The impacts of sea-level rise on European coasts in a 2°C world. Results and analysis of task 6.5 prepared as part of IMPACT2C: quantifying project impacts under 2°C warming

The European Union is at risk of the adverse effects of rising sea-levels, potentially leading to an increase in number of people affected by flood events and increased damage costs unless adaptation is undertaken. This research answers a question, ‘What are the impacts and costs of sea-level rise around Europe in a 2°C world?’ A 2°C world could occur rapidly under high emissions, or over much longer periods of time under climate mitigation. Climate mitigation is widely seen a way to reduce adverse risk, but in the coastal zone this is less effective and could only offer potential over very long time periods due to a time lag between atmospheric warming and oceanic response, known as the commitment to sea-level rise. As such, global mean sea-level in a 2°C world is projected to be between 0.11m (under high emissions) and 0.52m (under climate mitigation) higher than 1985-2005 levels under the HadGEM2-ES model. This makes quantifying impacts challenging.Using the Dynamic Interactive Vulnerability Assessment (DIVA) modelling framework, the number of people at risk from rising sea levels and flood costs have been analysed for scenarios of 2°C and extending up to a 5°C rise compared with pre-industrial levels in European Union coastal regions. Results indicate that following widespread European practices of continued protection, that between 5,300 and 7,000 people per year may be flooded in a 2°C world of climate mitigation – which could double if climate goes unmitigated. In a 5°C world, annual sea flood costs could be up to €1.2 billion per year, but reduce by one third under climate mitigation. The greatest costs occur around many countries surrounding the North Sea, where relatively, the EU’s smaller economies and small island states benefit most from climate mitigation.Adaptation remains particularly important, with sea dikes costing up to €3.9 billion per year in a 5°C world, decreasing by more than one sixth under climate mitigation. To achieve optimum benefits of adaptation and mitigation, it is essential that shoreline management and climate change adaptation are considered over the long time periods in which sea-level rise operates, taking into account multiple factors of coastal change. This includes a range of engineering techniques, including soft adaptation, accommodation and managed retreat, simultaneously considering wider societal needs and social acceptability of coastal change.<br/

Agent-based dynamics in disaggregated growth models

This paper presents an agent-based model of disaggregated economic systems with endogenous growth features named Lagon GeneriC. This model is thought to represent a proof of concept that dynamically complete and highly disaggregated agent-based models allow to model economies as complex dynamical systems. It is used here for "theory generation", investigating the extension to a framework with capital accumulation of Gintis results on the dynamics of general equilibrium.Agent-based models, economic growth.

Global-scale analysis of socioeconomic impacts of coastal flooding over the 21st century

Building on a global database of projected extreme coastal flooding over the coming century, an extensive analysis that accounts for both existing levels of coastal defences (structural measures) and two scenarios for future changes in defence levels is undertaken to determine future expected annual people affected (EAPA) and expected annual damage (EAD). A range of plausible future climate change scenarios is considered along with narratives for socioeconomic change. We find that with no further adaptation, global EAPA could increase from 34M people/year in 2015 to 246M people/year by 2100. Global EAD could increase from 0.3% of global GDP today to 2.9% by 2100. If, however, coastal defences are increased at a rate which matches the projected increase in extreme sea level, by 2100, the total EAPA is reduced to 119M people/year and the EAD will be reduced by a factor of almost three to 1.1% of GDP. The impacts of such flooding will disproportionately affect the developing world. By 2100, Asia, West Africa and Egypt will be the regions most impacted. If no adaptation actions are taken, many developing nations will experience EAD greater than 5% of GDP, whilst almost all developed nations will experience EAD less than 3% of GDP

Agent-based dynamics in disaggregated growth models

URL des Documents de travail : http://centredeconomiesorbonne.univ-paris1.fr/bandeau-haut/documents-de-travail/Documents de travail du Centre d'Economie de la Sorbonne 2010.77 - ISSN : 1955-611XThis paper presents an agent-based model of disaggregated economic systems with endogenous growth features named Lagon GeneriC. This model is thought to represent a proof of concept that dynamically complete and highly disaggregated agent-based models allow to model economies as complex dynamical systems. It is used here for "theory generation", investigating the extension to a framework with capital accumulation of Gintis results on the dynamics of general equilibrium.On présente le modèle Lagon generiC : modèle multi-agent pourvu de caractéristiques de croissance endogène. Il s'agit d'un prototype hautement désagrégé et dynamiquement complet qui permet la représentation d'économies comme des systèmes dynamiques complexes. Une application aux résultats de Gintis sur la dynamique des prix est également présentée

Understanding the drivers of coastal flood exposure and risk from 1860 to 2100

Global coastal flood exposure (population and assets) has been growing since the beginning of the industrial age and is likely to continue to grow through 21st century. Three main drivers are responsible: (1) climate-related mean sea-level change, (2) vertical land movement contributing to relative sea-level rise, and (3) socio-economic development. This paper attributes growing coastal exposure and flood risk from 1860 to 2100 to these three drivers. For historic flood exposure (1860 to 2005) we find that the roughly six-fold increase in population exposure and 53-fold increase in asset exposure are almost completely explained by socio-economic development (>97% for population and >99% for assets). For future exposure (2005 to 2100), assuming a middle-of-the-road regionalized socio-economic scenario (SSP2) without coastal migration and sea-level rise according to RCP2.6 and RCP6.0, climate-change induced sea-level rise will become the most important driver for the growth in population exposure, while growth in asset exposure will still be mainly determined by socio-economic development

Economy-wide effects of coastal flooding due to sea level rise: A multi-model simultaneous treatment of mitigation, adaptation, and residual impacts

This article presents a multi-model assessment of the macroeconomic impacts of coastal flooding due to sea level rise and the respective economy-wide implications of adaptation measures for two greenhouse gas (GHG) concentration targets, namely the Representative Concentration Pathways (RCP)2.6 and RCP4.5, and subsequent temperature increases. We combine our analysis, focusing on the global level, as well as on individual G20 countries, with the corresponding stylized RCP mitigation efforts in order to understand the implications of interactions across mitigation, adaptation and sea level rise on a macroeconomic level. Our global results indicate that until the middle of this century, differences in macroeconomic impacts between the two climatic scenarios are small, but increase substantially towards the end of the century. Moreover, direct economic impacts can be partially absorbed by substitution effects in production processes and via international trade effects until 2050. By 2100 however, we find that this dynamic no longer holds and economy-wide effects become even larger than direct impacts. The disturbances of mitigation efforts to the overall economy may in some regions and for some scenarios lead to a counterintuitive result, namely to GDP losses that are higher in RCP26 than in RCP45, despite higher direct coastal damages in the latter scenario. Within the G20, our results indicate that China, India and Canada will experience the highest macroeconomic impacts, in line with the respective direct climatic impacts, with the two first large economies undertaking the highest mitigation efforts in a cost-efficient global climate action. A sensitivity analysis of varying socioeconomic assumptions highlights the role of climate-resilient development as a crucial complement to mitigation and adaptation efforts

Adaptation to multi-meter sea-level rise should start now

Sea-level rise will fundamentally change coastal zones worldwide (Cooley et al 2022). A global two meters rise of sea level will be exceeded sooner or later within a time window ranging from one century to as long as two millennia, depending on future greenhouse gas emissions and polar ice-sheet melting (Fox-Kemper et al 2021). Here, we show that in addition to climate mitigation to slow this rise, adaptation to two meters of sea-level rise should start now. This involves changing our mindset to define a strategic vision for these threatened coastal areas and identify realistic pathways to achieve this vision. This can reduce damages, losses, and lock-ins in the future, identify problems before they become critical and exploit opportunities if they emerge. To meet this challenge, it is essential that coastal adaptation becomes core to coastal development, especially for long-lived critical infrastructure. Coastal adaptation will be an ongoing process for many decades and centuries, requiring the support of climate services, which make the links between science, policy and adaptation practice

Reply to “Global coastal wetland expansion under accelerated sea-level rise is unlikely”

We thank Törnqvist et al. for engaging with our modelling study on the future response of global coastal wetlands to sea-level rise (SLR) and their careful and critical discussion of the presented methods and results. However, we disagree with their suggestion that our modelling approach is inadequate, a claim which relies on two arguments: (1) they argue that our results are inconsistent with the “A/S (accommodation versus sediment supply) theory”; (2) they refer to coastal Louisiana as a case example where our modelling results would deviate from historic observations and future projections of coastal wetland change. However, below we will demonstrate that Törnqvist et al.’s application of the A/S theory is not valid to predict changes in coastal wetland area, and that our global predictions are in line with regional observations and projections for coastal Louisiana and the wider region of the Gulf of Mexico. Taking coastal Louisiana as an example, Törnqvist et al. highlight that ca. 6000 km2 of land are expected to be lost over the coming 50 years due to RSLR and the erosion/drowning of coastal wetlands. However, this figure cannot directly be compared to our results, because it does not account for upland areas being converted to wetlands as sea level rises; it only accounts for seaward losses due to erosion and/or drowning with associated shoreline retreat and land loss3. Equivalent scenario runs of our model (i.e. only considering wetland accretion, but no inland migration) result in a comparable projected wetland loss in Louisiana of ca. 6,900 km2 until 2100, under the medium SLR scenario (RCP4.5). This loss is triggered by insufficient sediment availability for the marshes to keep pace with SLR in situ. Hence, Törnqvist et al.’s claim that our model underestimates future wetland loss on the US Gulf coast is incorrect. Rather, we demonstrate that our global-scale model predictions of wetland losses are comparable to regional estimates

Global-scale analysis of socioeconomic impacts of coastal flooding over the 21st century

Building on a global database of projected extreme coastal flooding over the coming century, an extensive analysis that accounts for both existing levels of coastal defences (structural measures) and two scenarios for future changes in defence levels is undertaken to determine future expected annual people affected (EAPA) and expected annual damage (EAD). A range of plausible future climate change scenarios is considered along with narratives for socioeconomic change. We find that with no further adaptation, global EAPA could increase from 34M people/year in 2015 to 246M people/year by 2100. Global EAD could increase from 0.3% of global GDP today to 2.9% by 2100. If, however, coastal defences are increased at a rate which matches the projected increase in extreme sea level, by 2100, the total EAPA is reduced to 119M people/year and the EAD will be reduced by a factor of almost three to 1.1% of GDP. The impacts of such flooding will disproportionately affect the developing world. By 2100, Asia, West Africa and Egypt will be the regions most impacted. If no adaptation actions are taken, many developing nations will experience EAD greater than 5% of GDP, whilst almost all developed nations will experience EAD less than 3% of GDP

Preserving Access to Previous System States in the Lively Kernel

In programming systems such as the Lively Kernel, programmers construct applications from objects. Dedicated tools make it possible to manipulate the state and behavior of objects at runtime. Programmers are encouraged to make changes directly and receive immediate feedback on their actions. However, when programmers make mistakes in such programming systems, they need to undo the effects of their actions. Programmers either have to edit objects manually or reload parts of their applications. Moreover, changes can spread across many objects. As a result, recovering previous states is often error-prone and time-consuming. This report presents an approach to object versioning for systems like the Lively Kernel. Access to previous versions of objects is preserved using version-aware references. These references can be resolved to multiple versions of objects and, thereby, allow reestablishing preserved states of the system. We present a design based on proxies and an implementation in JavaScript