Accounting for climate change uncertainty through adaptation pathways

Climate change is having profound effects on marine systems such as coral reefs (Hughes et al., 2017) and those effects will become more pronounced in the coming decades, even with rapid emission reductions and climate mitigation measures (Frieler et al., 2013; Hoegh-Guldberg et al., 2014, 2017). Impacts may come from changes to:

• Disturbance regimes (e.g. extreme weather events)

• Ocean chemistry (e.g. acidification, dead zones)

• The way that people interact with the environment (e.g. fishing and harvesting).

The ecological consequences of these effects can include changes to the population dynamics, distribution and dispersal of species. This may culminate in losses of species locally and ecosystems becoming less biodiverse.

These pressures and impacts can reduce the ecosystem service benefits arising from MPAs and undermine the effectiveness of management actions. MPAs may need to develop new management approaches, and local communities may need to adapt as livelihood options and the liveability of coastal zones are altered.

It’s difficult to predict how ecosystems will change, particularly over longer periods. In the context of climate change, previous strategies for achieving management goals may no longer be effective (Ingeman et al., 2019), and it may not be possible to return to historical baselines (Hoegh-Guldberg et al., 2018). Cycles of ecosystem disturbance and recovery may be the new norm, and ecosystems that suffer severe impacts may transition to new, less biodiverse states that provide fewer ecosystem services (Grimm et al., 2013). There is also an increased risk of catastrophic loss (Hughes et al., 2017; Heinze et al., 2021).

As social, economic and biophysical systems change, management goals and priorities may also change over time. Today’s MPA management needs to account for uncertainty in decision-making – failing to do so is a high-risk strategy. This piece discusses an approach for making MPA planning and management more robust in the context of climate change.

Understanding uncertainty

There is uncertainty regarding how the climate will continue to change this century, and the subsequent impacts on marine ecosystems. The challenge for MPA planning and management is to maximize ecosystem integrity and ecosystem service provision over the coming decades despite these uncertainties and impacts.

In the context of decision support there are two key types of uncertainty:

Aleatory uncertainty refers to variation in a system, such as the natural variation in population numbers or weather conditions between years. Provided you can estimate this variance using methods such as surveys, historical monitoring data or modelling, you can account for it in decision-making to identify management strategies that are likely to be effective despite this variation. For example, understanding annual variation in fish stocks is important for identifying sustainable harvest rates.

Deep uncertainty refers to a fundamental lack of knowledge about a system that is an obstacle to predicting its future states. Because climate change is fundamentally altering physical, biological and social systems, accounting for deep uncertainty is imperative to identifying management strategies that will be effective across a range of possible future system states.

Climate change mitigation and adaptation

Addressing climate change impacts on MPAs involves identifying opportunities for mitigation and adaptation.

Mitigation actions directly target drivers of climate change in order to reduce impacts. These include reducing greenhouse gas emissions and increasing carbon sequestration and storageToo.

Although mitigation activities are essential for addressing the root causes of climate change in the long term, many climate change impacts on marine systems are unavoidable over the coming decades. So adaptation is also required to help people and ecosystems adjust to altered climate conditions (see Adapting MPAs to climate change).

But how do we decide what mitigation and adaptation measures to adopt in the context of MPA planning and management, when and where to adopt them, and what to do if they are unsuccessful?

Adaptation pathways to plan for future climate conditions

“Adaptation pathways” offer a planning framework that identifies sequences of actions that are likely to achieve desirable outcomes under a range of alternative future climate conditions (Fazey et al., 2016). A pathway refers to one potential sequence of actions over time, and several possible pathways are considered to address the uncertainty about how climate change will impact MPAs in the future. Because today’s management choices can restrict options in the future, it’s important to evaluate the long-term implications of each pathway (Wise et al., 2014; Fazey et al., 2016; Colloff et al., 2017; Costa et al., 2020).

Adaptation pathways can help you consider multiple possible futures and the value of these new or altered ecosystems to a broad spectrum of stakeholders.

Major advances in modelling alternative future climate scenarios reflect a wide range of possible climate mitigation activities and climate system models (Eyring et al., 2016; O’Neill et al., 2016). These models can be used as a basis for exploring how environmental conditions may change in marine ecosystems over the coming decades, and the implications of these changes for people and ecosystems (e.g. using risk assessment – see Carter et al., 1994; Jones, 2001; Warren et al., 2018 for examples of tools and methodologies that can be adopted in this context).

This type of scenario analysis helps to identify the spectrum of potential ecosystem states that may arise in the future, and how these may affect current or potential stakeholders and the ecosystem services they value (Evans et al., 2013; Maxwell et al., 2015; Costa et al., 2020). Importantly, long-term management may be able to improve the ecological and ecosystem service benefits that arise in each of the scenarios by avoiding or mitigating impacts and fostering adaptation.

Adaptation pathways require the assessment of critical thresholds beyond which the biophysical or socioeconomic systems may rapidly switch to alternative stable states (Costa et al., 2020). For example, ocean warming may lead to the transition from biodiverse coral reefs that provide nutritional, tourism and cultural benefits, to algae-dominated systems that provide few benefits (Hoegh-Guldberg et al., 2017). These “tipping points” are important in the planning process as they may require a substantial shift in management actions that can only be achieved with advance planning or further research and development.

Tipping points can be identified by observing how other MPAs have responded to climate change impacts, through the scientific literature or through expert assessment. By anticipating how and when these tipping points may occur, and their implications for nature and people, you will be better prepared to adopt additional adaptation strategies (Table 1; Walker et al., 2013).

The social and economic context of the pathways are also evaluated to determine when and what societal changes may be required to facilitate adaptation (Wise et al., 2014; Fazey et al., 2016). This is important because implementing some adaptation activities may require changes to legislation governing MPAs, additional funding or the approval of stakeholders. For example, species translocation and assisted gene flow activities may not currently be permitted under some protected area legislation. Effective planning for climate change adaptation must be coordinated across all levels of governance, and involve consultation with anyone who will be affected.

Importantly, adaptation pathways identify opportunities to interact with all domains of systems (physical, biological and social) in order to achieve long-term goals (Wise et al., 2014). The severity of climate change impacts can be strongly affected by interactions between these domains. For example, exposure to nutrients from agricultural run-off or wastewater discharge can make corals more sensitive to ocean warming. Several adaptation strategies (e.g., integrated land–sea management) aim to improve the resilience of marine ecosystems to climate change by reducing exposure to other pressures (see Table 1).

Key steps for adaptation pathways

Adaptation pathways provide a transparent framework where stakeholders can engage to inform the planning process, and that forms an ongoing cycle of management and learning in which new information is used to update planning over time. It has been applied in several real-world marine and natural resource management contexts (Haasnoot et al., 2013; Ranger et al., 2013; Bosomworth et al., 2017; Bloemen et al., 2018).

The key steps in developing this framework are to:

Mitigation measures and adaptation activities for MPA adoption 

Failure to account for uncertainties may leave you poorly prepared to deal with the most severe impacts of climate change. The adaptation pathways framework can help to facilitate robust long-term planning.

Several of the activities in Table 1 can serve both mitigation and adaptation functions. Many can be applied across a range of scales (national to community scales).

Table 1. Examples of mitigation and adaptation activities to make management of marine ecosystems more robust in the context of climate change.

Limitations and gaps

Global climate models are complex. They include a wide range of biophysical and socioeconomic pathways, and span a range of temporal and spatial scales. So it can be challenging to identify what the impacts of different climate scenarios will be on MPA systems (Freer et al., 2018).

Managing ecosystems in the context of climate change requires long-term planning, but short-term considerations are sometimes deemed more important than long-term outcomes. For example, political cycles occur over short timeframes (4-5 years), while addressing climate change requires coordinated multi-decade action.

There may be limited options for actions to conserve existing ecosystems. Protected area status and enforcement can be effective in limiting some human pressures (e.g. fishing, harvesting), but may be largely ineffective at reducing climate impacts. This underscores the need to evaluate a wide range of mitigation and adaptation actions, such as developing novel approaches to restoring ecosystems at scale.

Accounting for climate change in MPA management and planning is an iterative, long-term process. While we expect to resolve some uncertainties through research and monitoring, substantial uncertainty will always be present. Developing more robust approaches to accounting for uncertainty in decision-making is essential.