Fair Share in Greenpeace Bonaire

Both the ICJ and the ECtHR have recognized 1.5°C with no or limited overshoot as the relevant benchmark for assessing states’ climate obligations. At the same time, climate litigation aimed at mitigation of greenhouse gases unfolds against persistent disagreement over the fair share question: how should the remaining global carbon budget (GCB) compatible with limiting warming to 1.5°C be fairly allocated among states? Domestic courts contribute to the operationalization of this question as they review the adequacy of state mitigation efforts. Yet as the remaining GCB continues to shrink, the tension sharpens: between what science indicates is required to remain within the 1.5°C objective, and what courts may demand of political institutions within the limits of judicial review and separation of powers.

The recent Greenpeace Netherlands v. The Netherlands (Greenpeace Bonaire) case makes this tension concrete. Addressing claims that inadequate climate policies violate human rights, it is the first domestic judgement to operationalize the ECtHR’s merits standards in KlimaSeniorinnen, and one of the first since the ICJ issued its Advisory Opinion on climate change. An earlier contribution described the judgement as “dialogical”: the District Court balances the urgency of mitigation with judicial restraint by foregrounding procedural and justification duties, while referring the substantive determination of revised targets and measures back to the state.

This contribution highlights how that judicial strategy, and the substantive discretion it preserves, interacts with scientific insights reflected and not reflected in the judgment. It argues that, if states are to meet their international commitment to the 1.5°C target with no or limited overshoot, climate science shows that this discretion is already significantly constrained.

How to Fairly Allocate the Remaining Global Carbon Budget?

The fair share debate fundamentally underlies domestic mitigation cases, as courts delineate the scope of discretion afforded to states in implementing their climate obligations. While international law does not prescribe a single allocation formula, it requires states to exercise “stringent due diligence” in implementing mitigation measures capable of contributing to the 1.5°C objective, in accordance with applicable equity principles, including common but differentiated responsibilities and respective capabilities (CBDR-RC), equity, and sustainable development (¶¶245-249).

In turn, effort-sharing studies translate different ethical approaches to burden-sharing into quantitative allocations of the remaining GCB, whose size depends on estimated cumulative emissions compatible with the 1.5°C target under various modeling assumptions including the probability threshold, starting date and non-CO₂ emissions.

A state’s “fair share” refers to an allocation that reflects the equity principles of international law. A distinction can accordingly be made between effort-sharing approaches that do not reflect the equity principles of international law – including grandfathering, which allocates emissions relative to current emission levels and cost-effectiveness – and approaches that do. These include responsibility, capability, sustainable development and, more controversially, equal per capita allocations. The former preserve comparatively larger shares of the remaining carbon budget for historically high-emitting states. The latter allocate comparatively greater mitigation burdens to high-emitting developed states, crucially indicating that most have already exhausted their fair share of the remaining GCB or are close to doing so.

Justification Duties and the Space Left to the State

A Procedural Remedy with Substantive Dimensions

The present case concerns Bonaire, a Caribbean island forming part of the Netherlands as a special municipality within the Kingdom of the Netherlands. Greenpeace argued that the Netherlands failed to adequately protect Bonaire from the adverse effects of climate change, owing to insufficient mitigation and adaptation measures, and discriminatory treatment of its inhabitants. The District Court found violations of Article 8 ECHR and related non-discrimination provisions (¶¶12.1-12.3). On mitigation, it ordered the State to revise its climate policy within eighteen months, requiring adequately justified, economy-wide interim reduction targets for the period up to 2050 compatible with international law and a clear account of how its remaining emission space relates to the remaining GCB (¶12.2).

Echoing KlimaSeniorinnen (¶543), in light of the 1.5°C limit, the Court recognized a reduced margin of appreciation regarding the need and the stringency of climate objectives, and a wider margin regarding the choice of measures, provided these are reasonably capable of achieving set objectives and are actually implemented (¶¶10.21-10.22). Although framed as procedural, these obligations can be understood as having “substantive dimensions”, insofar as they must be jointly capable of staying below 1.5°C (ICJ AO ¶245).

The 43% Benchmark as a Trigger for Justification

Throughout the judgement, the Court relies on an IPCC AR6 WIII benchmark calling for a 43% reduction in global greenhouse gas emissions by 2030 relative to 2019 levels, emphasizing its international endorsement in the First Global Stocktake and the Sharm el-Sheikh Implementation Plan. This reflects a broader trend of using formally non-binding international instruments to interpret the scope of states’ mitigation obligations and a wider pattern in European climate adjudication of grounding scientific credibility in international political and scientific consensus.

Unlike in Urgenda, the District Court treats the benchmark not as a reduction floor but as a reference point, triggering a need for justification where lower domestic emission reductions are pursued (¶11.13.5). It further considers that such lower reductions do not in themselves violate Article 8 ECHR, but may weigh as a negative factor in its overall assessment, particularly where relying on contested allocation methods such as grandfathering. States may defend them by providing additional mitigation or adaptation support to other states, provided that the overall policy is adequately justified as sufficient and equitable under international law (¶11.13.4).

In principle, this reasoning allows lower domestic emission reduction targets to be justified through reductions abroad and potentially through carbon dioxide removal (CDR), although not explicitly addressed by the Court. Neither does the Court specify to what extent such measures may substitute for feasible domestic reductions, or when such reliance would be compatible with international equity standards. More fundamentally, it leaves unaddressed that such reliance on substitutability is already constrained by what climate science indicates is required to remain within the 1.5°C limit. It increases the risk of overshoot while shifting the burden of mitigation and overshoot management to other states and future generations.

Carbon Budgets and the Problem of Alternatives

A related point concerns the Court’s treatment of carbon budgeting. The District Court treats the requirement in KlimaSeniorinnen that states must quantify emission limits “through a carbon budget or otherwise” (¶573) as methodologically open (¶11.15.2). Yet Strasbourg’s reasoning arguably points to a more constrained understanding, in which alternative forms of quantification must meaningfully capture a state’s fair share of the remaining GCB. The District Court does not engage with whether alternative formulations can meet that standard in light of climate science.

Limits of the 43% Benchmark

The 43% benchmark marks the median reduction target globally required by 2030, compared to 2019 emissions levels, to remain on a pathway consistent with the remaining GCB for a >50% likelihood of limiting warming to 1.5 °C with no or limited overshoot. It is accompanied by the warning that further delaying reductions until 2030 would make it virtually impossible to stay within this budget without heavy and uncertain reliance on CDR.

A Global Average, Not an Equitable National Benchmark

Crucially, this global average is not an equitable benchmark for high-emitting developed states such as the Netherlands. As the District Court acknowledges, the equity principles of international law require so-called developed, high-emitting countries to take the lead in reducing emissions (¶11.13.5.). Regardless of how the State formally specifies its remaining emission space, effort-sharing accounts reflecting these principles indicate that high-emitting states have already exceeded, or are close to exceeding, their fair share of the GCB. Delaying or displacing feasible domestic reductions thus relies on emission space that, on many effort-sharing accounts, has already been exhausted.

How Further Delay Changes the Equation

Since the IPCC figure was endorsed in 2022, global emissions have continued to exceed the levels assumed in the underlying pathways. More recent analyses estimate that the remaining GCB is 130 GtCO₂ from 2025 for a 50% chance of limiting warming to 1.5°C, likely to be exhausted before 2030 at current rates. Emission targets are pathway dependent: the same 2030 reduction can yield very different cumulative emissions depending on interim emissions. A 43% reduction by 2030 may therefore no longer suffice to remain within a 1.5°C-consistent GCB. Consequently, the flexibility preserved by the Court is narrower than the benchmark, viewed in isolation, suggests.

The Limits of Substitution: Science and Fairness 

The Shrinking Space for Mitigation Abroad

Geophysically, limiting warming to 1.5°C depends on cumulative emissions; not where reductions occur first. In principle, therefore, financing or facilitating reductions abroad could offset slower domestic reductions. Yet as global emissions continue to rise, this compensatory space is rapidly vanishing: the more states accumulate carbon debt, the further the remaining GCB shrinks and, with it, the scope for offsetting excess domestic emissions through mitigation abroad. This creates risks of competition for the same limited reductions space abroad, and of overshoot where multiple states rely on foreign emission reductions without coordination. Reductions abroad further raise concerns of double-counting and transparency, and equity concerns where they concentrate in developing countries, potentially imposing local burdens without comparable benefits, and constraining emission space tied to development opportunities.

The Limited Space for Removals

It does, however, matter when reductions occur. If the GCB for 1.5°C is exceeded before reaching net zero, temperatures will temporarily overshoot and can only be brought back through sustained net-negative CO₂ emissions thereafter. Overshoot increases risks to human and natural systems, including the likelihood of crossing irreversible tipping points, which increase according to its magnitude and duration. This has distributional consequences, as impacts fall disproportionately on regions which have historically contributed least to cumulative emissions and are more vulnerable to climate impacts due to, inter alia, their geographical position and limited resources. Consequently, pathways for 1.5°C with no or limited overshoot require rapid emission reductions in the near-term, and restrict CDR before net zero to balancing residual emissions, with larger scale deployment only thereafter (IPCC C.1-C.3; European Scientific Advisory Board on Climate Change, pp. 30-40).

This matters because developed states’ mitigation strategies already imply large-scale reliance on carbon dioxide removal. Where a state relies on CDR as a substitute for feasible domestic mitigation, this increases the risk of overshoot or irretrievable carbon debt for three interrelated reasons. First, the global mitigation requirement remains unchanged. Where a state undertakes fewer domestic reductions, the corresponding reduction burden must be assumed by other states in the near term. Second, because rapid near-term emission reductions remain necessary, large-scale substitution through future removals is incompatible with a shrinking carbon budget. Like with mitigation abroad, there is only limited space for states to substitute short-term reductions with CDR. Third, maintaining the same global pathway would require the state to rely on higher levels of CDR, either before or after reaching net zero, to offset the resulting increase in its net emissions. Yet the effectiveness, potential, risks, costs and scale at which CDR can be deployed are still highly uncertain. Currently, the only widely practiced CDR is a limited set of mainly land-based methods – which are ironically declining because of the consequences of climate change.

What the Court Leaves Open

Ultimately, the Court’s procedural, “dialogical” approach, while preserving institutional balance, leaves key questions unresolved. These will likely reemerge if the State’s revised targets are challenged: with what standard and intensity of review should courts review pathways that substitute feasible domestic reductions with more uncertain alternatives? And how should courts interpret and evaluate the climate science on which such assessments depend, including uncertainties in modelling, scalability, and long-term effectiveness? More fundamentally, if 1.5°C is exceeded, courts may face questions relating to net-negative emissions, loss and damage, and responsibility for overshoot. Compensation claims alleging that states have exceeded their fair share would then expose a prior difficulty: how can courts assess responsibility for fair share exceedance, if they have not first specified the mitigation efforts required to remain within it? The judgment thus postpones questions that a shrinking carbon budget will make increasingly difficult to avoid.