Methods

We used an iterative process to develop the alternate futures for our Grand Challenge. For full details of the methods please see Nash et al. (in review). Here, we provide methods specific to our challenge. We identified 70 drivers, which were initially grouped into 12 umbrella drivers (Extended Data 1). To select drivers for incorporation into the alternate futures narratives, all authors were asked to evaluate each umbrella driver with respect to importance to the challenge and potential for society to influence the behaviour of the umbrella driver. A discussion of the results of this exercise highlighted that only those umbrella drivers that were directly linked to both human and ocean health had been selected as important with respect to the impact of the umbrella driver on the challenge. For example, ‘innovations in human health’ was considered to have a moderate to important impact on human health but was not perceived to have an important impact on ocean health. As a result, this umbrella driver only had a low to moderately important impact on the challenge overall. This result revealed a potential weakness of this step in the process, as it didn’t explicitly account for the indirect interactions arising from feedbacks between human and ocean health. As a consequence, we refined the umbrella drivers to an updated list of 5 umbrella drivers (in the main text, just termed ‘drivers’) for use in developing the alternate futures: (1) Worldview, decision-making context and approach to behaviour change; (2) Power and agency; (3) Human development and industry; (4) Food system; and (5) Lifestyle and connectedness to the oceans. We explored the potential trajectories of these drivers from Business-as-Usual to pathways that were more in line with the SDGs. Using published research relevant to each driver, we identified a series of descriptors of the drivers under the two 2030 scenarios (Table S1), based on likely and possible trajectories for the drivers. It should be noted that these drivers are not mutually exclusive, and overlap in many ways, as shown in the section on ‘Exploring the drivers that influence these alternate futures’.