Sea Level Rise Learning Scenarios for Adaptive Decision-Making Based on IPCC AR6

Adaptation decision-scientists increasingly use real-option analysis to consider the value of learning about future climate variable development in adaptation decisions. Toward this end learning scenarios are needed, which are scenarios that provide information on future variable values seen not only from today (as static scenarios), but also seen from future moments in time. Decision-scientists generally develop learning scenarios themselves, mostly through time-independent (stationary) or highly simplified methods. The climate learning scenarios thus attained generally only poorly represent the uncertainties of state-of-the-art climate science and thus may lead to biased decisions. This paper first motivates the need for learning scenarios by providing a simple example to illustrate characteristics and benefits of learning scenarios. Next, we analyze how well learning scenarios represent climate uncertainties in the context of sea level rise and present a novel method called direct fit to generate climate learning scenarios that outperforms existing methods. This is illustrated by quantifying the difference of the sea level rise learning scenarios created with both methods to the original underlying scenario. The direct fit method is based on pointwise probability distributions, for example, boxplots, and hence can be applied to static scenarios as well as ensemble trajectories. Furthermore, the direct fit method offers a much simpler process for generating learning scenarios from static or “ordinary” climate scenarios.

Völz, V., & Hinkel, J. (2023). Sea level rise learning scenarios for adaptive decision-making based on IPCC AR6Earth’s Future11, e2023EF003662.

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Co-creating a coastal climate service to prioritise investments in erosion prevention and sea-level rise adaptation in the Maldives

While the prioritisation of scarce resources for climate adaptation is becoming a priority for low and middle income countries, the climate service literature addressing adaptation prioritisation decisions is scarce. This paper contributes to filling this gap by presenting a co-creation process carried out in the Maldives among representatives of government, civil society and researchers. Together, we identified the need to improve a ranking method currently used by the Maldivian government to prioritise islands for investments in erosion prevention. As a solution we developed a layered index. The first layer of this index captures the objective dimension of the problem through an erosion hazard subindex, using the three variables wave energy, reef health and reef flat minimum width. The second layer captures the normative dimension through a multi-criteria analysis using the erosion hazard subindex as one criterion next to other stakeholder selected criteria such as critical infrastructure, economic activity, per capita income and the potential to house additional people that resettle from riskier places as sea-level rise progresses. Results of this new ranking method show that socioeconomic criteria were considered more important by the stakeholders than the biophysical criterion of erosion hazard. Among the top-ranked islands are many regional centres but also less populous islands that have a large potential to house additional people. Lessons learnt from the co-creation process highlight the importance of assembling interdisciplinarity teams, fostering mutual learning among project participants, and designing research projects that do not prescribe upfront the exact problems to be addressed and methods to be applied.

Hinkel, J., Garcin, M., Gussmann, G., Amores, A., Barbier, C., Bisaro, A., Cozannet, G. L., Duvat, V., Imad, M., Khaleel, Z., Marcos, M., Pedreros, R., Shareef, A., & Waheed, A. (2023). Co-creating a coastal climate service to prioritise investments in erosion prevention and sea-level rise adaptation in the Maldives. Climate Services, 31, 100401.
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Climate learning scenarios for adaptation decision analyses: Review and classification

Economic decision analysis is an important tool for developing cost-efficient adaptation pathways in sectors that involve costly adaptation options, such as flood risk management. Standard economic approaches, however, do not consider learning about future changes in climate variables even though a large literature on adaptive planning emphasises the key role of learning over time, because uncertainties about climate change are substantial. An emerging, diverse and fragmented set of economic adaptive decision making approaches, coming under labels such as real-option analysis or optimal control, have started to address this challenge by including the economic valuation of learning in the economic appraisal of adaptation options through making use of so-called climate learning scenarios. We synthesise this literature and classify the climate learning scenarios applied with respect to which climate variable is learned about, which learning sources are employed, how the learning is modelled, which climate data is used for calibrating learning scenarios, which goodness of fit information is provided and how deep uncertainty is handled. Our results show that publications consider learning through observations or do not explicitly state the source of learning. Most authors generate climate learning scenarios through stochastic processes or Bayesian approaches and use climate model output from the IPCC or the UK Met Office to calibrate the learning scenarios. The reviewed literature rarely provides information on the goodness of fit of learning scenarios to the underlying climate data. We conclude that most of the methods used to generate climate learning scenarios are not well-grounded in climate science and are inadequate to represent climate uncertainty. One avenue to improve climate learning scenarios would be to combine a Bayesian approach with emulators that mimic climate model runs based on observations from future moments in time.

Völz V., Hinkel J., Climate learning scenarios for adaptation decision analyses: Review and classification, 2023, Climate Risk Management,

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Decision-support for land reclamation location and design choices in the Maldives

Land reclamation in the Maldives is widespread. Current land reclamation practices, however, lack a systematic approach to anticipate sea-level rise and do not account for local flood risk differences to inform location and design choices. To address these limitations, this paper applies two decision-support tools: a hazard threshold analysis, and a cost-benefit analysis. Both tools produce site-specific estimates of land elevations or flood defence heights but do so for different goals. The hazard threshold analysis identifies hazard-based solutions that meet an acceptable flood probability for an intended lifespan without follow-up actions by reliability optimisation. The cost-benefit analysis identifies risk-based solutions using dynamic programming. We apply both tools to two land reclamation sites, a newly reclaimed airport island and a land extension of an inhabited island, in the Maldives. We find that total hazard-based heights for long-term planning horizons are highly uncertain, with local height differences of up to 1.9 m across sea-level rise scenarios by 2100. Risk-based Island elevations, in contrast, differ much less across scenarios, offering a practical advantage for decision-making. However, land reclamation choices on location, land elevation and investment in flood protection are not only driven by hazard-related aspects, such as reef characteristics, swell exposure, and sea-level rise, but also by estimates of exposed assets, reclamation, and flood protection costs. Taken together, the two decision-support tools are helpful for improving adaptation decisions and are also applicable in other small island regions.

Van der Pol T., Gussmann G., Hinkel J., Amores A., Marcos M., Rohmer J., Lambert E., Bisaro A., 2023, Decision-support for land reclamation location and design choices in the Maldives, Climate Risk Management,

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Making the UN Ocean Decade work? The potential for, and challenges of, transdisciplinary research and real-world laboratories for building towards ocean solutions

  1. Due to the strong interconnectedness between the ocean and our societies worldwide, improved ocean governance is essential for sustainable development in the context of the UN Ocean Decade. However, a multitude of different perspectives—ecological, societal, political, economic—and relations between these have to be understood and taken into consideration to foster transformative pathways towards marine sustainability.
  2. A core challenge that we are facing is that the ‘right’ response to complex societal issues cannot be known beforehand as abilities to predict complex systems are limited. Consequently, societal transformation is necessarily a journey towards the unknown and therefore requires experimental approaches that must enable the involvement of everyone with stakes in the future of our marine environment and its resources.
  3. A promising transdisciplinary research method that fulfils both criteria—being participatory and experimental—are real-world laboratories. Here, we discuss how real-world labs can serve as an operational framework in the context of the Ocean Decade by facilitating and guiding successful knowledge exchange at the interface of science and society. The core element of real-world labs is transdisciplinary experimentation to jointly develop potential strategies leading to targeted real-world interventions, essential for achieving the proposed ‘Decade Outcomes’.
  4. The authors specifically illustrate how deploying the concept of real-world labs can be advantageous when having to deal with multiple, overlapping challenges in the context of ocean governance and the blue economy.
  5. Altogether, we offer a first major contribution to synthesizing knowledge on the potentials of marine real-world labs, considering how they act as a way of exploring options for sustainable ocean futures. Indeed, in the marine context, real-world labs are still under-explored but are a tangible way for addressing the societal challenges of working towards sustainability transformations over the coming UN Ocean Decade and beyond.

Franke, A., Peters, K., Hinkel J., Hornidge, A., Schlüter, A., Zielinski, O., Wiltshire, K., Jacob, U., Krause, G., Hillebrand. H., 2022. Making the UN Ocean Decade work? The potential for, and challenges of, transdisciplinary research and real-world laboratories for building towards ocean solutions. People and Nature.

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The macroeconomic effects of adapting to high-end sea-level rise via protection and migration

Climate change-induced sea level rise (SLR) is projected to be substantial, triggering human adaptation responses, including increasing protection and out-migration from coastlines. Yet, in macroeconomic assessments of SLR the latter option has been given little attention. We fill this gap by providing a global analysis of the macroeconomic effects of adaptation to SLR, including coastal migration, focusing on the higher end of SLR projections until 2050. We find that when adapting simultaneously via protection and coastal migration, macroeconomic costs can be lower than with protection alone. For some developing regions coastal migration is even less costly (in GDP) than protection. Additionally, we find that future macroeconomic costs are dominated by accumulated macroeconomic effects over time, rather than by future direct damages, implying the need for immediate adaptation. Finally, we demonstrate the importance of including autonomous adaptation in the reference scenario of economic assessment studies to avoid overestimation of adaptation benefits.

Bachner, G., Lincke, D. & Hinkel, J., 2022. The macroeconomic effects of adapting to high-end sea-level rise via protection and migration. Nat Commun 13, 5705.

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Vested interests, rather than adaptation considerations, explain varying post-tsunami relocation outcomes in Laamu atoll, Maldives

Relocating communities out of increasingly risk-prone areas is effective for adapting to climate change. Relocations are particularly relevant for small island regions, where sea-level-rise-induced retreat from the coast will be inevitable for some communities. However, relocations are contested because communities are generally reluctant to move, and decision-makers face high political risks. As a consequence, relocations mostly occur after extreme events. In such situations, existing rules can be undermined by politics and power, driving relocation policy and resulting in varying relocation outcomes. However, these political and policy dimensions of post-disaster relocations have received little attention. Here, we study the politics and power dynamics of two post-tsunami relocations in the Maldives. Using process tracing, we find that vested interests, rather than adaptation considerations, explain varying relocation outcomes. Our findings highlight the complex power structures inherent in post-disaster relocations, which explain why similar events and drivers did not produce similar outcomes.

Gussmann, G. and Hinkel, J., 2021. Vested interests, rather than adaptation considerations, explain varying post-tsunami relocation outcomes in Laamu atoll, Maldives. One Earth.

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Uncertainty and Bias in Global to Regional Scale Assessments of Current and Future Coastal Flood Risk

This study provides a literature-based comparative assessment of uncertainties and biases in global to world-regional scale assessments of current and future coastal flood risks, considering mean and extreme sea-level hazards, the propagation of these into the floodplain, people and coastal assets exposed, and their vulnerability. Globally, by far the largest bias is introduced by not considering human adaptation, which can lead to an overestimation of coastal flood risk in 2100 by up to factor 1300. But even when considering adaptation, uncertainties in how coastal societies will adapt to sea-level rise dominate with a factor of up to 27 all other uncertainties. Other large uncertainties that have been quantified globally are associated with socio-economic development (factors 2.3–5.8), digital elevation data (factors 1.2–3.8), ice sheet models (factor 1.6–3.8) and greenhouse gas emissions (factors 1.6–2.1). Local uncertainties that stand out but have not been quantified globally, relate to depth-damage functions, defense failure mechanisms, surge and wave heights in areas affected by tropical cyclones (in particular for large return periods), as well as nearshore interactions between mean sea-levels, storm surges, tides and waves. Advancing the state-of-the-art requires analyzing and reporting more comprehensively on underlying uncertainties, including those in data, methods and adaptation scenarios. Epistemic uncertainties in digital elevation, coastal protection levels and depth-damage functions would be best reduced through open community-based efforts, in which many scholars work together in collecting and validating these data.

Hinkel, J., L. Feyen, M. Hemer, G. Le Cozannet, D. Lincke, M. Marcos, L. Mentaschi et al. Uncertainty and bias in global to regional scale assessments of current and future coastal flood risk. Earth’s Future: e2020EF001882. (2021)

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Risks on global financial stability induced by climate change: the case of flood risks

There is increasing concern among financial regulators that changes in the distribution and frequency of extreme weather events induced by climate change could pose a threat to global financial stability. We assess this risk, for the case of floods, by developing a simple model of the propagation of climate-induced shocks through financial networks. We show that the magnitude of global risks is determined by the interplay between the exposure of countries to climate-related natural hazards and their financial leverage. Climate change induces a shift in the distribution of impacts towards high-income countries and thus larger amplification of impacts as the financial sectors of high-income countries are more leveraged. Conversely, high-income countries are more exposed to financial shocks. In high-end climate scenarios, this could lead to the emergence of systemic risk as total impacts become commensurate with the capital of the banking sectors of countries that are hubs of the global financial network. Adaptation policy, or the lack thereof, appears to be one of the key risk drivers as it determines the future exposure of high-income countries. This implies in particular that the avoided costs in terms of financial stability should be weighted in as benefits of adaptation policy.

Mandel, A., Tiggeloven, T., Lincke, D. et al. Risks on global financial stability induced by climate change: the case of flood risks. Climatic Change 166, 4 (2021).

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Coastal protection can significantly reduce migration from sea-level rise

Protecting densely populated coastal areas, such as river deltas or megacities, from sea-level rise with dikes and seawalls will likely limit land loss and migration of people away from the coasts. But these protections are overlooked in most migration estimates. A new study predicts coastal protection could limit migration to 17 to 72 million people during the 21st century—less than half of some previous estimates.

The study, published in Earth’s Future, AGU’s journal for interdisciplinary research on the past, present and future of our planet and its inhabitants, is the first to look at the effects of coastal protection on migration rates on a global scale. The analysis takes into account a wide range of climate change and economic scenarios.

The authors find that, from a purely economic point of view, it makes sense to protect about 3% of the global coastline—mainly around densely populated cities and floodplains. However, for people living on less populated coastlines in poorer communities with fewer assets to protect, retreating would be a more affordable option for local governments than investing in protection.

“Nobody will give up New York City or the Netherlands, at least not in the 21st century, so we wanted to take this into account to get a more realistic picture of coastal migration due to sea-level rise,” said Daniel Lincke, a coastal researcher at the Global Climate Forum, an independent research institute focused on climate change research.

People have kept out the sea with dikes and other barriers for hundreds of years. The Netherlands, for example, began building dikes at least as far back as the 1200s. As sea levels continue to rise due to climate change, many countries will likely construct seawalls and other defenses to protect densely populated areas.

From a technical standpoint, Lincke expects that all coastal megacities potentially could be protected, at least up to the 2 meters (6.56 feet) of sea-level rise predicted by 2100 under the worst climate change scenarios. But building and maintaining coastal protection infrastructure comes at a high cost that could add up to several trillions (US$) globally through the 21st century.

Most studies have not considered coastal protection in their estimates of the impacts of sea-level rise, Lincke said, potentially leading scientists to overestimate the number of potential migrants from coastal areas.

“There have been global studies of cost-benefits of flood protection, and global studies on migration, but in this paper, they nicely combined them,” said Hans de Moel, a natural hazard risk researcher at Vrije Universiteit Amsterdam who was not involved in the study. “It’s important because you don’t want to look at adaptation measures in isolation.”

Lincke and his co-author Jochen Hinkel of the Global Climate Forum developed a model that splits the global coastline into about 12,000 pieces based on local elevation, population and socioeconomic data. For each piece of coastline, they used the model to estimate the local costs of constructing and maintaining protection, retreating from the land and losing its assets or repairing flood damage. They considered 250 potential future scenarios with differing amounts of sea-level rise and global wealth. Then they estimated the number of migrants, assuming that local governments would make protection decisions based purely on this cost-benefit analysis.

The researchers emphasize that their analysis focuses on economic factors, but that social and political factors also play powerful roles in how individuals and societies react to the threat of rising sea-levels.

For 3.4% of the world’s coastline, all of the scenarios agreed that coastal protection was a less costly option for the country than migration or repairing flood damage. These regions include coastal urban areas in China, Japan and Europe, and cities in the U.S., Australia, Indonesia and the Nile delta.

“You cannot protect everywhere—that will not be possible,” Lincke said. The analysis also takes into account the wealth level of each country and the local cost of constructing dikes. For regions with fewer people or less valuable property along the coasts, retreat and the likely migration of coastal residents is predicted to cost a country less than protection, which may guide decision-making. As a result, “it is very probable that the locations where people have to retreat are mainly in poor and developing countries,” Lincke said.

Densely populated countries in South Asia and Southeast Asia are predicted to have the highest numbers of migrants. Small island states, such as the Pitcairn Islands, the Marshall Islands and Kiribati, will also suffer high relative migration rates, with more than half the population of some islands likely being forced to move.

Depending on the scenario, sea-level rise is predicted to claim about 60,000 to 415,000 square kilometers (about 23,000 to 160,000 square miles) worldwide. The U.S., Russia and Canada are expected to lose the most land, as they have long and mainly sparsely populated coastlines.

de Moel suggests that the next step would be to look at models of how people decide when to migrate in the face of sea-level rise. These would include factors like a person’s risk perception, sense of place and the effects of previous extreme flooding events, like Hurricane Katrina in the U.S. and Cyclone Xynthia in France. He said that these events can trigger people to migrate well before their land becomes inundated. His group at Vrije Universiteit Amsterdam is working on such a model. “This is a very nice foundational piece on which we can move forward.”

Earth’s Future is an open access journal. The paper can be accessed under