Influencing the International Transport Regime Complex: The EU’s Climate Action in ICAO and IMO

Regime complexes entail a variety of institutions with a degree of overlap in terms of thematic issues and participating actors. The EU is such an actor engaging with other governmental and non‐governmental entities in the formation and evolution of regime complexes. In this article, we examine the role of the EU in the international transport regime com‐ plex, and more specifically in two of its core international organizations, namely ICAO and IMO. Our actor‐based approach focuses on how the EU navigates between these two constitutive components of the global transport regime complex, advancing climate change mitigation measures. Our empirical material shows how the EU’s active engagement in ICAO con‐ tributed to the organization’s shift vis‐à‐vis the role of the aviation industry in greenhouse gas emissions. Besides the EU learning process that occurred and led to a more engaging and less conflictual EU approach in IMO, the ICAO achievement increased pressure and created a more conducive environment for the respective recognition of the maritime industry’s share in climate deterioration. In this respect, the EU benefited from the structure of the transport regime complex to pursue its own preferences.


Introduction
International regime complexes derive from the need to address complex and multidimensional challenges that cannot be mitigated by individual actors or institutions.They entail a multitude of overlapping institutional settings and arrangements, each one dealing with different aspects of a broader issue area, from climate change and environment to security and human rights (Alter, 2022;Alter & Raustiala, 2018;Delreux & Earsom, 2023;Keohane & Victor, 2011;Raustiala & Victor, 2004).The European Union is an influential actor in such regime complexes, interacting simultaneously with its peers in these overlapping settings, following resources, legal competence, and membership statuses.
One of the least explored regime complexes is the international transport regime complex, which is structured around two core institutional pillars, namely the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO), which are both United Nations specialized agencies.The demographics of these two organizations highlight the impact the EU holds on them, with the EU 27 member states constituting 14% and 15,5% of ICAO and IMO membership respectively.In addition to membership figures, the EU has got the regulative capacity to articulate a regional sub-regime at the European level as well as the economic capacity to back it up.As a result, the EU can cast its impact on these two international organizations (Dikaios, 2022;Earsom & Delreux, 2021a;Gehring & Robb, 2018;Martinez Romera, 2018).
In this article, we adopt an EU-focused, actor-based approach across the two core international organizations of the transport regime complex.We argue that the EU interaction with ICAO had an impact on the IMO functioning as well by creating a more conducive environment for the EU to pursue its own agenda and advancing its own preferences on greenhouse gas (GHG) emissions mitigation measures.How has the EU navigated between the ICAO and the IMO?Our empirical insights answer this research question inductively by highlighting the main features of the EU strategy in both organizations.For this article, "the EU" will stand for both EU member states and EU institutions.
Our article is based on 23 interviews with key stakeholders that have been conducted in the period between 2019 and 2021, examining in essence the micro-level of the negotiating processes.The majority of the interviewees are officials of EU member states, as well as officials of the European Commission and the European Parliament.All the interviewees have at least once traveled to Montreal (ICAO headquarters) to negotiate the Carbon Offsetting and Reduction Scheme for Aviation (CORSIA) and/or London (IMO headquarters) to negotiate the Initial Strategy on the Reduction of GHG Emissions from Ships (henceforth: Initial Strategy).The period under examination begins around the time when the EU started being vocal regarding climate change towards the two organizations (in the late 2000s) and stops when the respective agreements were concluded, i.e., in 2016 for the former and in 2018 for the latter.A special focus is given in the periods before the conclusion of the agreements, as the European Commission of 2014-2019 had a special mandate to pursue rigorous actions toward GHG mitigation in the two international organizations (Juncker, 2014).
In the next section, we elaborate on the transport regime complex providing more information on the EU role and its modus operandi.Following that, we account for the EU action on climate measures in the two international organizations.Then, we highlight the interlinkages between EU actions, discussing the steep EU learning process that occurred as a result of EU engagement in the transport regime complex.We conclude by addressing the temporal and thematic generalizability of our findings.

The EU in the International Transport Regime Complex
The EU has been for long in the vanguard of international actors that call for action to mitigate the problem of GHG emissions.The EU record of actions has suffered from the ebbs and flows of international sentiment towards the problem.Broadly speaking, from 2007 to 2010, the international sentiment was not in favor of stricter climate measures due to the global financial crisis, as proven in the derailed Copenhagen climate summit, in 2009 (Skovgaard, 2014).The situation was reversed in and after 2015 when the Paris Agreement was adopted (Falkner, 2016).Following and building on this significant development, which owed much to the EU assertiveness (Pomorska & Vanhoonacker, 2016), the EU has attempted to restore its previously battered leadership role in shaping international climate rules (Bäckstrand & Elgström, 2013;Oberthür & Dupont, 2021), advocating ambitious climate targets in a broad array of sub-regimes.This trend has been boosted by the adoption of the European Green Deal (Eckert, 2021).
The multi-faceted nature of the GHG emissions problem entails a multitude of international fora within which GHG emissions and climate change are discussed (Earsom & Delreux, 2021b).Such fora are partially overlapping and non-hierarchical in nature, which are key features of a regime complex (Raustiala & Victor, 2004).Their broad thematic spread and differentiation, from natural emissions related to agriculture and farming activities to transport-related emissions linked with combustion and transport, generate a set of sub-regimes (Earsom & Delreux, 2021b;Keohane & Victor, 2011;Martinez Romera, 2018;Rajamani, 2020).Thus, combating climate change is developed based on sectoral approaches (Rayner et al., 2021;Sawa, 2010), which adds significantly to the fragmentation of the system and accentuates the difficulties in combatting climate change (Biermann et al., 2010;Doussis, 2020).The fragmented nature of the regime necessitates closer and more robust inter-organizational ties to enhance the governance effectiveness of the regime (Abbott, 2014).Hence, inter-organizational relations (within a sub-regime) and inter-(sub)regime links become critical factors in the smooth modus operandi of the overarching regime complex.
Since the late 1990s and early 2000s, the EU has focused on the contribution of transport to climate deterioration highlighting the role of the aviation and maritime industries.In this vein, it has developed intra-EU regulatory measures with a direct effect on third parties-states and economic entities like big companies.In addition, the EU has attempted to influence both the ICAO and the IMO on acknowledging and curbing the aviation and maritime industries share, exercising pressure on these two organizations for a broader regulatory regime along the EU's wishes.This two-edged strategy owed much to the realization that the two most relevant international organizations in the field are relatively rigid and diachronically slow in adapting to new conditions.Any decisions to tackle climate change would take much time and would most probably be too little, too late (interviews 6, 14; see also Oberthür, 2006).Without fully discrediting or considering irrelevant these international organizations, the EU rushed to the adoption of stricter climate policies and targets as a means to put pressure on them.Seen from a distance, unilateralism prevailed over the EU mantra of "effective multilateralism" and the emphasis it laid upon regulated international collaboration.
The EU has only observer status in both ICAO and IMO, which means that EU member states formally speak and vote in the working sessions of the two organizations.The EU/Commission Representative can only "take the floor" after member states have already spoken or by invitation of an EU member state.Because of that, extensive coordination among EU member states takes place in Brussels and regularly on the premises of the two international organizations prior to meetings and negotiations.The objective is to foster and ensure the necessary coherence for the EU to appear as a single block with a single voice (interviews 1, 19).These intra-EU negotiations usually strive to reconcile diverging interests, as well as opposition expressed to the EU institutions' proposals.This can be tracked by the ambiguity that exists around the competence status regarding the GHG emissions in aviation and shipping at the European level (interviews 13, 21; see also Earsom & Delreux, 2021a).Nevertheless, the EU (as a whole) more often than not appears with a single negotiating position, making itself an impactful actor, especially recently during the negotiations concerning the reduction of GHG emissions by the two organizations (interviews 10, 23; see also Dikaios, 2022).
Regardless of internal EU arrangements, the Union has consistent aspirations and policy action towards influencing the IMO and the ICAO to adopt policies that will secure that the aviation and shipping industries are cutting down their emissions.The EU actively engages in the Committee of Aviation Environmental Protection (CAEP), an ICAO Council technical body with only a few participating members that is responsible for developing and proposing adequate measures to the organization's Assembly.The CAEP consists of roughly 25 ICAO member states (the number varies according to the Assembly's mandate) that have a crucial role in global aviation.The Union has an observer status in the committee's proceedings.The same applies to the IMO's Marine Environmental Protection Committee (MEPC), which consists of all IMO members and deals with the broad array of environmental degradation caused by ships.

The EU's Climate Action in ICAO and IMO
Combating climate change became a distinct issue of international politics back in 1992 when, under the UN aegis, the UN Framework Convention on Climate Change (UNFCCC) was adopted.In 1997, the consequent Kyoto Protocol was adopted, explicitly mentioning that the ICAO and the IMO should act toward mitigating GHG emissions from the activities taking place under their authority.This reference was an indirect reprimand to these two organizations that they were not taking bold steps towards mitigating the contributions of international aviation and maritime activities to climate change.This statement holds by and large until today.Conversely to these two international organizations, the EU has been developing an incremental and forward-looking climate policy since 1992 (Dupont et al., 2018).This has granted the Union a leading role in international negotiations, promoting its standards and rules on how to mitigate GHG emissions (Wurzel & Connelly, 2011).ICAO and IMO have been primary targets of the EU's active engagement in the field.

The EU in ICAO
Right after the adoption of the Kyoto Protocol in 1997, the EU began to develop the EU emissions trading system (ETS), a today-prevailing, market-based measure aiming to tackle the rise of GHG emissions among the EU member states.The direct mention of ICAO in the Kyoto Protocol opened a new chapter in EU-ICAO relations.The EU stepped up its pressure and leverage to convince ICAO that more action was needed vis-à-vis the negative environmental imprint of international aviation activity.At the same time, GHG emissions from international aviation were rising, as reported by several international organizations and agencies (Albritton et al., 1997).This led to an intra-EU decision to include all flights that arrive or depart from European airports in its ETS.Following a long period of discussions and preparations, in 2008, the EU adopted the inclusion of aviation in the ETS through Directive 2008/101/EC, thus extending its own regulatory authority in a broader policy regime that was not under its exclusive jurisdiction.The Directive would be effective from 2012.The aim was that, by that time, the EU would have successfully advocated a similar global scheme at the ICAO, along the lines of the European one.However, this intention was never realized because of the fiery reaction of the non-EU ICAO member states (Lindenthal, 2014).Even before the entry into force of the Directive, in 2012, but mostly afterward, the international opposition against it was severe.Apart from a case filed against the Court of Justice of the European Union by the Air Transport Association of America and individual US and Canadian airlines, retaliation measures were also announced from some countries (Gehring & Robb, 2018).This openly hostile and very militant reaction was not expected by the EU officials and led to the EU retreat.Instead of the Directive, EU member states agreed on regulation by the seminal title "Stop the Clock," which reined back the implementation of the ETS in international flights (European Commission, 2012).This signaled a strategic defeat for the EU's flagship policy in tackling climate change; nevertheless, the EU has subsequently framed this episode as the first step towards the global system of CORSIA, for which systematic negotiations started in 2013 and which we will discuss below (interviews 14, 23).
Following this setback, the approach of the EU at the ICAO negotiations altered substantially.The abovedescribed unilateral and rather haphazard course of action gave place to a more systematic and comprehensive approach.The failed 2009 Copenhagen negotiations also played a significant role to this direction.In them, the EU appeared with an ambitious agenda, only to end up isolated and without any meaningful outcomes (Groen & Niemann, 2013).This undermined the EU's position as a global environmental leader and brought back home the message that a new approach was required to promote EU objectives in the field (Bäckstrand & Elgström, 2013).The deriving introspection generated, after 2010, a shift in the EU's global operation regarding climate change (Biedenkopf & Petri, 2019, 2021), which eventually culminated in the successful 2015 Paris Agreement.
At ICAO, this new strategic approach meant a more assertive but engaging EU environmental diplomacy.The EU officials realized that to maximize the EU's influence on ICAO, they should be ready to listen and make compromises, be open to other viewpoints and know whom to speak to (interviews 10, 17, 22).In the words of an EU official: "We had to spend about ten years to fix" the damage caused by the unilateral inclusion by the EU of international aviation to the EU ETS as well as by the offensive EU reaction to its first failed attempt to export the ETS system at ICAO (interview 23).
In the 2013 ICAO Assembly, a mandate was given to the CAEP to prepare a global market-based scheme that would be activated in 2020.The scheme was approved by the next ICAO Assembly, in 2016, with the EU being a key player in its development and eventual adoption.Without the EU's input and action, significantly less would have happened (interviews 10, 16, 17, 19, 21, 22, 23; see also Lin, 2017;Martinez Romera, 2018).The EU used its technical expertise as a spearhead and took advantage of its strong presence at CAEP to showcase that some of the options proposed are feasible.Out of the 22 members in 2013 and 24 in 2016, eight were EU member states, namely France, Germany, Italy, the Netherlands, Poland, Spain, Sweden, and the United Kingdom.The European Commission also participated as an observer, being able though to "take the floor" by sitting together with the member state leading the discussions (interviews 13, 15).Taking advantage of its numerical lead both within the CAEP and as a block of 28 countries, the EU created an extensive network where different EU member states were outreaching different third parties, and the EU delegation was outreaching everyone.All the EU delegates were advocating the same ambitious (in terms of comparison with the others) position, appearing as a solid block in favor of cutting GHG emissions caused by international flights.It is interesting to note that several voices complained about the EU having a single voice echoed repeatedly and fine-tuned by all EU member states and more than one vote.To overcome such criticism, EU member states decided that an "on-purpose communication divergence" would be beneficial to the common cause.A division of labor occurred in which each EU member state focused on different points of the EU argumentation for the importance of the policy when outreaching or taking the floor during the formal negotiations and informal deliberations (interviews 10, 13, 22).Characteristically, interviewee 13 said: "There are reactions from third countries that say if you are all supporting one thing, then you should get one vote, so we are instructed to differentiate sometimes." At the same time as this diplomatic frenzy at ICAO was taking place, the EU continued the implementation of its ETS in intra-EU flights, illustrating the feasibility of such a system.This provided the EU with an additional argument against the practicality of any such arrangement.Simultaneously, it boosted the expertise of the European Commission, which was always very well prepared to guide the EU member states, third countries, and the ICAO Secretariat through the technical needs that the pursuit of a sustainable aviation policy would require (interviews 10, 19).Additionally, the EU funneled EUR 6.5 million in a project called Capacity Building for CO 2 Mitigation from International Aviation in late 2013.This project's scope was to assist 14 countries in Africa and the Caribbean to adapt to the new climate reality of aviation in five years.However, it did not pay off as expected, as only seven states succeeded in their goal (Dikaios, 2022).
All the above, in combination with the favorable environment that the Paris Agreement had brought to international climate policy, the support of the Obama Administration (interviews 14, 15), and China's reversed position a few months before the final negotiation (Lewis, 2017) led to the adoption of CORSIA during the 2016 ICAO Assembly.It is evident, thus, that the final decision, which was also significantly watered down than initial (EU) expectations (Carpanelli, 2018), was a result of broader machinations with the EU playing an important role but not the sole one.

The EU in IMO
The IMO was much slower than ICAO in engaging with climate change after the Kyoto Protocol, even if the latter did not accomplish much.Although IMO recognized climate change as a problem in 1997 (Oberthür, 2006), it only adopted some first measures against it in 2011 (Shi & Gullet, 2018).During the same period, the European Commission took a more assertive stance on the GHG emissions from shipping activity.As a result, a number of EU documents and communications gradually underscored the need for the IMO to take substantial action (European Commission, 2011, 2013).This process resulted in an EU Regulation on monitoring, reporting, and verifying (MRV) GHG emissions from shipping in 2015.This Regulation, which is the first of its kind dealing with international shipping activity, focused on a process aiming to measure the emissions from ships.In contrast to the aggressive disposition that the EU chose to carry against the sector of aviation by including international aviation in the EU ETS, the Union adopted a milder legislation in the shipping sector, similar to what the IMO had already discussed in the previous period.
However, IMO's early actions on climate were rather sporadic without any mandatory measures being adopted (Oberthür, 2006).In addition, in 2015, the EU invested EUR 10 million in a project titled Capacity Building for Climate Mitigation in the Maritime Shipping Industry to run for four years (2016)(2017)(2018)(2019).The project was implemented by (and through) the IMO and created five centers of excellence around the globe, aiming to enhance technical cooperation, capacity building, and technology transfer regarding GHG emissions reductions from shipping activities, to alleviate disagreements that arose with the Initial Strategy (Dikaios, 2022), which introduced the reduction of GHG emissions from ships by 50% by 2050.
Furthermore, the EU engaged in organized diplomatic action to convince the rest of the 146 IMO member states of the need to contribute their fair share to the GHG mitigation efforts.It was again in 2015 when another opportunity emerged for the EU to take action: The Marshall Islands formed a coalition of the willing to promote climate action within the IMO, creating an ambitious position at the final negotiation of the Initial Strategy in 2018 (Corbett et al., 2020).In preparing the field for an ambitious strategy, a month before the respective IMO meeting, the EU adopted Directive 2018/410, pinpointing the Commission's responsibility to review the progress of the strategy.Directive implied that, if the IMO did not enact measures against GHG emissions, the EU would implement them on its own.This was an obvious warning to the IMO that the EU intended to adopt rigid unilateral regulation, which would affect maritime transport, by 2023, if IMO did not adopt an equally ambitious strategy.
In contrast to what happened in the ICAO case, the EU's approach to IMO was more structured from the beginning, without aggressive and unilateral actions.The institutional system that occurred after the 2015 Regulation was along the lines of the discussions held in IMO.Once it was established, it was easier for the EU to promote and advocate it in the IMO framework.Similar to ICAO, the EU's measures showed that "things are doable" (interview 20).To enhance this argument, the EU invested in capacity building, transferring know-how and the necessary technological experience to the rest of the world to follow a greener path in shipping activities.The EU aforementioned funded project curbed doubts, especially from developing countries, about the Initial Strategy (interviews 1, 6, 7).Moreover, during the preliminary negotiations (a couple of months before the final one), what played a significant role was the internal coordination of the EU, which kept the ambition high (interviews 2, 3, 4, 5).The EU did not want to compromise with an agreement setting low targets and having little if any impact.Hence, the EU entered the negotiations with an extremely high target of 70% to 100% emissions reduction by 2050.While the result was a 50% reduction by 2050, it was regarded as a success by the EU negotiators.The overshooting was intentional in order to secure a very ambitious goal agreement.At the closing stage of the negotiations, the 2018/410 EU Directive put additional pressure on the still hesitant states.However, this was used only as a last-minute maneuver to improve the EU alternative in case of a non-agreement and exercise negotiating pressure on the other side by worsening their own alternatives (Best Alternative to a Negotiated Agreement).This unilateral act was not perceived as a sign of arrogance and disrespect but rather as a true indication of the EU's dedication to a meaningful agreement.As a result, and following the paradigm of the Paris Agreement and CORSIA, IMO adopted an action framework of climate change mitigation, which owed much to the EU and constituted a decisive EU victory (interviews 7, 8, 9, 11, 12).Once again, of course, the goal stated in the agreement was lower than what the EU expected.If other groups or parts of the negotiation, such as the Small Island Developing States, wouldn't have been ready to agree on an initial mitigation target, or the industry hadn't given its consent (Corbett et al., 2020;Earsom & Delreux, 2021a), the result might have been different.
Bouncing back, the deal in London contained specific targets and was perceived by some EU officials as a public notice to ICAO to become more ambitious and set the barrier higher, warning-in a way-for further and fiery EU action towards that goal (Eickhout, 2018).

Navigating Within the International Transport Regime Complex
The following timeline (Figure 1) provides an overview of the EU engagement with the two international organizations of the transport regime complex, as well as some exogenous developments that had a catalytic role in the negotiations.
Although such international developments, like the Copenhagen and the Paris climate negotiations, were critical, the EU's gear shifting changed the pace and intensity of negotiations in the transport regime complex.It was only after the inclusion of international aviation in the EU ETS that the ICAO decided to develop a mechanism to contribute to the global efforts to reduce CO 2 emissions.This came up after the "Copenhagen failure," in a far from favorable environment towards bold climate change mitigation measures.The EU initiative eventually bore fruit and the mechanism was adopted in 2016, with much more favorable contours, one year after the adoption of the Paris Agreement.For the EU, the "ICAO saga" constituted a very useful learning experience.It had to retreat from its initial position, which was considered a great defeat by the EU officials (interviews 14, 19, 23) and had to regain the trust of its interlocutors within the ICAO.To achieve the latter, three courses of action were followed.First, it proceeded with the internal implementation of the ETS in aviation (flights within the EU) and based on this experience reverted to the ICAO with specific proposals on how such a system could work.Second, it devised and implemented a strategy of financing a part of the green transition in third countries, which led to a favorable view of the Union for these countries' governments.Third, EU member states realized that using their (multiple and individual) voices to advocate for the same goal would serve better the EU's interest.Applying they started approaching third ICAO members in a targeted way, utilizing different arguments adapted to the respective "audience" countries or groups of countries.
In the post-2015 favorable context, the EU adopted the MRV Regulation, sending a clear message to the IMO-albeit much milder than in the case of the ICAOthat it was time to take action regarding climate change.The lessons learned from the ICAO case vastly impacted the course of action of the EU towards the IMO.At the same time, the IMO had become aware of ICAO's course of action regarding GHG emissions and opposition was fading.Following ICAO's acknowledgment of the role of the aviation industry, the denial of the maritime industry's share by IMO was not sustainable in the long run (interviews 1, 6).Following EU pressure, and a revised EU strategic approach that incorporated lessons learned from ICAO, the IMO adopted the Initial Strategy in 2018.In contrast to ICAO, the EU first financed a project that promoted the green transition in shipping with beneficiaries from a multitude of countries to appease reactions and then started being more vocal about what needed to be done.and then adapt their policies in the other accordingly.This is clearly manifested in the EU case.
In the ICAO, the EU realized the hard way that unilateral action does not pay off and multilateral engagement is necessary in pursuit of the EU-desired outcome.This realization not only altered the way the EU approached ICAO but also led to the EU's shift vis-à-vis the IMO.As put by one official: "Active participation is a paramount dimension.Many crucial lessons on how to approach the IMO were learned from the experience of the delegations who went to the ICAO in 2013 and 2016" (interview 14).Exhibiting a steep learning curve, the EU realized that multilateralism was the only way forward for adopting climate measures in and by the international transport regime complex and followed a different course of action within the framework of climate change mitigation adopted by the IMO.The EU learning curve is important in accounting for the effective interaction with IMO but even more so is the effect of the successful ICAO precedent and its transcendence into the second forum of the transport regime complex.In a way, the EU induced a change that falls within the existing normative framework but alters the business-as-usual operation of the regime complex (Ruggie, 1982).
By pushing forward such a change in one component of a regime complex, the EU initiated a domino process, which would have had most probably an effect on IMO, even in the absence of any further EU action.This reinstates how one actor can intervene and have an impact on components of a regime complex even without having direct control or direct interaction with them (Margulis, 2021).
The interaction between the EU and the two organizations profited a lot from the overlapping negotiating representation of the EU in both organizations.Member states and the EU are usually represented in multinational negotiations by a multitude of bureaucratic agents and diplomats.The interlinking nature of GHG emissions from ships and aircraft suggests that there are potential benefits to be harvested by closely working administrative clusters that may have otherwise worked isolated and with little or no exchange of information and know-how.Contributing to EU negotiating coherence, the Commissioner of Transport and her directorate are responsible for both aviation and navigation.Violeta Bulc, then Commissioner, paid visits to both the ICAO and the IMO, held extensive talks with third parties, and highlighted the all-pervading will of the EU to move forward with its ambitious targets.In addition, some members of the European Parliament and key European-level officers were also involved in these missions.For example, interviewees 14 and 18 traveled to both international organizations prior to or during the negotiations of the CORSIA and the Initial Strategy respectively.In that respect, they built synergies between the two fora, advocating similar changes by use of a similar argumentation.This continuity plays well within a regime complex where different voices and interests arise.Having the same people negotiating, even in the backrooms, first, showcased the EUs firm stance and, second, contributed a lot to the steep learning curve that characterizes the EU intervention in the transport regime complex.
The EU learning process can be further seen in the similar use of financial resources in the two international organizations.Replicating the successful exercise of its "power of the purse" in other multilateral settings, the EU created a conducive environment to pursue an agenda mostly rejected or at best very lukewarmly accepted by most of the other participating states (interviews 1, 9).However, this emerged only after the failure of its unilateral action in the ICAO.The EU offered financial and technical assistance to specific recipients in an attempt to overcome their objections, targeting a number of states that perceived green regulation as an obstacle to their development (interviews 14, 18).This practice made its way to the EU strategy in IMO already at the beginning of the EU venture there, which is another demonstration of the EU learning process within the regime complex.
The "elephant in the room" of EU's interactions with the two international organizations of the transport regime complex is the heterogeneity of EU member states and their diverging interests.Although intra-EU politics do not fall within this article's scope, the EU member states did not have a common position until a couple of months before the respective negotiations in the IMO (Earsom & Delreux, 2021a).However, this divergence was overcome at the final stage of negotiations and the EU's eventual coherence contributed significantly to the successful outcome.An absence of the generated coherence would have compromised the learning effect of the negative experience in ICAO; moreover, the success of the IMO led to a rapprochement with the ICAO in pursuit of a more specific climate goal in the latter's climate policy.Hence, how the EU fares in a regime complex and whether the interlinkages between the complex's constituent components are taken advantage of depends a lot on the level of EU homogeneity in the specific regime area.Admittedly, more research is required on the effect of a regime complex on the coherence of multilateral actors, like the EU.

Conclusion
In this article, two arguments were made.First, we argue that the EU was significantly influenced by what was taking place within the ICAO and the IMO; second, that the EU substantially influenced the course of action of the two leading international organizations of the regime complex.Our analysis shows that the outcome of the negotiations with the two international organizations owes much to the EU stance which contributed to the successful conclusion of climate agreements in the international transport regime complex.Moving from one international organization to the other in this regime complex, the EU has gone through a steep learning curve, adjusting its engagement in IMO following its ICAO experience.This learning process can be seen not only in terms of the positions held and the EU's diplomatic modus operandi but also in the instruments used, especially the financial ones.The steepness of the learning curve owes much to the fact that the EU was represented in the two international organizations by largely the same EU officials, which ensured continuity but also a secure transmission belt of knowledge and know-how acquired in previous rounds of negotiations in the other international organization.The fact that the EU member states managed to bridge their differences was a sine qua non condition for effective EU interaction with the transport regime complex overall.
Studying the cases of the ICAO and the IMO through the spectrum of European climate diplomacy offers a clear and enlightening perspective of how the EU diplomatic apparatus has matured over time.Concurrently, it opens a few additional research paths that examine specific aspects of their relations with the EU, the broader picture of the wider regime complex function, as well as the way forward toward a new era, after the adoption of CORSIA and the Initial Strategy respectively.A number of interesting questions arise, including, for instance: What are some of the inter-organizational pressures coming from the international to the regional level, i.e., how do international organizations influence the action of the EU?In ICAO, the EU adjusted to these pressures by altering its own position vis-à-vis the inclusion of aviation emissions to the ETS.Given that the EU stated objective is to extend the EU ETS in shipping activities and pursue a new sustainable fueling policy for transport, it is interesting to monitor in the years to come to what extent the international interactions of the EU will affect the implementation of the European Green Deal.These questions, and many more, fall under the, far from simple, regime complex(es) of both transport and climate change and will surface in the coming years as the greening of the international transport sector moves forward, to become a reality.In this context, the EU's climate action will emerge as a catalyst not only between international organizations in the same complex but also among regime complexes.
The period under examination in this article was chosen for its significance for the future, since the way rules are established defines the way the regulated system will evolve (Zhang, 2016).Since the conclusion of the CORSIA and the Initial Strategy, a series of developments have taken place, leading potentially to a greener future in international transport.On the one hand, in the ICAO, albeit the disturbances caused by the Covid-19 pandemic, in late 2022, an agreement on a long-term aspirational goal towards mitigating GHG emissions from aviation has been reached.Right after, the EU, within the framework of the Fit-for-55 package, has moved forward with revising the application of the ETS in intra-EU flights by completely phasing out free allowances in emissions by 2026.Respectively, the CORSIA will be implemented in flights that arrive and depart from the EU and its effectiveness will be evaluated to introduce legislative changes, should it not deliver the expected outcomes (Council of the European Union, 2022).On the other hand, in the IMO, the majority of the Initial Strategy's precepts were left to be decided in the following sessions of the MEPCs.Further, due to the Covid-19 pandemic and the alienation from the belief that the IMO should contribute to the mitigation of GHG emissions, very slow progress has been observed in these MEPCs (IMO Arctic Summit, 2021).This fact made the EU, again under the Fit-for-55 declarations, start paving the way for unilateral acts in shipping, by planning to include the sector in the EU ETS scheme (Peter Liese, 2022).
The latter case might lead us to consider that, after all, the believes unilateral action to force other actors to follow down its path, although such action may backlash.Such a decision could also be the legacy of the unilateral experience in the ICAO.It remains to be seen how it will be received by the international community.
Timeline.Note: Exogenous developments that had a catalytic role in the negotiations in grey color.