Climate Justice Blog: Fair share climate litigation post-Klima – the French frontier

“As the window to limit global warming to 1.5ºC rapidly closes, States are running out of time to deliver their fair share of global mitigation action. The implication of the near-depleted remaining global carbon budget is that governments must act faster than ever before in terms of emissions mitigation, and compensate for emissions made in excess of the budget, in order for the temperature limit to be respected by the end of the century.” (Climate Litigation Network, “Fair Share and the Legal Obligations of States in an Era of Overshoot”, April 2026)

Paris, December 2015. 194 States signed up to the Paris Agreement, committing those States to using their best endeavours to limit global temperature rise to 1.5 degrees. 10 years on and an “overshoot” of that temperature goal looks increasingly likely. The cause – a significant “ambition gap”, the difference between the emissions reductions required to limit warming to 1.5 degrees and what States are pledging to achieve.

The ambition gap and its likely consequence of an overshoot of the 1.5-degree goal have combined with developments in climate litigation to spawn a category of climate case focussed on a country’s “fair share” of the remaining carbon budget. This litigation phenomenon owes much to the judgment of the European Court of Human Rights (“ECtHR”) in the Klimaseniorinnen case.  This case was the first instance of a country being found to have inadequate emissions reduction targets, a conclusion which relied on an analysis of the remaining Swiss carbon budget, which itself was calculated on the basis of an “equal per capita” allocation of the remaining 1.5-degree carbon budget. Coupled with the International Court of Justice’s Advisory Opinion (the “ICJAO”) on State obligations in respect of climate change in July 2025, and its emphasis on the principles of equity and of common but differentiated responsibilities and respective capabilities (CBDR-RC), climate litigators have picked up the baton and started to bring domestic challenges on “fair share” principles.

France is one country that provides a case in point of this new wave of “fair share” litigation. The rest of this article provides an overview of the French fair share case and provides insight into the shape this kind of case takes in practice.

Eating too much of the cake – the French fair share case

December 2025, and for many, the aftermath of a disappointing COP30 in Belém. In a timely move, the prominent French environmental NGO, Notre Affaire à Tous (“NAAT”), countered the ambient despair by filing a new type of climate case before France’s highest administrative court, the ‘Conseil d’État’. Referred to as the case for “la part juste”, the case argues that France is consistently failing to reduce its greenhouse gas emissions with sufficient speed and, therefore, to do its “fair share” to mitigate climate change. Or, as NAAT puts it in more visual terms, France is eating too large a share of the global carbon budget cake, leaving other countries with an unfairly small slice. Quintessentially French gourmandise applied to climate change.

The case builds on two previous judgments of French courts which found the actions of the French State to be lacking as regards climate mitigation, but which subsequent government decisions had purposefully gone against. NAAT’s core argument also derives considerable support from the KlimaSeniorinnen judgment and from the ICJAO.

The aim is as ambitious as it is clear: define France’s responsibilities for emissions reductions given its overall level of responsibility for the climate crisis. In essence, this is a case that seeks to take the principle of equity from its rather academic status in climate law and to operationalise it in climate litigation. If it succeeds, it could create a sizable ripple effect, facilitating the reliance in other cases around the globe on the same translation of the equity principle from legal theory to courtroom.

The case explored

The French fair share case highlights the contrast between the raising of the EU’s climate mitigation ambition from a 40% to a 55% reduction by 2030, defined in the “Fit for 55” package in 2021, with the sluggishness of France’s domestic action. France’s real-world progress shows no such increase in ambition nor real-world emissions cuts. France’s emissions in 2024 dropped by only 1.8%. In 2025, the decrease was even less at just 1.5%. Not only is the country’s annual 5% emissions reduction being missed but progress is going backwards. The result – France’s emissions are off the mapped trajectory for limiting the global temperature increase to 1.5 degrees, as required by Article 2(1) of the Paris Agreement (the long-term temperature goal, or LTTG). This misalignment is even more crucial in view of the International Court of Justice’s conclusion in the ICJAO that 1.5 degrees is indeed “the parties’ agreed primary temperature goal for limiting the global average temperature increase under the Paris Agreement”.

The principles of equity and CBDR-RC in practice

The crucial difference between the French fair share case and previous climate litigation is that NAAT relies on a much broader assessment of France’s contribution to the climate crisis. In accordance with the principle of common but differentiated responsibilities, historic emissions are factored into the assessment of France’s level of responsibility. Different start dates exist for the assessment of historic responsibility for greenhouse gas (GHG) emissions: 1750, 1950 or 1990. For this case, no doubt to maximise the chances of a successful outcome, NAAT has chosen the most favourable date for France – 1990. France’s imported emissions are also included, and importantly so.

This volume of extraterritorial GHGs accounts for around half of the country’s total carbon footprint, similar to those of China. Unlike previous litigation, the French fair share case also takes into account France’s net, rather than its gross, emissions, and its level of economic development. The latter shapes the country’s ability to take mitigation actions which, NAAT argues, should include reducing its imported emissions, contributing more generously to international climate finance initiatives for poorer countries and more effective regulation of high-emitting French companies, including multinationals.

The science behind “fair share”

The case rests heavily on an assessment of France’s “fair share” of the global carbon budget, an assessment performed for NAAT by a group of three European scientists who had previously produced a similar analysis for Italy. Their report and its conclusions lie very much at the heart of the legal action, and the case’s chances of success will significantly depend on the court’s perception of its credibility and accuracy.

The request for the report follows on from the conclusion of the European Scientific Advisory Board on Climate Change (“ESABCC”) in June 2023, that the EU has already exceeded its carbon budget for limiting warming to 1.5 degrees. The report follows the same methodology as ESABCC in order to determine, to at least a 50% probability, France’s fair share of the remaining global carbon budget in order for the 1.5-degree temperature goal to be met, using four different interpretations of “equity”.

The findings of the report are deeply concerning. In all of the four equity scenarios (1. equal share per person, 2. historic responsibility, 3. economic capacity and 4. historic responsibility and economic capacity combined), France has an insufficient amount of the carbon budget to continue on its current emissions path, even for the next few years. As of 2023, the best-case scenario of France’s fair share of the remaining 1.5-degree carbon budget was estimated to be 1.70 gigatons of CO2. The worst-case scenario was minus 8.06 gigatons. The inevitable conclusion – in 2026, on any of the four equity scenarios, France has already exceeded its fair share of the 1.5-degree carbon budget. All further emissions are either depriving other States of their fair share of the emissions budget or pushing the world into overshoot. The latter seems more likely.

Remedies

NAAT’s pleadings ask the court to take several measures against the French State. First, it asks the Court to annul the French government’s implicit decision not to set down a clear, decisive emissions reduction trajectory for France’s territorial emissions that is aligned with the best available science and with France’s international, European and national obligations as set down in paragraphs 544 onwards of the Klimaseniorinnen decision. The “implicit decision” arose from a failure by the French government to respond to a request in the material terms above that was made of it by NAAT in September 2024. Through the annulment request, NAAT asks the court to order the French state to take those same measures as in the request, and specifically to ensure that the trajectory is aligned with the 1.5-degree goal, that it takes account of weakening carbon sinks and that it reflects the CBDR-RC principle. Partly to this end, NAAT states that intermediate targets for 2030, 2040 and 2050 should be required to be set by the government as part of the trajectory.

The claimants further ask the court to take a range of other measures:

• Mandate the government to produce a coherent trajectory for the reduction of France’s extraterritorial emissions in line with the same international, European and domestic obligations.
• Take whatever measures it can to ensure that France implements the above requirements, in particular the trajectory, and specifically in relation to the land use, land use change and forestry sector (LULUCF). It is unclear why the LULUCF sector has been singled out for special mention, although it is conceivably in recognition of France’s rapid loss of its carbon sink.
• Withdraw France’s latest National Integrated Climate and Energy Plan (“NECP”), as sent to the European Commission, and provide a new one in its place. NECPs are a requirement of all EU Member States under Regulation 2018/1999 (the “Governance Regulation”). They must set out how the EU Member State in question intends to meet the EU’s climate and renewable energy targets through policies, targets and other measures over a 10-year period. They are, therefore, a vital tool for meeting the 1.5-degree temperature goal.

Interestingly, the claimants also seek the imposition of a hefty financial penalty if the government does not comply, amounting to damages of 10 million euros per semester of delay.

Conclusion

The French fair share case is not the first that seeks to apply fair share arguments to a challenge to national climate change action. In March 2021, the German case of Neuberger et al. v Germany saw the Federal Constitutional Court agree with some of the Claimants’ arguments challenging the Federal Climate Protection Act, and strike down parts of the Act, on the basis that the emissions reduction targets therein placed an unfair burden on future generations. The court accepted the argument that the German legislature should take a carbon budget approach to limiting warming to the LTTG. On the basis of an assessment of Germany’s remaining carbon budget, it found that the Act’s emissions reduction targets breached fundamental rights by offloading an unfair share of the mitigation burden onto future generations.

In 2024, in the case of Do-Hyum Kim, the Supreme Court of South Korea found that “States must determine and implement climate policies based on their fair share of global mitigation efforts”. With respect to the ambition of South Korea’s own climate policies, the court held that the Government had violated the right to a healthy environment by failing to set emissions reduction targets for the 2031–2049 period. Similarly to the Neuberger case, the court considered that this meant that young and future generations would be left with a disproportionate and unfair mitigation burden.

What is novel about the French fair share case is that it is the first time that a national court is being asked to compel a government to set out a pathway, based on the best available science, to limit warming to 1.5 degrees. The case stands out for incorporating historic responsibility into an assessment of a state’s legal responsibilities for mitigating climate change. It is also the first time a court is being asked to order a government to include exterritorial emissions within an emissions reduction trajectory, and to apply the CBDR-RC principle. The case marks a clear progression from the German and South Korean precedents, bolstered by the Klimaseniorinnen judgment and the ICJAO.

Whether or not the case succeeds, it is likely to inspire other fair share litigation in the coming years and to push the boundaries of climate litigation. The acceptance by the ECtHR and by several national courts of the carbon budget approach to assessing the adequacy of state climate mitigation action has provided an essential component for such challenges to be brought, while the existing domestic fair share litigation has shown a judicial willingness to accede to such arguments. With a study last year finding a 50% probability that the global carbon budget for 1.5 degrees could be depleted as early as the end of 2028 (Forster et al, 2025), climate litigators across Europe and beyond will undoubtedly be keeping fair share arguments at the forefront of their strategic thinking for the foreseeable future.

As to the effectiveness of a “fair share” approach, the fact that the arguments have already gained traction in at least three judicial fora makes it one of the most successful approaches in climate litigation to date. While it looks very unlikely to succeed in limiting global temperature rise to 1.5 degrees, fair share argumentation looks to have a vital role to play in limiting the 1.5-degree overshoot as far as possible.