Multiple climate change-driven tipping points for coastal systems.

As the climate evolves over the next century, the interaction of accelerating sea level rise (SLR) and storms, combined with confining development and infrastructure, will place greater stresses on physical, ecological, and human systems along the ocean-land margin. Many of these valued coastal systems could reach "tipping points," at which hazard exposure substantially increases and threatens the present-day form, function, and viability of communities, infrastructure, and ecosystems. Determining the timing and nature of these tipping points is essential for effective climate adaptation planning. Here we present a multidisciplinary case study from Santa Barbara, California (USA), to identify potential climate change-related tipping points for various coastal systems. This study integrates numerical and statistical models of the climate, ocean water levels, beach and cliff evolution, and two soft sediment ecosystems, sandy beaches and tidal wetlands. We find that tipping points for beaches and wetlands could be reached with just 0.25 m or less of SLR (~ 2050), with > 50% subsequent habitat loss that would degrade overall biodiversity and ecosystem function. In contrast, the largest projected changes in socioeconomic exposure to flooding for five communities in this region are not anticipated until SLR exceeds 0.75 m for daily flooding and 1.5 m for storm-driven flooding (~ 2100 or later). These changes are less acute relative to community totals and do not qualify as tipping points given the adaptive capacity of communities. Nonetheless, the natural and human built systems are interconnected such that the loss of natural system function could negatively impact the quality of life of residents and disrupt the local economy, resulting in indirect socioeconomic impacts long before built infrastructure is directly impacted by flooding.

Dynamic flood modeling essential to assess the coastal impacts of climate change.

Coastal inundation due to sea level rise (SLR) is projected to displace hundreds of millions of people worldwide over the next century, creating significant economic, humanitarian, and national-security challenges. However, the majority of previous efforts to characterize potential coastal impacts of climate change have focused primarily on long-term SLR with a static tide level, and have not comprehensively accounted for dynamic physical drivers such as tidal non-linearity, storms, short-term climate variability, erosion response and consequent flooding responses. Here we present a dynamic modeling approach that estimates climate-driven changes in flood-hazard exposure by integrating the effects of SLR, tides, waves, storms, and coastal change (i.e. beach erosion and cliff retreat). We show that for California, USA, the world's 5th largest economy, over $150 billion of property equating to more than 6% of the state's GDP and 600,000 people could be impacted by dynamic flooding by 2100; a three-fold increase in exposed population than if only SLR and a static coastline are considered. The potential for underestimating societal exposure to coastal flooding is greater for smaller SLR scenarios, up to a seven-fold increase in exposed population and economic interests when considering storm conditions in addition to SLR. These results highlight the importance of including climate-change driven dynamic coastal processes and impacts in both short-term hazard mitigation and long-term adaptation planning.

The long arm of climate change: societal teleconnections and the future of climate change impacts studies.

"Societal teleconnections" - analogous to physical teleconnections such as El Niño - are human-created linkages that link activities, trends, and disruptions across large distances, such that locations spatially separated from the locus of an event can experience a variety of impacts from it nevertheless. In the climate change context, such societal teleconnections add a layer of risk that is currently neither fully appreciated in most impacts or vulnerability assessments nor in on-the-ground adaptation planning. Conceptually, societal teleconnections arise from the interactions among actors, and the institutions that guide their actions, affecting the movement of various substances through different structures and processes. Empirically, they arise out of societal interactions, including globalization, to create, amplify, and sometimes attenuate climate change vulnerabilities and impacts in regions far from those where a climatic extreme or change occurs. This paper introduces a simple but systematic way to conceptualize societal teleconnections and then highlights and explores eight unique but interrelated types of societal teleconnections with selected examples: (1) trade and economic exchange, (2) insurance and reinsurance, (3) energy systems, (4) food systems; (5) human health, (6) population migration, (7) communication, and (8) strategic alliances and military interactions. The paper encourages further research to better understand the causal chains behind socially teleconnected impacts, and to identify ways to routinely integrate their consideration in impacts/vulnerability assessment and adaptation planning to limit the risk of costly impacts.