How the Court of Justice of the European Union deals with scientific knowledge

and what this means for Member State court practice

by Christoph Sobotta*


When courts need to engage with scientific knowledge, in particular in the area of environmental law, they will often deal with cases involving complex appreciations. The Court of Justice of the European Union addresses this challenge with considerable “judicial self-restraint” and this practice defines a minimum standard that Member State Courts need to respect when working with EU law.

Complex Assessments and Balancing

The complexity of assessments required for the application of environmental law results from scientific uncertainty in relation to many questions that authorities need to answer in this context. This uncertainty may be an expression of insufficient knowledge about the effects of certain actions, but it can also be a consequence of the complexity of the affected environment.[1] Though we can eliminate the first type of uncertainty with additional research, it may not be possible to overcome the second type. Complete knowledge of complex systems can rarely be acquired and therefore such systems often react unpredictably to inputs.

In the field of the environment, EU regulatory measures, such as the ban of the additive methylcyclopentadienyl manganese tricarbonyl (MMT) in automobile fuels,[2] can serve as examples. When the EU introduced the ban, Parliament and Council considered that the use of MMT was very damaging to the environment. Conversely, this ban had not been in the Commission proposal because it considered the scientific evidence to be insufficient. Moreover, several years later, before the Court, the producer still argued that there was no proof of damage without being substantially contradicted by the institutions. Effectively, there was some evidence pointing towards harm, but not enough to establish this harm with sufficient certainty.[3]

The MMT ban also illustrates another element of environmental decision-making, namely the balancing of competing interests. After arriving at the conclusion that the additive posed a risk to the environment, the legislator needed to decide whether the risk justified restricting the economic freedom of additive producers and the freedom of choice of consumers. In particular, it was argued that the use of the additive was necessary to prevent harm to engines. Therefore, the legislator needed to appreciate whether less restrictive measures could be adopted and whether the advantages of a ban would outweigh possible negative consequences. It should be noted that this final balancing exercise required a comparison between two sets of uncertain harm – on the one hand uncertain harm to the environment and on the other hand highly likely economic harm to the producer, but also uncertain harm to the consumer.

Judicial Review of Complex Assessments and Balancing

Courts need to address complex assessments and balancing, such as the MMT ban. Under the rule of law, effective judicial protection needs to be available and this right is enshrined in art 47 of the EU Charter of Fundament Rights. For environmental issues art 9 of the Aarhus Convention highlights this guarantee. This protection cannot exclude decisions taken in the light of scientific uncertainty and/or difficult balancing exercises. Nevertheless, judicial scrutiny of such decisions is a sensitive matter. Should courts apply very strict standards or act with restraint? To put it more practically against the backdrop of our example: How should courts verify whether the MMT ban was justified?

Procedural Autonomy of Member States

The principle of procedural autonomy is the starting point for any debate of this issue with regard to the review of the application of EU law within the Member State legal systems. In the absence of detailed EU rules governing judicial review of decisions implementing EU environmental law, it is generally for the domestic legal system of each Member State to determine those requirements. However the requirements cannot be less favourable than those governing similar domestic situations (principle of equivalence) and that they may not render impossible in practice or excessively difficult the exercise of rights conferred by the EU legal order (principle of effectiveness).[4]

It is conceivable that, in exercising procedural autonomy, Member States will grant their courts very far-reaching powers of review. On the far end of this spectrum, courts could be authorised to re-evaluate the scientific assumptions supporting a decision, examine additional facts or scientific theories or rebalance the competing interests, thereby substituting themselves for the administrative authorities. In such a system, courts could modify or replace the decisions they review. In case of the MMT ban, we could imagine that courts annul it if they are not convinced that it is justified or they could allow MMT for some use cases. It appears that in some areas the Swedish[5] and Finnish[6] legal system go a long way in this direction by employing expert judges and German courts often examine the technical assessment of the administration very intensively by hearing independent experts they select.[7] The practice in the Netherlands – although similar to Germany in that courts make extensive use of experts in environmental cases – goes a step further as the judiciary has its own independent foundation (STAB) of environmental experts at its disposal.[8] From the perspective of EU law, there can, in principle, be no objection to such review if it satisfies certain requirements, such as having an adequate scientific basis and complying with procedural minimum requirements resulting from fundamental principles of EU law.[9] Nevertheless, other legal systems apply more limited standards of judicial review.[10]

Minimum requirements for judicial review resulting EU law

The review criteria applied by the EU Courts in examining complex assessments by the EU institutions, for example the MMT ban, allow identifying the minimum level of scrutiny, which the review of the application of EU law by the Member State courts must achieve. While EU law, in particular art 19 TEU and art 47 of the Charter, requires that the Member States establish a procedure for effective judicial review of national decisions applying EU law,[11] this review (in principle) need not be more extensive than that carried out by EU courts in similar cases.[12]

However, before we look into this standard, a distinction is necessary between the review of Member State action by the Court of Justice and the review of EU measures. The Court reviews Member State action under art 258 ff. TFEU. In most cases, the Commission initiates such an action, but sometimes other Member States employ it, too. The object is a finding that a Member State has infringed EU law. In these proceedings, the applicant bears the burden of proof that there has been such an infringement. Depending on the nature of the obligation at issue such proof may involve substantial scientific evidence.[13] While the minimum standard of review with regard to complex assessments could, in principle, for the evaluation of such material, in practice this complexity is mostly an implicit consideration in the appreciation of the burden of proof. Ordinarily, it will be more difficult to demonstrate that Member State action broke EU law if the Member State had to act in an environment of scientific complexity.

Conversely, actions for annulment under art 263 TFEU as well as references on the validity of EU measures under art 267 TFEU address the legality of EU measures. In this context, the EU courts must directly deal with complex scientific or technical assessments and the balancing of competing interests that EU bodies need to conduct to arrive at these measures. Therefore, the Court developed a specific standard of review that is characterised by broad discretion that the competent EU institutions enjoy. The discretion relates in particular to the assessment of the facts in order to determine the nature and scope of the measures. Substantive review by the EU judicature only verifies whether the authorities have manifestly exceeded the limits of their discretion (manifest error test).[14]

This jurisprudence is not only an example of judicial self-restraint, but it is also a practical expression of institutional balance. It is based on the consideration that Union courts cannot substitute their assessment of scientific and technical facts for that of the institutions on which alone the legislature has placed that task.[15] These other institutions possess better technical and scientific expertise within the fields of their competence than courts of law. Therefore, they in a better position to conduct complex scientific assessments, such as the risk assessment of MMT. In addition, they usually enjoy a stronger democratic legitimacy than the courts because they are directly or indirectly responsible to an elected parliament.[16] This legitimacy justifies the balancing of competing interests. In the example of the MMT ban, the initiative for the ban actually came directly from the Parliament and it was taken up by the Council, that is by Member State governments responsible to their parliaments. In the absence of democratic supervision, as can be the case for specialised independent bodies such as the European Central Bank,[17] there is at the very least a democratic decision attributing a specific margin of appreciation to the body in question and this can be reversed by another democratic decision.

Conversely, the exercise of discretion comes with other obligations that are subject to stricter scrutiny. Specifically, the competent institution is under the duty to examine carefully and impartially all the relevant aspects of the individual case[18] and to comply with the procedural rules.[19] Essential components of the latter are specified by the right to good administration as laid down in art 41 of the Charter. While this provision only applies to EU institutions, Member State authorities applying EU law are subject to similar obligations resulting from a general principle of EU law.[20] These obligations include in particular the right of every person to be heard, before any individual measure that would affect him or her adversely is taken[21] and the obligation on the part of the administration to give reasons for its decisions. These reasons allow the person concerned and eventually the courts to appreciate the legality of the measure,[22] and in particular, whether the authorities have accurately examined the relevant facts. Therefore, a statement of these facts and of their appreciation should be part of the reasons given.

Compliance with these obligations is essential to the proper exercise of the discretion granted to the authorities. Irrespective of their technical competence and their democratic legitimacy, a decision of high quality requires the investigation of all relevant facts. Hearing the parties concerned helps to identify such facts because these parties often have specific knowledge of the situation on the ground and an interest to make it known. Therefore, EU environmental legislation[23] and international agreements[24] extend the right to be heard into rights to public participation with regard to decisions affecting the environment. In the case of the MMT ban the Court therefore considered it essential that Parliament and Council were able to point at studies that they relied on to arrive at their assessment of the risks and that in particular Parliament had conducted hearings with all stakeholders on this issue.[25]

Nevertheless, even with regard to these obligations judicial review will not always be exhausting. While courts can scrutinise strictly whether relevant parties had the opportunity to participate in the procedure or whether the competent institution gave sufficient reasons to explain a decision, in particular the question whether the institution examined all relevant aspects is more difficult to appreciate. For example, with regard to the MMT ban there was some dispute whether additional studies on the effects of MMT were necessary. The appreciation of this question obviously required another complex assessment. Therefore, the Court recognised that the discretion of the institution also relates, to a certain extent, to the finding of facts underlying their action.[26] The establishment of specific facts and of their relevance as well as the identification of scientific theories to be taken into account can be other areas of scientific uncertainty. Nevertheless, I would submit that that the EU courts have not yet fully explored how far this discretion extends. Most importantly, it may not be sufficient to apply the manifest error test in this regard. The courts should rather verify whether the institution undertook a reasonable, i.e. proportional, effort to identify the relevant facts and theories.

The jurisprudence on the application of the precautionary principle sustains this view and may be a step towards stricter review of administrative expertise. It requires, first, identification of the potentially negative consequences for health (or the environment) of the practice under examination, and, secondly, a comprehensive assessment of these risks based on the most reliable scientific data available and the most recent results of international research.[27]. In a similar vein, the Court has recently begun to underline that in applying EU environmental law Member State authorities must base their decisions on sound science and scientific data.[28] Otherwise, arbitrary outcomes would have to be feared.

These developments demonstrate a certain scope for the employment of independent experts by the European courts. However, up to now, there is extremely limited court practice of this type. Occasionally, the Court has invited the European Data Protection Supervisor as an expert on data protection issues[29] and, most recently, it has asked another EU expert body, the European Union Aviation Safety Agency, to explain certain issues of aviation security.[30] Apart from these isolated examples, however, it is still be up to the parties to relevant cases to submit convincing evidence, including expert testimony, to incite doubt of the administrative assessment. And it remains to be seen whether there can be cases where such doubt can move the European courts to call upon independent external experts.

Finally, one more dimension of judicial review needs to be mentioned because, in certain cases, the discretion on issues of substance is limited and therefore courts must examine such measures more intensively. Specifically, the Court has ruled that, where interferences with fundamental rights are at issue, the extent of the EU legislature’s discretion may prove to be limited, in the light of the principle of proportionality. This limitation depends on a number of factors, including, in particular, the area concerned, the nature of the right at issue guaranteed by the Charter, the nature and seriousness of the interference and the object pursued by the interference.[31] Thus, in view of the important role played by the protection of personal data in the light of the fundamental right to respect for private life and the extent and seriousness of the interference with that right caused by an unjustified comprehensive retention of communications meta-data, Directive 2006/24[32] was subject to strict review[33] and the Court ultimately declared it invalid. Apparently, this type of issue falls between the general category of issues where the EU legislator enjoys wide discretion and the limited category of issues that are beyond its powers, such as the death penalty that is prohibited under art 2 of the Charter. In this interim category, the EU legislator can, in principle, still act, but the Court will not limit review to the manifest error test. Conversely, most regulatory issues in the field of the environment only result in restrictions to weaker guarantees, such as the right to conduct an economic activity under art 16 of the Charter and the right to make use of property under art 17 and they have therefore not yet triggered strict review by the EU courts.[34] However, it is possible that the importance of the objective of an environmental measure, for example the protection of human health and human life, can justify stricter judicial scrutiny.[35]


To sum it up: In most cases the Court of Justice of the European Union limits substantial judicial review of EU measures based on complex scientific assessments and/or the balancing of competing interests to a manifest error test. Conversely, it reviews procedural requirements strictly, in particular with regard to the right to be heard and the completeness of the reasons given. When reviewing the application of EU law Member State courts must apply this level of scrutiny as a minimum standard, but under the principle of procedural autonomy Member State legal systems can provide for stricter substantial review.

*   Chambers of Advocate General Juliane Kokott, Court of Justice of the European Union, Luxembourg. The contribution only reflects the personal view of the author. He is grateful for the advice of Sascha Dalen Gilhuijs.


[1]  Paul FM Opdam, Mirjam EA Broekmeyer and Fred H Kistenkas ‘Identifying uncertainties in judging the significance of human impacts on Natura 2000 sites’ (2009) 12(7) Environmental Science & Policy 915 – 916; Christoph Sobotta ‘The European Union legal boundaries for semi-natural habitats management in Natura 2000 sites’ (2018) 43 Journal for Nature Conservation 263.

[2]  Art 1(8) of Directive 2009/30/EC of the European Parliament and of the Council of 23 April 2009 amending Directive 98/70/EC as regards the specification of petrol, diesel and gas-oil and introducing a mechanism to monitor and reduce greenhouse gas emissions and amending Council Directive 1999/32/EC as regards the specification of fuel used by inland waterway vessels and repealing Directive 93/12/EEC [2009] OJ L 140/88.

[3]  See Case C-343/09 Afton Chemical ECLI:EU:C:2010:419 paras 50 ff.

[4]  See to that effect Cases 33/76 Rewe-Zentralfinanz and Rewe-Zentral ECLI:EU:C:1976:188, para 5; C‑93/12 Agrokonsulting ECLI:EU:C:2013:432, paras 35 and 36); C‑572/16 INEOS Köln ECLI:EU:C:2018:100, para 42.

[5]  Rolf Svedberg ‘Natural Sciences in Environmental Law’ (2018) 27.4 European Energy and Environmental Law Review 140

[6]  Tiina Paloniitty and Kangasmaa Sinikka ‘Securing Scientific Understanding: Expert Judges in Finnish Environmental Administrative Judicial Review’ (2018) 27.4 European Energy and Environmental Law Review 125.

[7]  Franziska Grashof ’The ‘You Know Better’ Dilemma of Administrative Judges in Environmental Matters–A Note on the German Legal Context’ (2018) 27.4 European Energy and Environmental Law Review 151.

[8]  Chris Backes ‘Organizing Technical Knowledge in Environmental and Planning Law Disputes in the Netherlands–the Foundation of Independent Court Experts in Environmental and Planning Law’ (2018) 27.4 European Energy and Environmental Law Review 143.

[9]  See to that effect case C‑55/06 Arcor ECLI:EU:C:2008:244, paras 164 to 169.

[10] See with regard to the UK system Emma Lees ‘Allocation of Decision-Making Power under the Habitats Directive’ (2016) 28(2) Journal of Environmental Law 206 and 209 ff.; with regard to the Italian system Roberto Caranta ‘Still Searching for a Reliable Script: Access to Scientific Knowledge in Environmental Litigation in Italy’(2018) 27.4 European Energy and Environmental Law Review 158; and with regard to the Polish system Magdalena Bar ‘Scientific Knowledge in Environmental Litigation before Polish Administrative Courts: a Problem of Compliance with EU Law?’ (2018) 27.4 European Energy and Environmental Law Review 169.

[11] Cases C‑384/16 P European Union Copper Task Force v Commission ECLI:EU:C:2018:176, para 117; C-396/17 Leitner ECLI:EU:C:2019:375, paras 59 and 60.

[12] Cases C‑120/97 Upjohn ECLI:EU:C:1999:14, para 35; C‑211/03, C‑299/03 and C‑316/03 to C‑318/03 HLH Warenvertrieb and Orthica ECLI:EU:C:2005:370, para 76; and to that effect C‑379/08 and C‑380/08 ERG and Others ECLI:EU:C:2010:127, paras 60 and 61; C‑544/15 Fahimian ECLI:EU:C:2017:255, para 46.

However, it cannot be excluded that the Court of Justice expects a somewhat stricter review by Member State courts when they examine the implementation of EU law by Member State authorities than it would apply itself with regard to EU measures (Cf. Cases C‑723/17 Craeynest and Others ECLI:EU:C:2019:533, paras 34, 50 and 52; C‑197/18 Wasserleitungsverband Nördliches Burgenland ECLI:EU:C:2019:824, paras 70 ff.).

[13] Eg case C‑237/12 Commission v France EU:C:2014:2152 on Directive 91/676/EEC of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources (OJ 1991 L 375, p. 1).

[14] Cases C‑326/05 P Industrias Químicas del Vallés v Commission ECLI:EU:C:2007:443, para 75; C‑425/08 Enviro Tech (Europe) ECLI:EU:C:2009:635, paras 47 and 62; Afton (n 3), para 28; C‑77/09 Gowan Comércio Internacional e Serviços ECLI:EU:C:2010:803, para 55; C‑78/16 and C‑79/16 Pesce and Others ECLI:EU:C:2016:428, para 49; C‑44/16 P Dyson v Commission ECLI:EU:C:2017:357, para 53.

[15] Cases Enviro Tech (Europe) (n 14), para 47, Afton (n 3), para 28; C‑15/10 Etimine ECLI:EU:C:2011:504, para 60; C‑73/11 P Frucona Košice v Commission ECLI:EU:C:2013:32, para 75; C‑223/17 P Lubrizol France v Council ECLI:EU:C:2018:442, para 38.

[16] Juliane Kokott and Christoph Sobotta ‘The Evolution of the Principle of Proportionality in EU law – towards an anticipative understanding?’, in Vogenauer S and Weatherill S (eds.) General Principles of Law (Hart 2017) 169; Kokott J and Sobotta C ‘Judicial review and institutional balance with regard to European monetary policy’ in European Central Bank (ed) (2017) ECB Legal Conference, Shaping a New Legal Order for Europe–A Tale of Crisis and Opportunities 108.

[17] Cases C‑62/14 Gauweiler and Others ECLI:EU:C:2015:400, paras 68, 74, 81 and 91; C-493/17 Weiss and Others ECLI:EU:C:2018:1000, para 24.

[18] Cases C‑269/90 Technische Universität München ECLI:EU:C:1991:438, para 14; Industrias Químicas del Vallés (n 14), paras 76 and 77; Enviro Tech (Europe) (n 14), para 62).

[19] Case C‑350/12 P Council v In‘t Veld ECLI:EU:C:2014:2039, para 63.

[20] Cases C‑604/12 HN ECLI:EU:C:2014:302, para 49 and 50; C-141/12 YS ECLI:EU:C:2014:2081, para 67 and 68.

[21] Cases C‑277/11 M. ECLI:EU:C:2012:744, para 87 ; C-249/13 Boudjlida ECLI:EU:C:2014:2431, para 36.

[22] Cases Technische Universität München (n 18), para 14; C‑413/06 P Bertelsmann and Sony Corporation of America v Impala ECLI:EU:C:2008:392, para 69; C‑584/10 P, C‑593/10 P and C‑595/10 P Commission and Others v Kadi ECLI:EU:C:2013:518, para 100C‑300/11 ZZ ECLI:EU:C:2013:363, para 53.

[23] See in particular Directive 2011/92/EU of the European Parliament and of the Council of 13 December 2011 on the assessment of the effects of certain public and private projects on the environment [2012] OJ L 26/1 (the EIA Directive) and Directive 2001/42/EC of the European Parliament and of the Council of 27 June on the assessment of the effects of certain plans and programmes on the environment [2001] OJ L 197/30 (the SEA Directive).

[24] Eg the Aarhus Convention on access to information, public participation in decision-making and access to justice in environmental matters of 1998 [2005] OJ L 124/4 and the Espoo Convention on environmental impact assessment in a transboundary context of 1991 [2002] OJ C 104/7.

[25] Afton (n 3), paras 34, 36 and 37.

[26] Afton (n 3), para 33; C-5/16 Poland v Parliament and Council ECLI:EU:C:2018:483 para 151.

[27] Cases C‑333/08 Commission v France ECLI:EU:C:2010:44, para 92; Afton (n 3), para 60; C-487/17 Verlezza and Others ECLI:EU:C:2019:270, para 57.

[28] Cases C‑293/17 and C‑294/17 Coöperatie Mobilisation for the Environment and Others ECLI:EU:C:2018:882, paras 101, 104 and 110; C‑723/17 Craeynest and Others ECLI:EU:C:2019:533, para 51.

[29] Case C‑293/12 and C‑594/12 Digital Rights Ireland and Others EU:C:2013:845 – Opinion of Advocate General Cruz Villalón, para 22.

[30] Case C-74/19 Transportes Aéreos Portugueses, pending.

[31] Case C‑293/12 and C‑594/12 Digital Rights Ireland and Others ECLI:EU:C:2014:238, para 47.

[32] Directive 2006/24/EC of the European Parliament and of the Council of 15 March 2006 on the retention of data generated or processed in connection with the provision of publicly available electronic communications services or of public communications networks and amending Directive 2002/58/EC [2006] OJ L 105/54.

[33] Case Digital Rights Ireland and Others (n 31), para 48).

[34] Cf Case C‑416/10 Križan and Others EU:C:2013:8, para 113-115.

[35] Cases C‑488/15 Commission v Bulgaria (PM10) ECLI:EU:C:2017:267, para 106, and EU:C:2016:862, 105 – Opinion of Advocate General Kokott, para 96; C-723/17 Craeynest and Others v Brussels Hoofdstedelijk Gewest and Others ECLI:EU:C:2019:168 – Opinion of Advocate General Kokott, para 55.