## 6 Discussions and Research Opportunities  
Although the proposed roadmap in Figure 2 is partially based on six case studies in the UK and three case studies in the international context, we believe it is generally applicable to other seaports in the world with some adjustments to the timeline and the solution measures, since different countries may have different targeted years for net zero and different ports have different characteristics. Moreover, the IMO's 2050 net zero target can be used as a reference point. A few insights can be drawn from the roadmap:  
* The decarbonisation of seaports will take a time-phased approach as a progressive implementation process, especially for large seaports. * The categories of operational measures, technical measures, and fuel and energy measures have a direct impact on port emission reduction, whereas the categories of infrastructure measures, digitalisation measures, and policy and collaboration measures will support and facilitate the development and deployment of the solution measures in the first three categories; life cycle assessment and value chain analysis should be performed to ensure that emissions and costs are evaluated appropriately. * Operational measures are more readily available to apply in practice to reduce the fuel/energy consumption in port-associated activities. Advanced operational measures will be highly dependent on digitalisation measures and collaboration measures, because digitalisation and collaboration may revolutionise business processes, user behaviours, and relationships among port stakeholders; in addition, new business models and operational practices will emerge with the deployment of technical measures and fuel and energy measures. * Technical measures will be highly dependent on infrastructure measures and fuel and energy measures. Without the availability of supporting infrastructure and sufficient low-carbon fuel and energy, it will be difficult to decarbonise energy-intensive landslide equipment and vehicles and seaside vessels. * Fuel and energy measures require the development, implementation, and scaling up of relevant technologies such as hydrogen production, conversion, storage, and transportation; on the other hand, they also require the collaborative efforts and commitment from associated stakeholders, including governments, and the enforcement from legal regulations in the policy and collaboration category. Seaports have made good progress in reducing scope 1 and scope 2 emissions, as discussed in the case studies. However, it is often the scope 3 emissions that account for the largest share of emissions in the seaport geographical boundary. The roadmap covers all three scopes of emissions. There are a number of challenges and research opportunities in the process of implementing the roadmap. Firstly, operational measures have a certain limit in terms of decarbonisation if fossil fuels are used. Therefore, operational measures alone are not able to achieve net zero. Nevertheless, operational measures are preferable at early stages because of the uncertainty in technical measures, alternative fuels, and regulatory measures in the maritime sector. Moreover, operational measures will continue playing an important role to decarbonise seaports at later stages along with the adoption of other measures. In particular, there is a huge opportunity for developing effective operational measures enabled by digitalisation and collaboration measures. Secondly, there is a challenge of coordinating the implementation of technical measures, infrastructure measures, and energy measures. For example, the use of electric gantry cranes or shore power may cause overload of the port electricity network. At the Port of Southampton, cruise ships plugged in to the National Grid only 71 times over two years from 2021, whereas every year, there are over 500 cruise ship visits to the port.