Global assessments have typically developed scenarios to perform three related functions: focus scientific investigation and synthesis, integrate disparate models and data, and evaluate policies.
IPBES can use scenarios to coordinate and align scientific analysis by defining a diverse but limited set of future trajectories to use as inputs for scientific analyses. Scenarios can define inputs to models, policy analyses or comparisons, ensuring that different analyses are comparable and address a minimum shared set of issues. Such a knowledge base can be used to improve the robustness and relevance of future IPBES assessments. Narrative scenarios can also challenge the modelling community to develop new capabilities (Peterson et al. 2003).
Scenario development is an iterative process that can be used to integrate multiple disparate data sources, knowledge systems and models. Scenarios can integrate quantitative models of climate and ecological dynamics with qualitative analysis of processes that are not modelled or well understood, such as shifts in values, diets, or governance. Scenario development methods that use participatory modelling and mapping can also bring ILK into assessments, which is a priority for IPBES (Robinson et al. 2016).
Scenarios can be used to analyse the consequences of distinct and different choices or policies. Such analysis can assess the strengths and weaknesses of existing and future policies, as well as their robustness to future uncertainty. Furthermore, by connecting multiple domains of knowledge to a greater extent than integrated assessment models, scenarios can expand the diversity of novel policies and strategies that may provide opportunities for policy development or social innovation (Carpenter et al. 2006).
What types of scenarios should IPBES develop to best perform these three functions? Based upon previous experience we believe that there are three main options (see also Fig. 1).
Option 1: IPBES uses the most recent set of global scenarios for climate research and extends them for biodiversity and ecosystem services
The recently published global shared socioeconomic pathways (SSPs) (O’Neill et al. 2015) could provide a basis for the preparation of global IPBES scenarios. Developed for the analysis of climate change adaptation and mitigation, the five SSPs consist of stories that span a range of future trajectories of economic, social, institutional, and organisational variables. They have been constructed to enable their extension to non-climate issues, as well as to application at sub-national level (Absar and Preston 2015). However, using these global pathways to project changes in biodiversity and ecosystem services at multiple scales is a substantial undertaking that may oversimplify local social-ecological feedbacks and land-use dynamics that are critical for changes in biodiversity and ecosystem services (Oteros-Rozas et al. 2015; Reid et al. 2006).
Option 2: IPBES develops new global scenarios
IPBES could develop new scenarios focussed on how humanity benefits from and is reshaping biodiversity and ecosystem services. IPBES could build upon the methods developed by and lessons learned from the Millennium Ecosystem Assessment (MA), which was the first global assessment of ecosystem services (Millennium Ecosystem Assessment 2005a, b). The scenarios developed by the MA are less suitable as they are now a decade old and have not been widely used within either policy or scientific contexts. Developing new global scenarios would address the needs of IPBES, but would require substantial investments, including the development of new, multi-scale models and datasets to account for social-ecological tele-connections and cross-scale feedbacks that strongly shape land-use and ecosystem services.
Option 3: Bottom-up, diverse, multi-scale scenarios within a consistent global scenario context
IPBES could develop a diverse set of coordinated locally based scenarios that are linked to global scale scenarios. This proposal builds upon the existing work at the global level, but invests in developing new scenarios at the local scale, as well as in downscaling existing global scenarios. The rationale for this approach is that biodiversity and ecosystem services are strongly shaped by both local geography and local social-ecological dynamics (Reyers et al. 2013), which in turn are shaped by and reshape global drivers.
The impacts of global change vary across the world, and are shaped by local culture, preferences and wealth allocation. Local social and ecological diversity combine to produce responses that resonate out of their region. A top-down approach is likely to miss this heterogeneity and have difficulty engaging the diverse stakeholders, especially indigenous and local knowledge-holders.
A bottom-up approach can build on many local scenarios, stakeholder networks and local research capacities that are already in place, following examples such as the recent participatory biodiversity and conservation assessments by 60 communities in 20 different countries (Hall et al. 2015). IPBES could build upon these efforts and focus on the interactions among local trajectories and global dynamics. The regional assessments will highlight where it will be most useful to initiate locally based scenarios, given the current state of knowledge.
The advantage of this approach is that it would build upon existing analyses of large-scale global drivers, while acknowledging and using existing work to account for the social-ecological complexity of ecosystem services and biodiversity within landscapes. The challenge of such an approach would be coupling methods across scales, and managing the diversity of variables and knowledge systems needed to address different places. However, the experience of the MA suggests that it is easier to move from local to global than vice versa, because the knowledge and actions of local people, along with the characteristic behaviour of local ecosystems, have powerful effects on local dynamics and adaptation (Reid et al. 2006).