local buying power of a country’s currency). This exemption level can, for instance, be set at point that represents a “development threshold”, signifying a level of income below which people are so poor as to legitimately place development as their principle priority, and not be expected to contribute towards the costs of the climate transition. Likewise, the emissions associated with consumption below the development threshold are excluded from the calculation of responsibility.

Together, this set of definitions allows the CERF to take both income inequality between countries and income inequality within countries into account. This is because its determination of national responsibility and capacity is based on individual terms, rather than following the usual practice of merely utilizing average per-capita values for such indicators: conceptually, the CERF calculates responsibility and capacity of individuals and then aggregates those to larger units, most commonly the nation state.7 As a result, if two countries had the same average per-capita income and emissions but different levels of inequality, they would have different values of capacity and responsibility. This is because different levels of inequality imply different numbers of poorer people whose income and emissions fall below the development threshold, and are thus excluded from the capacity and responsibility calculations (for a discussion of political and practical implications of such approaches, see Rao 2014).

A country’s allocation is then given by subtracting its fair share of the global mitigation requirement from its baseline emissions. As with virtually all equity frameworks, this allocation does not necessarily correspond to its actual physical domestic emission pathway. Rather, the national pathways represent transferable, “fair-share allocations” of a single, science-based global mitigation effort. In principle, a country can be in compliance with its allocation through a combination of domestic emission reductions and enabling emission reductions outside its borders, with the specific balance of these two options determined by various factors, including ethical, political, social, technological, and cost-effectiveness considerations. Typically, physical emission pathways in wealthier, higher-emitting countries are much less demanding than the corresponding allocations pathway would suggest. This is because the high levels of capacity and responsibility in wealthy countries typically result in the assignment of large shares of the global effort, typically, more than their plausible mitigation potential (and, indeed, often more than total national emissions). Conversely, less wealthy, lower-emitting countries typically have plausible mitigation potentials that are much bigger than their allocations. This is also due to the fact that CERF applies its allocation approach immediately, without a transition period during which large allocations are grandfathered based on past emission levels, rather than the nominal equity principle [examples include variants of Contraction and Convergence (Meyer 2004; Höhne et al. 2006), or the recent implementations of various burden-sharing approaches by Robiou du Pont et al. (2016)]. This is because, for “framework[s] intended to assign transferable rights to emit, rather than actual emissions, the rationale [for such ‘transition’ periods] is questionable: the opportunity to acquire additional allocations through emissions trading or some other transfer system would allow a cost-effective transition and lessen, though not eliminate, the political challenges” of an allocation exclusively based on the nominal equity approach considered (IPCC 2014, p. 320).

For the specific parameterization of the CERF, the most salient choices are, on the responsibility side, those that determine how far back historical emissions should be considered, whether to include non-CO2 greenhouse gases and land use emissions, and whether to utilize production- or consumption-based emissions accounting. With respect to the calculation of capacity and development need, the key choices are the level of the development threshold (and whether to use such a threshold at all), as well as additional progressivity factors, such as applying gradually increasing weights to incomes as they increase above the development threshold (akin to how tax rates progressively increase with income in income tax systems). Finally, choices can be made regarding the relative weight of responsibility and capacity in the composite RCI, with the extreme choices entirely discounting one of these components, to consider the other alone as relevant to equitable effort sharing.

3 Ethical choices and their results: the equity band

This feature of the CERF—enabling users to make their own choices, based on their own ethical judgements about the appropriate value for these “equity settings” for calculating the fair shares—allowed the organizations that came together to review the fairness and ambition of NDCs8 to examine the implications of their preferences, debate them in a precise manner, and, ultimately, delineate a well-defined range of such choices they could collectively accept as morally justifiable. More can be said about the genesis of this review (e.g. Lahn 2017, in this special issue, contrasts this effort with the genesis of the effort-sharing figures of the “Bali Box” in the IPCC’s Fourth Assessment Report), but here we wish to stress that the Equity Review coalition represented, and continues to represent, a broad spectrum of perspectives and backgrounds, from large international environmental NGOs to Southern grassroots justice movements, from trade unions to development aid organizations to faith-based organizations. The organizations invited us to provide technical input in their deliberations, where we were able to explain the ethical choices, discuss their moral and political underpinning, and illustrate the impacts on the outcomes of the quantifications. It was apparent from the start that the organizations had different views regarding, for example, the appropriate time horizon for calculating historical responsibility, the specific level of the development threshold, or the treatment (in terms of progressivity factors) of incomes above it, and so it was not possible to identify a consensus on a single set of equity settings. Ultimately, two equity benchmarks were agreed upon, representing a subset of a larger universe of possible choices. These two equity benchmarks delineated an “equity band” that marked out the range of choices that coalition deemed to be plausibly defensible as fair. A third benchmark was also explored, but explicitly deprecated as being outside the acceptable equity band. It was nonetheless included for reference purposes, since it was widely felt that the choices it was based upon had an undeniable political salience (in particular, the chosen date from which historical emissions would be considered in the responsibility calculations, the “responsibility start date”).

The two bounding benchmarks of the chosen equity band utilized 1850 and 1950, respectively, as the responsibility start dates. They both used a development threshold of $7500 income per person per year (in PPP terms)9, while one of them also introduced further progressivity factors such that only incomes above a “luxury threshold” of $50,000 per person per year would be fully counted towards a country’s capacity (while a gradually decreasing weight would be applied to income below the luxury thresholds, until reaching the development threshold, below which income was fully exempted). In the accompanying figures, these equity benchmarks are labelled “1850/high-progressivity” and “1950/medium-progressivity”, respectively. The third (reference) benchmark (“1990/low-progressivity”) uses a 1990 responsibility start date and a development threshold of $2500, along with explanations as to why these choices, in the view of the organizations involved, do not represent justifiable interpretations of the CBDR/RC principles (CSO Review 2015, p. 12).

It is instructive to contrast the choices that define the boundaries of the equity band with other equity approaches that are derived, for example, from the partial categorization10 of burden-sharing approaches canvassed by the IPCC (2014, chapter 6.3). Like its predecessor, the GDRs framework, CERF, in its most common parameterization, could be seen as an example of the “responsibility-capacity-need” category in this IPCC classification, although specific choices of parameterization would also enable it to model most of the other categories. In deciding to place equal weight on both responsibility and capacity (as opposed to unequal weights, or fully discounting either), the Equity Review coalition in effect agreed that “responsibility” and “capacity” principles underlying CBDR/RC have equal ethical merit, given the historical and political–economic context. Likewise, approaches based on equality or cumulative equality of emissions were rejected as not accounting for the fact that people in different parts of the world, and in different socio-economic strata within societies, are living in fundamentally different ways, ways that are relevant to the climate problem (e.g. their responsibility and capacity) and that should not be ignored in favour of equal treatment in the context of allocation of effort. The Parties to the UNFCCC clearly recognized these ethical considerations when they agreed to enshrine the principles of CBDR/RC and differentiation of countries based on their national circumstances—and not equality—in the climate convention.

4 Results, analysis, and discussion

Based on these choices, the allocation of the global effort could be calculated for each country. Since the ethical preferences resulted in an equity band, rather than one discrete equity setting, these calculations also result in a range of allocations for each country, rather than a single value.

Figure 1 (chart and data table in panel a and panel b) presents the results of the effort-sharing calculations for a set of ten countries, showing the two benchmarks (light and dark green) that define the equity band as well as the additional reference benchmark (grey). Results for all countries are available in the Supplementary Table. The results represent each country’s fair share of the global mitigation effort in 2030, expressed in per-capita terms. They show, in other words, the amount of mitigation each country would have to undertake below its baseline scenario in 2030. The per-capita expression has been chosen here to allow better direct comparison between countries of vastly different sizes.11
Fig. 1

Comparison of mitigation fair shares and NDC pledges. a Fair share of the mitigation effort, expressed in tonnes of CO2eq per capita of mitigation in 2030 for selected countries, showing the amount that would be required for each equity benchmarks (green bars) and the additional reference benchmark (grey bars), as well as the actual mitigation pledged in the country’s NDC (unconditional, black; or conditional, brown). For the USA, 2030 NDC values are derived by linear extrapolation between its 2025 NDC and an 80% reduction in 2050 (see USA 2015). b The same data as a but with a different scale to show details for countries with relatively low per-capita mitigation target and fair shares. c–e The emissions allocations according to the equity band (shaded green) and its bounding benchmarks (yellow and blue, respectively) as well as the additional reference benchmark (dashed line), and historical and projected emissions (solid lines) as time series for USA, India, and China, as well as the unconditional (red diamond) and conditional (blue circle) NDC and Cancun pledges for these countries. Also shown are vertical reference bars for 2020, 2025, and 2030, with a red area corresponding to pledges that do not meet or exceed at least one of the equity benchmarks and a green area corresponding to pledges that do. (Color figure online)

Unsurprisingly, countries with larger per-capita historical responsibility and larger capacity, such as the USA, Japan, Europe, and Russia, have larger fair shares of the global mitigation effort under all benchmarks (and their allocations correspondingly deviate further from their baseline) than the other countries. The results under the low- and high-progressivity settings depend on a few key factors; the average income and how unequally distributed it is across the population. For Russia, Indonesia and India, for example, have greater fair shares of the effort under the less progressive benchmark because even though some of their population have incomes above the development threshold, most of those incomes are not very high above it, and thus are discounted under the higher progressivity setting. Unlike most other industrialized countries, this is true even of Russia, whose required mitigation is substantially lower (roughly half) in the higher progressivity case.12 For India and Indonesia, shifting to a less progressive definition of capacity greatly increases the fair-share mitigation effort required (by sixfold and fourfold, respectively, comparing the two equity benchmarks). For these countries, this effect is even more pronounced with the additional (grey) reference benchmark. This reflects the fact that more progressive approaches demand relatively less effort from poor people towards solving the climate problem. In other words, the effect of moving from a more progressive to a less progressive way of calculating capacity is a shift of mitigation burden from the wealthy to the poor (a more complete and detailed sensitivity analysis of the impacts of the components of the composite RCI on emissions allocations can be found in Athanasiou et al. 2014).

Panels a and b contrast these “fair-share contributions” with the mitigation pledges contained in countries’ NDCs, as submitted to the UNFCCC by 1 October 2015 (our NDC quantification approach is described in Supplementary Text 3; our data are available as Holz et al. 2017). The figure clearly shows that among the high-capacity and high-responsibility countries (USA, EU, Japan, Russia), NDCs fall far short of the fair-share contributions as bounded by the equity band. Those shortfalls are often very significant, with the USA, for example, pledging only 16–24%, the EU about 21–23% and Japan about 10% of their respective fair-share contributions. As for Russia, its NDC mitigation pledge has been assessed as zero as its NDC implies a 2030 emissions level well above any reasonable baseline assumptions.

Among the lower-capacity and lower-responsibility countries (grouped towards the right of the chart) Brazil’s pledge falls somewhat short of its fair-share contribution, representing about 68–71% thereof. For the remaining countries, at least the high ambition end of their NDC mitigation range is compliant with the equity benchmarks. However, if assessed against the additional reference benchmark, the lower ambition or unconditional NDCs of these countries (except Marshall Islands) fall short of their fair-share mitigation.

Panels c–e introduce these 2030 figures (2025 for the USA) into an emissions time series which shows absolute tons of CO2eq on the left y-axis and the already-discussed fair shares in tons of mitigation per capita on the right y-axis. In evaluating these charts, it is crucial to recall that the CERF does not calculate physical emission pathways for countries, but rather allocations of hypothetical emission rights. Actual national emissions would follow different kinds of paths, which are not traced by the equity allocations. However, since the equity framework is not in the first instance concerned with physical emissions, those are not depicted here. This is important because a careless observer could conclude that the framework accepts an unfettered increase of emissions in, for example, China and India, while requiring the USA to reduce its emissions below zero before 2030.

This leads to an important point that is also relevant for the NDC assessment: for higher-capacity and higher-responsibility countries, such as the USA, fair shares of the global emission reductions are higher, often substantially higher, than any plausible domestic emissions reductions, indeed, often higher than domestic emissions. As such, these countries, in order to fulfil their fair-share mitigation effort, would have to cooperate to achieve mitigation opportunities in other countries. This reflects the analytical potential of allocation-based effort-sharing frameworks as recognized by the IPCC: “A crucial consideration in the analysis of the aggregate economic costs of mitigation is that the mitigation costs borne in a region can be separated from who pays those costs […], effort-sharing schemes have the potential to yield a more equitable cost distribution between countries” (IPCC 2014, p. 457, emphasis added).

An appropriate way of understanding the relationship between fair shares of mitigation and physical emission reductions is that some countries’ share of global capacity and responsibility greatly exceeds their mitigation potential, while the reverse is true for other countries. Where fair shares exceed plausible mitigation potential (typically higher-capacity and responsibility countries), domestic emission trajectories will be less stringent than implied by the allocations of the equity framework. At the same time, in order to comply with their fair-share allocations, such wealthier countries have to support extraterritorial, or cooperative, mitigation elsewhere. Conversely, while fair-share allocations might seem to suggest increases in emissions for lower-capacity and lower-responsibility countries (for example China and India in Fig. 1), the need for wealthier countries to support extraterritorial mitigation implies that lower-responsibility and capacity countries must stand ready to “host” such measures. To put this differently, as a result their physical emission trajectories would be more stringent than implied by their fair-share allocations, typically including relatively near-term peaking and steep subsequent reductions. The CSO Equity Review recognizes this by stressing that “even if countries’ pledges exceed their fair share, they will have to do more—with international support—for the world to reach a below 1.5 °C or even 2 °C pathway” (CSO Review 2015, p. 2).

In this context, conditional NDCs become extremely important. Many countries have mitigation potentials that exceed the amount of mitigation that other countries can reasonably expect them to undertake with their own means (i.e. their fair share). Conditional components of NDCs allow those countries to express the precise nature and scale of the additional mitigation activities that they would be willing to pursue in excess of their own fair shares, though only with the support of other countries. Likewise, the provision of support (financial, technological, and capacity building) for implementation of these conditional NDCs moves to the centre stage when assessing the overall contributions of countries (typically wealthy ones) whose fair-share allocations are too stringent to be implemented with domestic measures alone.

Today, of course, pledges do not typically indicate how much cooperative mitigation countries intend to engage in, or how much support for such measures they intend to provide, which means that this crucial component cannot typically be considered in assessing overall contributions. This is one of the reasons why many assessments of such national pledges against effort-sharing benchmarks find them to be lacking (CSO Review 2015, 2016; Robiou du Pont et al. 2016). One recent study assessed the Cancun mitigation pledges and took those pledges in conjunction with developed countries’ public statements on their provision of climate finance (CSO Review 2016). This study concluded that even when estimating the extraterritorial mitigation impact of existing climate finance pledges under optimistic assumptions, total effort for each of the wealthier countries assessed would still fall short relative to their fair shares of global mitigation, because of the insufficient level of those finance commitments.

However, for the NDCs, this type of assessment cannot be done, since finance pledges are not available as far out as 2030. As a result, our analysis includes no international support provided by any party as part of their 2030 mitigation contribution. While we do not doubt that, in reality, some level of public finance, technology, and capacity building support will ultimately be provided, it is impossible to assess this entirely indeterminate level on a country-by-country basis. Nor is this impossibility to assess pledges the only problem, or the most serious problem, created by this lack of predictable finance. Perhaps more problematic is the fact that poor countries with high mitigation potential cannot, without real expectation of support, be expected to properly and appropriately plan for mitigation activities on the needed scale. This is evidenced, for example, by the relatively small aggregate size of conditional measures described in the NDCs (3.8 Gt CO2eq in 2030; see Fig. 2). It stands to reason that countries would be more motivated to expand the considerable effort needed to plan for additional mitigation measures in conditional components of NDCs, and more able to do so, if they have reasonable expectations that support will flow at the required scale.
Fig. 2

Global fair shares, NDC ambition, and ambition gap. The line chart shows our 1.5 °C-compliant mitigation pathway (derived from CAT 2016), historical emissions, and our baseline projections. The outlined arrows show the fair shares of global mitigation below baseline for two groups of countries and two equity benchmarks: solid outline for the 1850/high-progressivity benchmark (fair-share reductions: 28.5 and 6.3 Gt CO2eq for wealthier and poorer countries, respectively); dashed outline for the 1950/medium-progressivity benchmark (wealthier: 25.8; poorer: 9.0 Gt CO2eq). Solidly coloured arrows show mitigation implied by NDC submissions (Unlike the NDC assessments in Fig. 1, which utilize only our own quantification of NDCs (see Supplementary Text 3, and Holz et al. 2017), the NDC assessment in Fig. 2 uses a composite data set of our own NDC quantification and Meinshausen and Alexander (2016) to account for the NDCs that were submitted after the original cut-off date.); wealthier countries are assumed to implement the more stringent end of their NDC range, where applicable. “Conditional” NDCs of poorer countries only include those mitigation actions that would be implemented subject to provision of support in addition to the country’s otherwise applicable lower level of ambition. “Wealthier” and “poorer” country differentiation is by indicator-driven dynamic approach and does not match Annexes of the UNFCCC (see main text). Values may not add due to rounding. (Color figure online)

In Fig. 2, we show the global summary of our findings. Specifically, we show that the global mitigation gap between the CAT 1.5 °C pathway and the NDC-implied mitigation below our baseline projections is 14.2–18 Gt CO2eq, assuming that wealthier countries implement the more ambitious end of their range (if applicable) and depending on whether the necessary support is provided to implement the full suite of measures contained in the conditional NDCs. Incidentally, this range happens to highlight the importance of international cooperation and support: if no support is provided, a gap of more than half of the mitigation required in 2030 between baseline and 1.5 °C-compliant pathway still needs to be closed; however, if sufficient support is forthcoming for all conditional measures, more than half of the mitigation required in 2030 is implemented. This highlights the importance of provision of means of implementation support. Note that this estimate of the mitigation shortfall is in line with other recent studies that examined the mitigation gap relative to 1.5 °C-compliant emissions pathways and found a shortfall of 15–17 Gt CO2eq (UNEP 2016), 17.8–27.5 Gt CO2eq (UNFCCC 2016), and 16.8–23 Gt CO2eq (Robiou du Pont et al. 2016), respectively.13

The figure also shows the national fair shares of the global mitigation as well as the NDC-implied mitigation aggregated to two groups, “wealthier” and “poorer” countries. These labels are in essence shorthand for “high-responsibility and capacity” countries and “low responsibility and capacity countries”, respectively.14 Countries are differentiated into these groups by an indicator-driven dynamic approach. “Wealthier” countries are those whose fair shares of global mitigation in 2030 (in this case per the 1950/medium-progressivity equity benchmark settings) are larger than their estimated domestic mitigation potential, while “poorer” countries are those for whom the opposite is the case. Note that this differentiation is indicative only; domestic mitigation potential is approximated through an heuristic algorithm in which deviation from baseline of the global mitigation pathway is applied uniformly to all countries. This differentiation does not match the Annex-I/non-Annex-I dichotomy of the UNFCCC. Although a large overlap between Annex-I and “wealthier” exists (and, indeed, all Annex-II countries are classified as “wealthier” countries), the “wealthier” countries category also includes all current non-Annex-I OECD members, the Middle-Eastern OPEC states except for Iran and Iraq, wealthier Asian countries (Taiwan and Singapore), and several Latin American states. In contrast, some Eastern European Annex-I countries (Ukraine, Belarus, Bulgaria) are not members of this category (see the Supplementary Table or countries’ assignment to the categories).

The figure clearly shows that, as a group, poorer countries’ NDCs exceed their fair shares of the needed global mitigation, by a substantial margin and even if only the unconditional components of their NDCs are considered. In contrast, wealthier countries’ NDCs fall collectively far short of their fair share of mitigation. As discussed earlier, wealthier countries’ overall contributions generally have to be supplemented by support for extraterritorial or cooperative mitigation activities if they are to match their fair shares of the effort, but we have assessed such support as zero due to the lack of such support pledges. Note, however, that the previously mentioned recent study that used a similar methodological approach and parameterization to analyse the 2020 mitigation and support pledges found that taking finance pledges into account increased the sum of mitigation and support pledged by developed countries by only about 10% compared to domestic mitigation pledges alone (CSO Review 2016).

Critically, this figure also shows that this overall finding remains true across a range of specific equity benchmarks. Thus, even without full agreement on the specific settings that constitute “equity”, this analysis helpfully highlights the areas where countries should concentrate their efforts to close the ambition gap: development of additional conditional mitigation measures in poorer countries and the strengthening of mitigation (both domestic and through international support) in wealthier countries.

5 Equity, international cooperation, and the implications of 1.5 °C

In the above, we have argued that mitigation cannot be coherently analysed, or indeed conceptualized, independently from mitigation support, through finance, technology transfer, and capacity building. More precisely, the effort-sharing framework we utilize in this study makes it clear that the fair-share allocations of wealthier countries would typically require mitigation that would greatly exceed the domestic mitigation potential of these countries, while the fair shares of poorer countries typically are smaller than their mitigation potential. This is a result with consequences: either much of the mitigation potential in poorer countries will not be realized and a significant mitigation gap will thus remain (placing the expressed temperature goals out of reach) or poorer countries must carry out more mitigation than their fair share would suggest. In practice, both options might come to pass, to one degree or another, with a less-than-sufficient mitigation mobilization in which, though they may do their utmost, developing countries cannot, and do not, mitigate deeply enough given their restricted resources, and lack of support, to make up for the shortfall of the wealthier countries.

Since this outcome is clearly undesirable, international cooperation in mitigation moves into the centre stage as a key area of intervention. As such, the analysis suggests “dual obligations” for both wealthier and poorer countries. For wealthier countries, who as we have shown fall both collectively and individually short of pledging their fair share of the necessary global mitigation, the dual obligation consists of ambitious domestic emission reductions as well as provision of support for mitigation elsewhere, as a way to fulfil that portion of their fair share that exceeds their domestic mitigation potential.

For poorer countries, the dual obligation implied here is to implement their own fair share of the global mitigation requirement and to articulate (and ultimately host) mitigation activities that go beyond their fair share, activities that capture a greater fraction of their mitigation potential than they could tap by themselves, as a further contribution to the collective global challenge. As we have shown, collectively, poorer countries exceed the first part of their dual obligation (even though several of them fall short individually; see Fig. 1 and the Supplementary Table), but the articulation of additional, conditional mitigation measures in the current NDCs falls short of the scale of cooperative mitigation that would be required for total global mitigation to be compliant with a 1.5 °C pathway. In the words of the CSO Equity Review (2015), “what is clear from our analysis is that addressing this gap in ambition can only be done through significantly scaled up cooperation among countries, especially between developed and developing countries; […] even if countries’ pledges exceed their fair share, they will have to do more—with international support—for the world to reach a below 1.5 °C […] pathway”.

It is of course clear that the urgency of short-term mitigation is greater for 1.5 °C than for 2 °C pathways (e.g. Rogelj et al. 2015) and that therefore poorer countries need to be confident that the required scale of support will indeed be forthcoming before they can reasonably be expected to embark on the considerable effort to prepare additional mitigation measures. This urgency also suggests that, unlike prevalent thinking during the Kyoto Protocol period, international cooperative mitigation cannot be understood as a mere means for wealthier countries to implement their mitigation targets through offsets. The high rates of emissions decline that are implied by 1.5 °C-compliant pathways dictate that mitigation potential is captured everywhere on the globe, and this requires real net mitigation cooperation, while traditional offsetting provides, at best, an “emissions shifting mechanism” (Chung 2007).

An equity framework like the Climate Equity Reference Framework utilized here, which employs a hybrid indicator of the salient equity dimensions, is well suited to contribute to the equity debate since it demonstrates that when the relevant dimensions (responsibility, capacity, and need) are jointly taken into account, the broad conclusions persist independent of the specific parameterization of the calculations. And as Henry Shue (2015) has convincingly demonstrated, once the general directionality of an ethical argument for climate action is thus established, a continued case for near-term inaction cannot be supported by arguments that appeal to the grounds that the precise upper boundary of the level of action by a given country, or its total volume, is yet unknown. In this context and from an international relations standpoint, there is little reason to expect poorer countries to mobilize capacities that they do not have (or that should be properly prioritized for poverty eradication) if wealthier countries are not already seen to be straining towards implementing their fair share of the global mitigation effort, in terms of both domestic reductions and international cooperation.

All this points towards the overall conclusion that the level of ambition required for a 1.5 °C pathway requires an unprecedented degree of urgent international mitigation cooperation: with poorer countries hosting and wealthier countries supporting international cooperative mitigation. And this, in turn, points towards the central role of equity and climate justice in the context of a global effort towards limiting warming to 1.5 °C, since such cooperation only seems plausible within a setting wherein everybody is seen by everybody else as contributing both their utmost and their equitable share. After all, as noted above, “the evidence suggests that outcomes seen as equitable can lead to more effective cooperation” (IPCC 2014, p. 5).


  1. 1.

    At the nineteenth Conference of the Parties of the UNFCCC, COP19, these unilaterally determined pledges were first called “intended nationally determined contributions”, or INDCs (UNFCCC 2013, 1/CP.19, para 2). In the context of the Paris Agreement (UNFCCC 2015a), the “intended” was dropped for countries that have ratified the Agreement, resulting in NDCs. Currently, the majority of UNFCCC Parties have ratified the Agreement, causing NDCs to dominate over INDCs. Thus, even though this article chiefly reports on a review exercise of the INDCs submitted prior to the Paris Agreement’s adoption, we will use the term “NDC” (or “pledge”) in this article regardless of its legal status as NDC or INDC, except when to specifically refer to the original submissions of the INDCs.

  2. 2.

    The analysis and exposition of GDRs was typically presented in terms of one particular choice of equity settings, which were made a priori by the authors and then explained and justified based on a particular set of ethical arguments and value judgements. CERF is a generalization in the sense that it is based on the same framework with the same structure as GDRs, but allows for a limitless range of user-specified choices of all the available equity variables. In other words, the difference essentially is one of its flexibility, its user interface, and its pedagogic purpose. It is used as an analytical and educational platform, designed to clarify the different moral choices to be made and to calculate their impact on national fair share results. A detailed exposition of these impacts has been done elsewhere (Athanasiou et al. 2014).

  3. 3.

    In the most general terms, “burden-sharing” approaches can be categorized into two broad classes: “resource-sharing” and “effort-sharing” approaches, where the former “are aimed at applying ethical principles to establish a basis for sharing the agreed global ‘carbon budget’”, while the latter “are aimed at sharing the costs of the global climate response” (IPCC 2014, p. 319).

  4. 4.

    Even though countries are the typical unit of analysis, its generalizability allows the CERF to be applied to different levels of analysis, such as sub-national entities (for example, Canadian provinces, Holz 2014) or socio-economic strata. For simplicity, when describing the general framework and methodologies we will refer to “countries” as this is the unit of analysis here.

  5. 5.

    This analysis uses a custom disaggregation of the “CAT 1.5 °C Median Pathway”. See Supplementary Text 1 for a pathway description and reference to the pathway data.

  6. 6.

    This quantification is done with the online “Climate Equity Reference Calculator” (Kemp-Benedict et al. 2017), available at

  7. 7.

    In the practical implementation of the Climate Equity Reference Calculator (Kemp-Benedict et al. 2017), this is done by estimating income and emission distributions across a population and applying the progressivity parameters (e.g. development thresholds) to that distribution rather than to individual-level data, which is not typically available (see Kemp-Benedict et al. 2013 for technical details). Conceptually, however, responsibility and capacity are understood in individual terms and thus individual fair shares could be calculated. See, for example, the implied “tax tables” for individuals of certain income levels implied by the approach in earlier work using the GDRs framework (Kartha et al. 2008, p. 27).

  8. 8.

    The initial set of organizations that spearheaded the review is shown on the inside cover page of its report (CSO Review 2015); a full list in its appendix.

  9. 9.

    Clearly, the level where to best set a development threshold is a matter for debate. We have consistently (e.g. Baer et al. 2008) taken the position that it ought to be at least slightly higher than a global poverty line, which is about $16 per day (PPP adjusted). This figure represents the income levels where people begin to overcome the typical manifestations of poverty (low educational attainment, high relative food expenditures, malnutrition, high infant mortality), according to empirical analysis (Pritchett 2003, 2006). According to Pritchett, “if the poverty line were defined as the level of income at which people typically achieve acceptable levels of the Millennium Development Goal indicators (such as universal primary school completion), it would be set at about [$16] a day” (Pritchett 2006, p. 13) which “is justifiable, more consistent with international fairness, and is a better foundation for […] poverty reduction” (Pritchett 2003, p. 3).

  10. 10.

    It is important to recall, and the IPCC authors themselves recognized this, that this categorization is incomplete and by no means an authoritative, ethically robust catalogue of equity approaches. This is because it was based on an opportunistic ensemble of burden-sharing approaches previously quantified in the literature that were selected according to certain modelling criteria and “only covers a small proportion of the possible allocation approaches” (Höhne et al. 2014, p. 122). Note also that the IPCC, in that same chapter and elsewhere, explicitly acknowledges the ethical importance of other approaches, principles, and indices that are examined elsewhere in the literature, including “the relative moral relevance of consumption-based emissions as opposed to production-based emissions, survival emissions as opposed to luxury emissions, progressive as opposed to regressive allocation of mitigation costs, prioritarianism as opposed to egalitarianism, and—not least—the right to development and the critical ethical importance of the eradication of poverty” (Kartha et al. 2017).

  11. 11.

    All emissions or mitigation figures in this article include emissions and removals from land use, land use change, and forestry, as well as emissions of non-CO2 greenhouse gases.

  12. 12.

    Due to the large inequality among EU countries (especially when comparing “new” member states and the EU15), the same can be observed for the EU28, albeit much less pronounced. When investigating the EU15 separately, this effect disappears.

  13. 13.

    Some of the difference between these studies and ours can be explained by different treatment of emissions from international aviation and shipping (which only UNEP (2016) and UNFCCC (2016) include), emissions from land use, land use change and forestry (which Robiou du Pont et al. (2016) exclude), and the use of different metrics for calculating the global warming potential (GWP) of non-CO2 greenhouse gases (UNEP (2016) and UNFCCC (2016) use GWP values from the IPCC’s Fourth Assessment Report, Robiou du Pont et al. (2016), and this study utilize Second Assessment Report values). Other gap estimates (for example, UNEP 2015; UNFCCC 2015c) only assess mitigation shortfalls relative to 2 °C-compliant pathways and are therefore not suited for comparison here.

  14. 14.

    While not ideal, these labels have been chosen over the more common “developed” and “developing” in particular to indicate that these groups, and their membership, are both conceptually and in practical terms distinct from the use of developed/developing country in the UNFCCC and the Paris Agreement and do not match the Annexes of the UNFCCC.



The authors are grateful for the immensely fruitful discussions among the members of the Civil Society Equity Review coalition that are too many to name here. The Climate Equity Reference Project’s work on NDC review has been supported by grants from the Rockefeller Brothers’ Fund, Christian Aid, WWF International, and Oxfam International. The authors also gratefully acknowledge the comments received from an anonymous reviewer and the editors of this special issue. Any remaining errors of fact and opinion are, of course, ours alone.

Supplementary material

10784_2017_9371_MOESM1_ESM.pdf (357 kb)
Supplementary material 1 (PDF 356 kb)
10784_2017_9371_MOESM2_ESM.xlsx (130 kb)
Supplementary material 2 (XLSX 129 kb)


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Copyright information

© Springer Science+Business Media B.V. 2017

Authors and Affiliations

  1. 1.Climate Equity Reference ProjectBerkeleyUSA
  2. 2.Stockholm Environment InstituteSomervilleUSA
  3. 3.EcoEquityBerkeleyUSA

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