As temperatures continue to rise at alarming rates, it is undeniable that current climate policies are not enough to meet the 1.5°C temperature limit of the Paris Agreement. According to the United Nations Environment Programme, global warming is currently on track to reach 2.8°C above preindustrial levels by 2100. However, if governments fully implement their Nationally Determined Contributions (NDCs), this figure would fall to 2.3°C to 2.5°C. Fulfilling existing climate commitments is thus an essential component of limiting temperature rise and preventing further dangerous climate change.
To that end, individuals and groups around the world have called on domestic, regional, and international courts to hold governments accountable when they fall short of their climate pledges. In these “implementation” cases, courts have clarified that governments must do more than just define targets. Rather, they must also establish clear and actionable plans for achieving them, monitor their progress, and take timely corrective action to address any implementation shortcomings. Recent decisions – including the advisory opinions on climate change from the International Court of Justice (ICJ) (2025) and Inter-American Court of Human Rights (IACtHR) (2025), as well as Verein KlimaSeniorinnen Schweiz and Others v. Switzerland (2024) at the European Court of Human Rights (ECtHR) – have solidified these requirements, building upon a long line of domestic cases stretching across jurisdictions from Leghari v. Federation of Pakistan (2015) to Notre Affaire à Tous et al. v. France (2021) and beyond.
This two-part post will examine the broad scope and relevance of implementation litigation. The first entry here will touch on some of the most significant jurisprudence from these judgments to show how courts across all levels have developed clear and substantive legal standards for assessing governments’ implementation of their climate commitments. The second post will look at a new generation of cases that are emerging alongside a range of increasingly complex legal and political dynamics. Taken together, these insights will offer a glimpse into how implementation litigation is evolving to further strengthen accountability and help close the gap between promises and action amidst advancing challenges to climate progress.
International and regional jurisprudence solidifying governments’ substantive implementation duties
One of the many significant conclusions from the ICJ’s landmark advisory opinion on climate change concerns its findings on NDCs. The ICJ explained that States not only have limited discretion when it comes to setting the substantive content of their NDCs, but that fulfilling those NDCs is not purely voluntary or aspirational, as some States have previously argued. Instead, according to the ICJ, all States have an individual substantive obligation to “pursue domestic mitigation measures” with the aim of implementing their NDCs (paras. 250-51) and judged against a stringent standard of due diligence (para. 254). To that end, States’ implementation measures must be “reasonably capable” of achieving climate commitments, and anything short of “best efforts” to do so will fall short of their obligations (para. 253). As the ICJ indicated, this requires a significant government response with an eye towards achieving NDCs, such as the establishment of a national system complete with legislation, administrative procedures, enforcement mechanisms, and vigilant oversight of its effectiveness (para. 253).
At the regional level, the approach of the IACtHR towards implementation is very much in alignment with the ICJ. According to the IACtHR in its advisory opinion on climate change, States must define strategies and adopt binding measures to achieve their mitigation targets under an enhanced standard of due diligence (para. 335). These measures must be “realistically implementable” and, inter alia, take into account high emitting sectors; prioritize actions that deliver prompt and lasting results; reflect maximum use of available resources; consider best available science; and include goals, timelines, and rules for public and private stakeholders (para. 336).
The ECtHR in KlimaSeniorinnen held that the effective protection of human rights against climate change impacts requires States to set out intermediate targets capable of meeting long-term net-zero goals; provide evidence that they have complied (or are complying) with those targets; update targets based on due diligence and best available science; and act in good time and consistently when devising and implementing climate measures (para 550(b)-(e)). In finding a violation of Article 8 of the European Convention on Human Rights (ECHR), the Court noted that Switzerland failed to achieve its 2020 target, and did not put in place “concrete measures” to achieve intermediate and long-term climate targets (paras. 559, 564-65).
Read together, international judicial practice shows that States are under a duty to put in place and carry out measures that are reasonably capable of achieving their climate targets, in accordance with an elevated standard of due diligence.
Domestic outcomes as implementation litigation building blocks
The international and regional jurisprudence above builds on the seminal implementation litigation that has taken place in domestic courts for over a decade – and which continues to break new ground in the field.
Courts in the Global South, in particular, have taken a bold approach to remedying implementation shortcomings, particularly where government inaction persists. In Leghari – one of the earliest implementation cases – the Lahore High Court explained that Pakistan’s “delay and lethargy” in implementing its existing climate framework violated the fundamental rights of its citizens. In response, the court created a supervisory Climate Change Commission to assist the country’s implementation efforts. Three years later, a supplementary report revealed that 66% of identified priority climate actions had been implemented.
In another early case, Shrestha v. Office of the Prime Minister et al. (2018), Nepal’s Supreme Court required the government to enact a new climate law “as soon as possible” to fulfil its existing mitigation and adaptation commitments (para. 33), which the country subsequently did by passing the Environment Protection Act 2019 and updating its national climate policy. In Latin America, Brazil’s Supreme Court declared in PSB et al. v. Brazil (on Climate Fund) (2022) that the government had a constitutional duty to operationalize a climate change fund to help carry out its climate obligations under the Paris Agreement and domestic law. This was subsequently carried out and reshaped by the Lula administration.
In Europe, courts have played a leading role in holding governments accountable for substantiating their climate plans and meeting their emissions targets. In Notre Affaire à Tous et al v. France, the Administrative Court of Paris held that France had failed to meet its 2015–18 carbon budget, resulting in an unlawful “surplus” of greenhouse gas (GHG) emissions. The Court acknowledged that this had partially contributed to ecological damage, thus triggering liability under the French Civil Code, and ordered the government to adopt “all measures” necessary to address this surplus.
In Friends of the Irish Environment v. Ireland (FIE) (2020), the Irish Supreme Court held that the government’s climate plan failed to articulate with sufficient specificity how it would achieve its long-term decarbonization goals. Accordingly, the Court quashed it and ordered the government to address the deficiencies in a new plan. Similarly, in DUH v. Germany [re insufficient climate action programme], the Higher Administrative Court of Berlin-Brandenburg concluded in 2024 that Germany’s climate action programme covering the transport, energy, industrial, buildings, and agriculture sectors was insufficient in light of the country’s 2030 and 2045 emission reduction targets, and ordered the government to revise it. In January 2026, the Federal Administrative Court upheld the judgment, finding that the 2023 program would not meet the 65% mitigation target set for 2030, and failed to show how individual sectors would meet annual emission limits under Germany’s climate law.
Although national governments are responsible for implementing their countrywide emissions targets, the role of subnational authorities – such as federated states, regions, and municipalities – cannot be overlooked. These entities are central to the practical implementation of national plans and can stall overall progress when they fail to act. The history of successful cases targeting subnational inaction in countries such as Germany (Deutsche Umwelthilfe v Baden-Württemberg) (2022), Australia (Bushfire Survivors for Climate Action Incorporated v. Environmental Protection Authority) (2021), and India (Mahendra Pandey v. Union of India (2019); Gaurav Bansal v. Union of India (2015)) shows that courts around the world are willing to scrutinize implementation responsibilities at a granular level and, where relevant, require subnational governments to adopt and implement their own climate plans.
Finally, many domestic courts have already applied the international legal framework described above to hold governments accountable for implementing their climate commitments. This has created a mutually reinforcing dynamic in which domestic courts have provided crucial building blocks for the development of international jurisprudence, with subsequent domestic cases then relying upon and furthering that jurisprudence. Several of those instances, from courts in countries such as Brazil, Ireland, and the Netherlands, will be examined in the second post in this series.
Conclusion
As this post has shown, a growing body of jurisprudence from international, regional, and domestic courts has cemented the understanding that governments cannot discharge their legal obligations merely by setting targets and adopting plans. Collectively, these decisions have established that governments have a legal duty to pursue a credible, transparent, and timely implementation of their commitments. As a result, the progress governments make in operationalizing and ultimately achieving their goals is subject to judicial scrutiny.
Although courts have firmly clarified these obligations across all levels, a new wave of cases is emerging alongside increasingly complex legal and political dynamics, including efforts to dilute climate laws, reverse regulatory measures, and undermine the institutional frameworks supporting climate action. The second part of this blog will examine these trends, illuminating how implementation cases have a key role to play in holding governments accountable in the face of rapidly shifting circumstances.