On 10 and 11 November2025, the Hellenic Council of State and ACA-Europe organised a seminar entitled “Climate change / Climate crisis - Overtourism”. This was the first seminar held under the Hellenic Presidency of ACA-Europe. The seminar brought together more than 70 participants: representatives of the Councils of State and supreme administrative courts of ACA-Europe Member States, as well as States with observer or guest status within the Association.

On 10 and 11 November 2025, in Athens, the Hellenic Council of State, in collaboration with ACA-Europe, organised a seminar on climate change and overtourism. This was the first seminar held under the Hellenic Presidency of ACA-Europe. The seminar brought together more than 70 participants: representatives of the Councils of State and supreme administrative courts of ACA-Europe Member States, as well as States with observer or guest status within the Association.

As its title suggests, the seminar focused primarily on the legal challenges posed by climate change – or rather the climate crisis – and the phenomenon of overtourism, as well as the role of administrative justice in responding to these contemporary issues. The two issues have much in common – consider, for example, that the tourism sector alone accounts for nearly 8% of global greenhouse gas emissions. And yet, they do not seem to share the same level of severity. Climate change has the potential to be threatening to our planet and even destructive to humanity itself. As the International Court of Justice stated in its recent advisory opinion of 23 July 2025 on the obligations of States in relation to climate change, the questions raised concern an existential problem of global significance that threatens all forms of life and the very health of our planet. Overtourism, although it can cause serious problems, may not be as threatening as it seems, at least for now.

The seminar began with welcoming speeches by the President of the Hellenic Council of State, Michail Pikramenos, who thanked the participants for their responses to the questionnaire, demonstrating remarkable commitment, and by the former President of the Hellenic Republic and Honorary President of the Council of State, Katerina Sakellaropoulou.

The responses to the questionnaire contributed significantly to the general report, which, like the questionnaire, was divided into two parts that were presented and discussed during two corresponding sessions. In addition to reports on more specific topics (see below), several national contributions (Portugal, the Czech Republic, Estonia and Serbia during the first session, and the Netherlands, Lithuania and Spain during the second) also contributed to the discussion on the topics covered by the seminar.

First session: climate change

The general report was presented by Olga Papadopoulou, Honorary Councillor of State, and Vassilis Androulakis, Councillor of State:

According to the rapporteurs, with regard to the international dimension of the problem, it is important to bear in mind the regulatory framework, whose three main pillars are the treaties on climate change, namely the United Nations Framework Convention [Rio de Janeiro, 1992], the 1997 Kyoto Protocol and the Paris Agreement, adopted in 2015.

European Union law forms the common basis for national legislation in the EU Member States, but also in candidate countries and in the United Kingdom. In the ‘European Green Deal’, presented in December 2019, the Commission reiterated its commitment ‘to tackling climate and environmental-related challenges’ and announced a ‘new growth strategy’ in response to these challenges. Two regulations, mandatory and directly applicable in Member States, Regulation (EU) 2021/1119, known as the ‘European Climate Law’, and Regulation (EU) 2018/1999 on the governance of the Energy Union and climate action, which establishes a mechanism for ensuring that the Union’s objectives are achieved, form the core of the legal arsenal.

Last but not least, at international level, reference should be made to the European Convention on Human Rights, and in particular Article 8, as well as Articles 2 and 6.

With regard to national legislation, it can be seen that in most countries there are rules or principles at constitutional level for the protection of the environment, health and young people or other groups of the population. Constitutional rules that refer explicitly to climate change are rare, with the notable exceptions of Luxembourg and Finland. On the other hand, several Constitutions contain explicit references to solidarity between generations and/or the rights of future generations and vulnerable groups.

As mentioned above, international law and European Union law form the basis for national climate legislation. These laws establish the legal framework for managing issues related to climate change.

With regard to the application of the regulatory framework, the courts in most European countries have not yet been asked to rule on disputes directly involving climate change issues, unlike most disputes brought before administrative courts, which generally concern environmental law.

The administrative acts that are being challenged are those of the second type of litigation and concern Environmental Impact Assessments, Strategic Environmental Assessments, the granting of permits for the construction of power plants, and land use plans. One example is the shale oil plant in Auvere reported by Estonia (Case No 3-20-771), where an oil production licence was revoked due to its incompatibility with the Paris Agreement. Other examples include permits for energy infrastructure, such as wind turbines, and urban planning decisions.

In Greece, as Dimitrios Pyrgakis, Master of Petitions at the Council of State, has pointed out in several cases concerning energy market regulation, the renewable energy sources regime, the fuel improvement regime, etc., the importance of measures to tackle climate change is taken into account by the judge, both in interpreting the applicable legal regime and in reviewing the legality and, in particular, the proportionality of the decision challenged in court.

The first type of dispute most often concerns cases where the inaction and failure of the Administration is called into question.

France referenced two cases relating to global warming. Firstly, the Commune de Grande-Synthe (Municipality of Grande-Synthe) ruling of the Council of State of 10 May 2023. The Council of State instructed the Government to take all necessary measures before 30 June 2024 to achieve the target of reducing greenhouse gas emissions by 40% in 2030 compared with 1990 levels, in order to comply with the Paris Agreement and the European commitments adopted by French legislators. Very recently (24 October 2025), the Council of State closed the case, having considered that the measures taken by the French government were sufficient.

Secondly, France referenced the Affaire du siècle (Case of the Century): In 2021, the Paris Administrative Court issued a ruling ordering the government to take ‘all necessary measures’ to ‘repair the ecological damage’ by 31 December 2022 at the latest. It considered that the reduction in greenhouse gas emissions observed in 2020, although mainly due to the COVID-19 pandemic and not to government action, had to be taken into account when assessing the damage.

With regard to the Netherlands, in the Urgenda case (judgment of the Dutch Supreme Civil Court of 20 December 2019), the Court ruled that the State was obliged to reduce these emissions (by 25% by 2020). This obligation stems from Articles 2 and 8 of the European Convention on Human Rights (right to life and respect for private and family life) and cannot be disregarded on the basis of political considerations.

Italian case-law appears to be more restrictive in the Last Judgment (Giudizio Universale) case – an evocative title reminiscent of Michelangelo’s famous fresco. In 2024, the Court of First Instance in Rome dismissed the appeal as inadmissible. The applicants sought recognition of the State’s obligation to take all necessary measures to reduce national carbon dioxide equivalent emissions by 92% by 2030 compared with 1990 levels, or to adopt another measure to be determined during the proceedings. According to the court, the issues raised were matters of ‘political orientation’, involving the determination of the broad outlines of state policy on the sensitive and complex issue of climate change, and therefore the applicants did not have a protected right or interest on which to base their claim.

With regard to international law, the recent opinion of the International Court of Justice (23 July 2025) presented by Ilias Plakokefalos, Associate Professor of International Law at the National and Kapodistrian University of Athens, is very important. The Court clarified the obligations of States in relation to climate change and specified that protecting the climate is a legal obligation, potentially influencing international legislation and policies, even without binding force. By clarifying the scope of existing rules, the Court sent a clear message: protecting the climate is a legal obligation, not just a political choice.

Two advisory opinions should also be mentioned: that of the International Tribunal for the Law of the Sea (21 May 2024) and that of the Inter-American Court of Human Rights (3 July 2025). These opinions confirm that States have stringent obligations under human rights law and international law more generally to reduce greenhouse gas emissions. The Inter-American Court recognises the human right to a stable and healthy climate, which is part of the right to a healthy environment. States have a positive obligation to prevent, mitigate and adapt to climate change. Enhanced protective measures must be put in place to protect vulnerable populations (indigenous peoples, children, rural communities and communities of African descent).

Where the European dimension is concerned, the first thing to note is the climate-related judgment of the European Court of Human Rights (ECtHR) in Verein KlimaSeniorinnen Schweiz and Others v. Switzerland (4 September 2024). As explained by Linos-Alexandros Sicilianos, Professor of International Law at the National and Kapodistrian University of Athens and former President of the ECtHR, in this case the Court found two violations of the Convention – one on the merits (Article 8 in light of Article 2 and international law) and the other on procedure (Article 6). What is interesting is that the case did not concern a form of pollution linked to a particular human activity, but a global phenomenon, climate change. The Court incorporated this issue into the scope of the Convention, despite the fact that the Convention does not recognise the right to a healthy environment. Its findings under Article 8 confirm that States have positive obligations under human rights law to effectively regulate and reduce greenhouse gas emissions, in line with the goal of achieving global carbon neutrality within the next three decades.

The very recent judgment (handed down on 28 October 2025) in Greenpeace Nordic and Others v. Norway concerns the obligation to effectively protect individuals from the adverse effects of climate change on their lives, health, well-being and quality of life in the context of oil exploration activities prior to extraction. The ECtHR concluded that there had been no infringement of Article 8.

Finally, Panagiotis Vogiatzis, Legal Secretary at the Court of Justice of the EU, demonstrated that, even though there is no ‘right to a stable climate’ in the case-law of the Court of Justice of the European Union (CJEU), it has resulted in a rigorous methodology that allows Member States to be monitored through precaution, scientific rigour, access to justice, consistent planning and enforcement. Furthermore, by comparing the cases concerning the Ilva steelworks before the CJEU and the ECtHR, he highlighted the interaction between the two courts, whose methodologies differ but whose requirements and approaches converge.

According to Dimitrios Skaltsounis, Honorary President of the Council of State, whose conclusions from the seminar served as the basis for this summary, the analysis of the legislation and case-law cited, both international and national, the opinions issued by international courts, and the ensuing dialogue, allow several useful conclusions to be drawn.

Firstly, as Linos-Alexandros Sicilianos noted, climate change should not normally be a matter for the courts – it should be addressed through legislative measures or measures taken by the executive branch, in the context of international agreements. However, faced with the inadequacy of the measures taken by the competent authorities, the national courts have adopted important decisions and rulings: Supreme Court of the Netherlands, French Constitutional Council, German Constitutional Court, Council of State, etc. This case-law has created momentum at international level (judgments and decisions of the ECtHR, opinions of international courts).

Secondly, judges issue rulings, decisions or opinions on the issue of climate change and shape case-law, sometimes boldly, on both procedure and merits. As such, we can see a relaxation of the rules governing the interest in taking action. By way of example, the ECtHR recognises a legitimate interest on the part of non-governmental organisations, but not on the part of individuals (Verein KlimaSeniorinnen judgment, cited above), and does not recognise an interest in cross-border action (judgment in Duarte Agostinho and Others v. Portugal and 32 other States, 9 April 2024). However, on this last point, the Oberlandesgericht Hamm (Higher Regional Court of Hamm) (Lliuya v. RWE AG, 30 November 2017) recognised the legitimate interest of a Peruvian farmer who had brought an action against a large energy company operating coal-fired power stations in Germany. It should also be noted that, in most national legal systems, there is no actio popularis (except in Portugal). Finally, it must be borne in mind that the instruments available to judges, both in terms of merits and procedure, at national and international level, are not always the most appropriate, and that there are inherent difficulties in climate change litigation. For example, although there is a tendency towards a lower standard of proof, it is difficult, in the context of climate change, a global phenomenon par excellence, to establish proof of the harmful consequences resulting from the actions or omissions of the Administration.

Thirdly, the task facing judges is particularly difficult. They must strike the necessary balance in order to reconcile legitimate interests, protected by norms of the same level (e.g. the Constitution), but which are nevertheless antagonistic and require application in a given case. As Theodora Ziamou, Master of Petitions at the Hellenic Council of State, pointed out, taking into account climate change and its effects in all contexts – permits, economic development, energy efficiency, renewable energies, forest protection, construction, urban planning, vulnerable populations, refugees, etc. – national courts will be required to rethink the weight they give to climate protection when balancing it against other rights, interests and administrative objectives protected by the Constitution. To accomplish this task, judges are to a large extent forced to rely on technical assessments, which in principle cannot be verified, and on data provided mainly by a single party: the State. Of course, they can always order an expert opinion or request the assistance of an amicus curiae (example contributed by the Czech Republic). Sweden could also provide an interesting idea, which is the mixed composition of courts in environmental cases, with ordinary judges and experts.

Fourthly, judicial review in relation to climate change affects many aspects of economic policy and development (as in the Italian Giudizio Universale decision, cited above), which could raise sensitive issues, particularly at the enforcement stage. We can also mention here the Verein KlimaSeniorinnen judgment (cited above) where, despite an initial reaction from the Swiss State, an agreement was reached between the latter and the Committee of Ministers, which found (18 September 2025) that the measures taken by the former were sufficient to be considered in compliance with the judgment; at the same time, the Committee invited Switzerland to submit another report for evaluation in 2026.

These findings should not lead to a pessimistic view, nor to the assumption that judicial texts have no more than a declaratory value with regard to climate change. Rather, they should encourage a realistic approach to the limits of judicial review. This form of review is progressing both in scope and depth, albeit in a non-linear manner and sometimes with setbacks. Despite its inherent difficulties, such review is effective and feasible. Furthermore, it acts as a means of pressure and as an incentive for legislators and the executive branch to take the necessary steps to mitigate the consequences of climate change.

As President Skaltsounis noted in his closing remarks at the end of this first session, it should be emphasised that efforts to reverse climate change are likely to resemble a Sisyphean task as long as they remain confined to European countries alone. Admittedly, the approach adopted by certain European jurisdictions demonstrates the increasingly international nature of case-law concerning the liability of energy producers with regard to issues related to the greenhouse effect. In this regard, the ruling of the Higher Regional Court of Hamm (Lliuya v. RWE AG, 30 November 2017, cited above) is emblematic. However, the countries of Asia, Africa and America, which account for the majority of the world's ever-growing population and which have set other priorities, foremost among which is the immediate improvement of their citizens' standard of living, naturally do not share the same concern about the climate crisis. And yet it is precisely these countries that bear much of the responsibility for the greenhouse effect. Consequently, global cooperation in this area (which was the subject of the advisory opinion of the International Court of Justice, mentioned above) is not only a desirable objective: it is an absolute necessity and a matter of urgency.

Second session: overtourism

Here too, the general report was presented by Councillor Papadopoulou.

According to a commonly accepted definition, overtourism ‘describes the situation in which the impact of tourism, at certain times and in certain places, exceeds physical, ecological, social, economic, psychological and/or political capacity thresholds’, or, in other words, corresponds to the situation where ‘too many people are in the same places at the same time’.

By way of example, as pointed out by Marina Perelli, Councillor of State at the Italian Council of State, Santorini recently welcomed up to 11,000 tourists in a single day, compared with a local population of 15,000, while Venice sees more than 100,000 motorised boats passing through every day, with harmful effects on the urban environment and the quality of life of the residents who remain there.

Unlike climate change, overtourism is a relatively recent phenomenon. It does not affect all countries – or even all regions within the same country – and although it is a significant issue, it does not pose any problems for the future of the planet, at least not directly. For all these reasons, the approach to the problem of overtourism has so far been rather fragmented. There is a lack of global or European legislation directly addressing this issue, while the measures proposed and adopted at national level are mostly small-scale attempts to respond to immediate and acute problems faced by local communities (the prime example being short-term rentals).

As Olga Papadopoulou has noted, there is no international legal instrument or European Union legislation that directly and specifically addresses the issue of overtourism and its effects. However, as highlighted in the national reports, various principles and guidelines are set out in binding and non-binding texts; these guidelines have often been useful in developing national laws and policies aimed at managing tourism. Nevertheless, the diversity of standards required to achieve this is still preventing any successful attempts at rationalisation.

It should also be noted that mass tourism, which is not very different from overtourism, should not automatically be considered a negative phenomenon. It represents the democratisation of tourism. Take Venice, for example: between the Grand Tour, reserved for the elites of the eighteenth and nineteenth centuries, and the tourist invasion of the twentieth and twenty-first centuries, the ideal would be a fair balance, seeking to maximise profits while minimising the undesirable effects of tourism.

The issue of overtourism is particularly complex, as it requires balancing conflicting interests. In the case of overtourism, the interests of local communities conflict with those of investors. However, it is important to emphasise the following point: due to short-term rentals, roles become blurred, and residents themselves often become contributors to overtourism through digital platforms. This results in a deterioration in residents’ quality of life and a loss of authenticity in the most visited historic centres.

Marina Perelli also demonstrated the need for a new ordering of priorities, namely the conservation of tourism resources, the protection of residents and local businesses, and the management of territorial effects. Among the regulatory tools being considered to limit the effects of overtourism are the introduction of licences for tourist rentals, taxation of second homes, regulation of access to highly frequented sites, and urban planning aimed at preserving the balance between residential and commercial areas.

In most countries, administrative disputes, particularly those concerning environmental and planning law, are the main means of bringing disputes before the national courts. The case-law of the Netherlands is of particular interest. It shows how appropriate measures (such as banning the opening of new tourist shops in the city centre) can reduce the pressure of overtourism on a specific location (in this case Amsterdam) and channel tourist flows to other, lesser-known places of interest (decision of 19 December 2018). However, the contested measures must have a direct causal link with the deterioration in the quality of urban life. Furthermore, it should be noted that certain nuisances are inherent to living in a bustling city centre such as Amsterdam. Consequently, a decision by Amsterdam City Council to limit the issuance of operating licences for passenger boats was overturned on the grounds of insufficient justification (decision of 25 September 2024).

Italian case-law has also addressed the issue of overtourism in a decisive manner. The Italian Council of State has approved measures to limit the opening of new restaurants in historic centres such as Amalfi, in order to preserve cultural heritage and urban quality of life. The contributions from Lithuania and Spain also provided us with many interesting ideas, both in terms of initiatives by the authorities and case-law. It should also be noted that very recently, the Hellenic Council of State (judgments 1900-1907/2025) addressed for the first time the issue of short-term rentals in the historic Pláka district of Athens, as well as the legality of tourist accommodation in an area where only residential use is permitted (the final ruling has, however, been postponed).

As President Skaltsounis noted in his closing remarks at the end of this second session, it is interesting to observe how we have moved from the democratisation of tourism to the search for the principles of sustainable tourism, a whole new avenue to explore. In relation to this issue, administrative justice plays a pioneering role in redefining the public interest and setting limits on private initiative, in other words, it responds to new challenges through its traditional role.