3
Regional Perspectives on Climate Tipping Points and Cascading Risk

The second day of the workshop focused on climate tipping points and cascading impacts and their interacting risks, highlighting different regional perspectives. The workshop participants first gathered in plenary to hear presentations about different geographical regions, including the coastal United States, American West, Arctic, and the Great Plains. The second part of the day included opportunities for broader participant interaction with a set of breakout sessions, followed by discussion on key takeaways.

COASTAL UNITED STATES: TIPPING POINTS IN FUTURE TROPICAL PACIFIC ISLAND SUSTAINABILITY

The day’s first speaker, Dr. Curt Storlazzi, U.S. Geological Survey (USGS) focused on the impacts of climate change on Pacific atolls, specifically sea level rise and wave-driven flooding. Atolls are low-lying, ring-shaped features built up on coral reefs, and Storlazzi explained that they have significant strategic, economic, and ecological importance because of their critical infrastructure, biodiversity, and locations within the nation’s Exclusive Economic Zones. Some examples include the northwestern Hawaiian Islands, the Marshall Islands, the Phoenix Islands, and the Gilbert Islands.

Storlazzi stated that unique characteristics of atolls leave them vulnerable. Atolls have very low topography with elevations of only 1 to 2 meters and steep offshore bathymetry. Each island has a limited freshwater lens, which, Storlazzi explained, provides the main source of freshwater and is critical for human habitability and the survival of many native endangered species. Infrastructure, critical habitats, and population centers of atolls lie at extremely low elevations. He explained that these characteristics make studying their risks and vulnerabilities translatable to other islands, such as American Samoa, Guam, Puerto Rico, and the U.S. Virgin Islands, because main population centers, infrastructure, and critical habitats are at low elevations along their shorelines.

Storlazzi next highlighted two current concerns related to atolls and low-elevation shorelines of higher islands. He noted that historically, wave-driven overwash events would occur every 20 to 30 years but are now happening multiple times per decade. This increase is attributed to rising sea levels, which have been increasing two to three times faster in the Western Pacific relative to the global average (Figure 3-1). Although a portion of this sea level rise is also driven by natural modes of variability, such as the Pacific decadal oscillation, Storlazzi noted with sea level rise of over one foot since 1990, implications for atolls that lie only 3 to 4 feet above sea level will become more severe.

The second concern Storlazzi emphasized is the interaction of sea level rise and waves. He pointed out that sea level rise through 2100 is expected to be 2 to 10 times higher than vertical reef growth rate (Montaggioni, 2005), which will lead to amplified wave-driven flooding and nonlinear flooding impacts, illustrated in Figure 3-2. This will cause greater inundation of infrastructure, freshwater supplies, agriculture, and habitats, Storlazzi emphasized.

Storlazzi presented his team’s work to assess the resulting impact of sea level rise and its nonlinear interactions with storm wave-induced flooding on island communities (Storlazzi et al., 2018). His team used a suite of models, including general circulation and regional climate models, a wave-driven flood model, and a freshwater availability model to project future wave-driven events under a range of sea level rise and climate change scenarios to determine tipping points, such as a loss of infrastructure viability and freshwater availability. They calibrated their models with field data, focusing on modeling typical storms with magnitudes that are expected to occur annually under future sea level rise scenarios. Storlazzi presented the key findings of Storlazzi et al. (2018), which identified that tipping points occur when wave-driven flooding events occur more frequently than freshwater lenses can recover, resulting in a loss of freshwater availability and, hence, loss of human habitability. Their results indicate such tipping points could occur as soon as 10 to 60 years from now. Storlazzi added that their simulations projected that in most cases, typhoons would become less frequent, resulting in less rainfall and smaller waves on annual scales. However, he pointed out that those typhoons are projected to be much more intense, which would suggest increased vulnerability for these islands.

Storlazzi emphasized that many atoll islands may become unsustainable for human habitation due to increased frequency and magnitude of wave-driven flooding from sea level rise. Many atoll islands may not be able to invest in expensive adaptation measures, such as seawalls, structure elevation, and desalination plants, he said. Without these adaptation measures, Storlazzi explained that the potential loss of habitability may force inhabitants to evacuate, which can potentially raise significant geopolitical questions around Exclusive Economic Zones and nationhood. Storlazzi ended by highlighting the urgent need for proactive adaptation strategies and international cooperation to address the vulnerabilities of atoll communities to climate change impacts.

AMERICAN WEST: SUMMER WATER IN THE WEST—CLIMATE TIPPING POINTS AND CASCADING IMPACTS

Next, Dr. Gordon Grant of the U.S. Department of Agriculture Forest Service and Oregon State University presented on challenges surrounding water management in the American West, with a focus on seasonal distribution of water, climate change impacts, and innovative solutions. Grant shared that his presentation was motivated by the paradox of water in the West, where precipitation primarily occurs during winter but agricultural, urban, and ecological water demand peaks during the summer (Figure 3-3). Grant indicated that the disconnect between the seasonality of water availability and demand requires effective storage solutions to bridge this gap. He outlined various storage mechanisms, both natural and engineered, that are critical for managing Western water resources, including snowpack, dams and reservoirs, and groundwater (Figure 3-4). He stressed that understanding the spatial and temporal dynamics of these storage systems is key to effectively manage water availability throughout the year, where their interplay may lead to tipping points and cascading impacts.

Grant emphasized that perhaps the most alarming trend and first potential tipping point in the future is diminishing snowpacks due to rising temperatures driven by climate change. He highlighted the rapid rate at which snowpacks are diminishing in both observations and models under median emission scenarios, with most models projecting the

complete removal of persistent snow from watersheds by 2050–2060. He then stressed the complexity of predicting the consequences for water availability due to the different rates of diminishing snowpack across diverse topography and noted that further research is needed to understand snowpack interactions with rivers, oceans, and vegetation on water availability and storage. He encouraged an integrated approach, combining satellite data, fundamental understanding, and modeling approaches.

Grant then focused on the next impact of diminishing snowpack—reservoir storage. As snowpack diminishes, Western states are experiencing significantly diminished low flows for reservoirs, he said. Grant discussed the need for adaptive approaches to address the challenges, such as potentially using forecasts to inform reservoir operations or reconsidering the legal and institutional frameworks that govern reservoir management.

Grant raised concerns around the depletion of groundwater resources, stressing that this could likely lead to emerging tipping points. He explained that intense utilization of valley aquifers for agricultural use has dramatically depleted groundwater resources. He shared that recent groundbreaking techniques in remote sensing coupled with volumetric measurements have provided improved insights into groundwater availability during droughts but that there is still a need to improve understanding of rates of change and time trajectories to inform groundwaters management. Grant highlighted the importance of addressing extraction rates and exploring the efficacy of recharge strategies to sustain groundwater levels, especially during droughts. He noted that research in these areas may inform open questions and challenges regarding groundwater availability and implications for agriculture, contamination, and potential adaptation strategies.

Grant introduced mountain groundwater, where large volumes of water are stored within the bedrock in volcanic landscapes, as an underappreciated component of the Western water landscape. Volcanic aquifers act as reservoirs for winter precipitation and then make up the majority of late summer river flow, Grant explained. According to Grant, integrating volcanic aquifers into the water storage strategies may potentially provide a beneficial tipping point to help sustain regions that are facing challenges using solely traditional surface water storage strategies.

He indicated that the potential opportunity provided by mountain groundwater also comes with unknown challenges, for example, uncertainty about where, when, and how much mountain groundwater is available and potential interactions with landscape disturbances, such as vegetation and fire. He highlighted the need for interdisciplinary research and integrated approaches to address various aspects of the complex landscape of Western water management. Grant emphasized the importance of understanding water dynamics, developing forecasting methods, and examining the interactions between water systems and ecosystems. Grant finished by suggesting the establishment of regional centers dedicated to studying integrated water problems, where collaborative research efforts could coalesce around natural and social dimensions, cascading impacts, and innovative water management solutions to address the challenges posed by climate change and growing water demands in the American West.

ARCTIC PERSPECTIVES

Societal Tipping Points to Shape Sustainable Change

Dr. Terry Chapin, University of Alaska, presented on the social dimension of Arctic tipping points. He focused his remarks on triggering positive social tipping points that can lead to sustainable outcomes for both nature and society and identified human drivers, global population growth, and resource use as key factors contributing to environmental changes. He explained that these changes include warming temperatures and the conversion of natural ecosystems to managed ones, leading to consequences such as species extinction and overexploitation of resources. Chapin pointed out that changes in the environment and ecosystems affect the benefits that society derives from nature. Using Alaska as an example, Chapin highlighted the challenge in balancing economic interests like oil extraction (a significant source of the state’s revenue), with growing climate change impacts on both nature and people in the region. He pondered how society might shift away from tipping points that further contribute to human drivers of environmental change toward tipping points that lead to a more sustainable trajectory.

Chapin introduced the concept of “stewardship” as a way for society to actively shape pathways of socio-ecological change, rather than respond to changes as they occur. He emphasized that stewardship involves intentional transformation that is oriented around goals for ecosystem health and human well-being. He asserted that these goals, while often posed as a choice between people and nature, are inextricably linked because humans are an integral part of nature and cannot, in the long term, benefit without interventions that support nature. Chapin posed two questions:

1. Can tipping points toward desirable changes be deliberately triggered?
2. If so, what are the desirable changes society would like to see?

He noted that deliberately triggering transformation may lead to both opportunities and risks and highlighted the importance of equity considerations.

Chapin outlined Olsson et al.’s three-phase framework for transformation: preparation, navigating change, and building resilience of the new system (Olsson et al., 2004). He explained the importance of defining the goals and strategic steps to determine the transformation and its trajectory during the first preparation phase, with scenario analysis being a helpful method. Chapin described the importance of identifying barriers, potential triggers for change, and potential allies for navigating change. To illustrate, Chapin provided the example of the war in Ukraine creating an opportunity for Europe to move away from dependence on Russian oil and toward development of renewable energy. Chapin added that being flexible in strategic approaches during the navigating change phase facilitates adaptation to the potential range of directions of change and maximizes the proportion of society that can be engaged in sustainability efforts, which increases the likelihood of the transformation success. Chapin added that building resilience into the new system in the third phase is also critical to prevent the new system from reverting to the old system.

Chapin drew from Donella Meadows’s work to describe different levers for triggering socio-political tipping points (Meadows, 2015). He noted the tradeoffs between the depth and scope of the transformation and the ease of its implementation (Figure 3-5). Chapin indicated that there are multiple possible pathways to create socio-political tipping points that could involve interactions between different levers. As such, multiple strategies tailored to specific contexts are warranted, Chapin emphasized. He described potential strategies that include shifting norms and behaviors, incentivizing sustainable production and consumption, and empowering society for change.

On shifting norms and behaviors, Chapin emphasized the importance of broadening society’s vision, one of the most difficult levers for triggering socio-political change. He described the societal focus on profit, material wealth, and comfort in the 19th and 20th centuries and stressed the need to shift societal values toward prioritization of human well-being and nature conservation. Chapin described how the stewardship framework may support this shift, because it focuses on developing complementary dimensions of human well-being, for example, natural capital and human capital. Chapin then discussed a set of survey results (Gaffney et al., 2021) from developed nations that suggest that most people believe human actions are driving toward a tipping point at the global scale and now favor a shift in focus from societal goals built around human well-being rather than profit. Despite this desire, the challenge of translating these values into actions remains, Chapin added. Chapin highlighted the important role of education and identity formation in shifting norms. He noted that indigenous groups in Alaska, though small in proportion, are widespread, and often have important values oriented around protecting nature. Showcasing their sustainable behaviors can increase awareness of key identities and values and encourage broader societal movement toward sustainability, he said.

Chapin described approaches to incentivizing sustainable production and consumption that could involve making structural adjustments, such as changing costs and benefits through incentives and disincentives, or taxes and subsidies, and improving rules around sustainable actions. In addition, he suggested that society can be empowered to create positive change toward sustainability by engaging nontraditional influential actors, fostering corporate citizenship, and exploring new democratic institutions. Chapin provided examples of this approach, including citizenship for nature as opposed to corporations, and citizen assemblies as opposed to conferences of parties for international negotiations. Finally, Chapin stressed the importance of initiating change at the local level, starting with individual behaviors, community engagement, and emphasizing co-benefits to garner larger public support and foster sustainable transformation.

Impacts of Arctic and Boreal Tipping Elements at Local and Global Scales

Dr. Michelle Mack, Northern Arizona University, focused her remarks on Arctic and boreal tipping points, with an emphasis on terrestrial elements and their impacts on climate through the carbon cycle. Mack highlighted that elements such as sea ice collapse and thawing permafrost are amplifying human-driven climate change and that the rate of warming is propelling elements toward tipping points with the potential for cascading risks through self-perpetuating positive feedbacks. She emphasized the complexity and interconnectedness of these elements within the Earth system and their potential to drive fundamental changes in global climate.

Mack detailed her focus on two elements of terrestrial ecology: permafrost (soils and sediments frozen for more than 2 years up to millennia) and boreal forests. She emphasized how both elements play critical roles in the carbon cycle because they hold globally significant reservoirs of organic carbon, on the order of petagrams (Pg; 10¹⁵ g) (Figure 3-6). Mack explained that permafrost and boreal forests exchange carbon with the atmosphere through photosynthesis and respiration, but these exchanges occur with substantial time lags. She noted that as the soil warms, carbon that was stored back in the Pleistocene (2.58 million to 11,700 years ago) may be released today. Mack stressed that the massive size of the carbon reservoirs represented by permafrost and boreal forests indicates that even small increases in the rate of exchange between these systems and the atmosphere can have globally important impacts on atmospheric carbon. Mack underscored the sensitivity of these carbon pools to climate warming, explaining that these exchanges are determined by “threshold behaviors.” In the case of ice and permafrost, Mack noted the threshold between frozen and thawed states, and for forests, the threshold between old and new growth. She explained that permafrost thaw has the potential to range from a regional to a global tipping point because of the vast amounts of organic carbon stored. She contrasted this with boreal forests, which she suggested are more likely to contribute to regional tipping points. Mack noted the potential for these regional tipping points to have cascading interactions with permafrost due to unique system-level behaviors, which can lead to subsequent global impacts.

Mack described in more detail the threshold dynamics of boreal forest carbon cycling and its cascading impacts on permafrost. She discussed the complexity of the role of wildfires in boreal forests, which historically have been part of the natural disturbance regime but are increasing in frequency and intensity in response to the warming climate. These changes contribute to increased amounts of energy released within and the impacts on the affected ecosystems. Mack noted that as the climate changes in the Arctic, the potential for feedbacks between the biosphere and the atmosphere also increases. She explained that warmer and drier climate leads to increased lightning activity, triggering more fires. These fires transfer carbon from the ecosystems to the atmosphere, triggering additional warming in a self-perpetuating positive feedback loop. She stressed that fire affects both carbon inputs and outputs, and hence can lead to shifts in ecosystem carbon balance over the fire cycle (100 to 1,000 years). Mack emphasized the highly complex nature of the fire cycle, explaining that fires could also lead to effects that potentially reinforce or counter positive feedbacks through processes that impact albedo, evapotranspiration, vegetative composition, and fire-vegetation interactions. These feedbacks could either increase or decrease the intensity of fire on the landscape.

Mack explained that boreal coniferous forests serve as long-term carbon sinks. She noted that recent increasingly severe wildfires exacerbated by climate change have been burning deeper into the soil layer, reaching deeper levels of “legacy” carbon from predisturbed ecosystems that have built up over millennia. If this legacy carbon is unlocked, boreal forest ecosystems may rapidly switch from carbon sinks to carbon sources for the

atmosphere, Mack explained. She described two other major impacts of this unlocking of legacy carbon on the long-term recovery of the carbon cycle: first, that historically dominant conifers are replaced by new species, and second, that permafrost can be exposed to higher air temperatures that accelerate its thaw. Mack compared two possible outcomes following severe fires that reach legacy carbon. She first described changes observed in Alaska, where fires reaching legacy carbon resulted in deciduous species replacing conifer, which can increase both carbon storage and resilience to fire. She contrasted the transitions observed in Alaska to those observed on the East Coast of the United States, where following a severe fire, the system failed to transition to deciduous species and coniferous species grew back. In these cases, the coniferous regrowth held less carbon but increased flammability. These two examples, Mack noted, highlight the range and complexity of the carbon and fire cycles in the boreal forest system.

Returning to permafrost, Mack explained that it is a legacy of previous climate and is not in equilibrium with the current climate because of the insulating effects from the organic layer of peat in the soil. She stated that in addition to gradual, top-down thawing, there is equal potential for rapid thaw. In these abrupt thawing scenarios, Mack explained that flowing water transports heat that creates concave areas in the ice, which traps warmer water against ice and leads to more ice melt—a positive feedback. Mack noted that within the next 100 years, wildfire is the most likely trigger for these abrupt thaws.

Mack presented different scenarios of future emissions of carbon dioxide and methane from permafrost carbon, illustrating how the amount and composition of these emissions highly depend on human-induced warming trajectories and their triggering and interactions with the complex feedback mechanisms of the boreal forest and permafrost elements. Mack then turned her remarks to what ecologists can do to impact these issues. From her perspective, she emphasized the need to reduce emissions and mitigate climate change to avoid the most severe impacts of permafrost thaw, the importance of broadening society’s vision to address the challenges presented by climate change in the Arctic, and the role of global networks of scientists, such as the Permafrost Carbon Network, in communicating and educating the broader public and policymakers on the importance of Arctic processes. She also stressed the need for scientific diplomacy among the United States and other nations, because 70 percent of the terrestrial Arctic lies within Russia.

Mack ended by emphasizing the need for interdisciplinary approaches to address the biophysical dimension of Arctic tipping points. She highlighted the importance of integrating social perspectives with ecological understanding to develop effective strategies for mitigating climate change impacts in the Arctic region. She encouraged creative harnessing of knowledge of natural and human systems to design new systems that can enhance the ability to deliberately trigger positive, rather than negative, outcomes.

GREAT PLAINS: TIPPING POINTS AND CASCADING IMPACTS IN NEBRASKA

Dr. Craig Allen, University of Nebraska—Lincoln, focused his remarks on tipping points and cascading impacts in the American Great Plains. He highlighted the Sandhills

and Platte River ecosystems in Nebraska. Allen noted that he would cover one example of a tipping point caused by a spatially contagious process⁶ and another caused by surpassing threshold behavior.

The American Great Plains are a grassland biome threatened by several sources, Allen explained, including land use change for human settlements and agriculture and the alteration of key processes such as fire for maintaining grasslands.

Allen first focused on tree invasion, a global phenomenon occurring in grassland across the globe, including Mongolia and Australia, as well as in the Great Plains. The Sandhills are around 20,000 square miles of grass-covered dunes that comprise much of the land area in Nebraska. He detailed historical conditions in the Sandhills as recounted by Parker, an explorer in the region in the 1850s, who described the region as being dominated by bare ground covered in sparse grass. By the 1860s, the landscape dramatically changed. Natural bison were replaced by cattle, and roads and railroads created ignitions that triggered severe wildfires that cleared grass from the dunes, Allen explained. Allen pointed out how early settlers recognized that mobile dunes were a potential alternative stable state for the region when grass was removed. To manage the land to avoid this potential tipping point toward a less-desired sand dune state, management efforts were made to inhibit fires and reduce herbivore pressure from grazing, he said (Figure 3-7). Allen explained that currently, the land is so highly managed to reduce the possibility of mobile dunes that some herbaceous plants are now endangered. This heavy management occurs despite the vast size of the area and extremely low population.

Allen explained that windbreaks (rows of vegetation or physical barriers used to provide shelter from wind) are extensively employed in the Sandhills because dry sandy soil can endanger the health and livelihoods of people and livestock, a primary industry in the region. These windbreaks are predominantly comprised of Eastern Red Cedar, which Allen noted is one of the only tree species suitable for the region but is also extremely susceptible to fire. Allen described how red cedar has spread very quickly across the Sandhills region because of wind and animal seed propagation. Although the windbreaks provide an essential ecosystem service, Allen explained, Nebraska is currently losing around 40,000 acres a year to emerging tree-dominated ecosystems. These ecosystems replace grasslands, reducing grassland and livestock productivity. Allen stressed that removing the cedar is not sufficient to restore the grasslands because of the associated loss of seedbanks and soil properties necessary for grasslands to thrive. He added that red cedar systems may also release carbon more easily than grasslands because their susceptibility to and intensity of wildfires is higher. Current efforts are underway to reintroduce fire to the region to help restore grassland properties in areas invaded by the red cedar, Allen noted.

Allen then spoke about flow regime changes in the Platte River, which is charged by snowmelt and has historically experienced heavy spring surge flooding, making it both wide and shallow. These flow regime changes maintained unvegetated landscapes critical

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⁶Spatial process that spreads contagiously, such as climate-sensitive disturbances like fire, land-use change, pests, and pathogens, and can drive changes in ecosystems, biogeochemical cycles, and land-atmosphere feedbacks (McCabe and Dietze, 2019).

for natural wildlife species but also historically disrupted local agriculture, he noted. Human interventions such as dams were put in place to manage variability in the water height and provide opportunities for energy production for electrification and irrigation for agriculture, Allen added. He explained that these interventions reduced flow variability and led to an alternative stable state. Allen explained that removal of the spring surge flooding, the

primary driving process of the river system, forced the system past a tipping point and toward steeper banks that eventually became vegetated, first with native species, but later with invasives and trees. The shift to wooded banks, Allen argued, tipped the Platte River into an alternative stable state that was largely beneficial to the human communities and agriculture. Ecologically, he pointed out, this new regime negatively impacted wildlife by removing natural environments of native bird species. Allen noted that in one actively managed 50-mile stretch of the river, efforts have been made to coerce the environment back to its pre-tipped state by cutting down vegetation and plowing sandbars. Although these actions help protect endangered species, Allen mentioned that these efforts are extremely costly ($200 million to date) and have been met with only partial success. Allen said that because of this program, the river exists in two states simultaneously, one a stable state created by previous interventions beneficial for humans and agriculture and another actively managed into a coerced state to benefit the native ecosystem. Allen stressed that many rare habitats are maintained entirely by this kind of coercive management, but these efforts remain costly and require continual maintenance to prevent the system from falling back into the surrounding stable state.

Allen then discussed how changes in grasslands are coupled with other global environmental regions and issues; for example, how reductions in productivity for grazing cattle in the Sandhills contribute to deforestation in the Amazon as beef production moves to those areas, or how changes to the Platte River increase agricultural productivity that contributes to hypoxic dead zones in the Gulf of Mexico. Allen emphasized that alterations in the grasslands, such as changes in groundwater extraction, nitrogen inputs, demographic characteristics of ranchers, and even market dynamics, all have the potential to be tipping points. Tipping these points, he added, may lead to cascading effects across the ecological, social, and economic systems that span local to global scales. Allen stressed that identifying tipping points is important, but anticipating the correct resulting stable state is challenging. He ended by reiterating that coercion can maintain a state when ecological systems are no longer sustaining those states on their own, but this strategy is expensive, temporary, and difficult to manage.

Q&A DISCUSSION WITH REGIONAL PERSPECTIVES: OVERARCHING THEMES

A moderated question-and-answer discussion followed each presentation in this session. The sections below summarize some of the key overarching themes from this discussion.

Integrated Approach

Across all of the discussions, speakers mentioned multifaceted and integrated approaches to address complex environmental challenges. They emphasized that scientific evidence, social dynamics, and ecological processes may be beneficial in decision-making and action. Storlazzi discussed advances in understanding the risks posed by melting glaciers and the need to connect these research efforts to adaptation efforts in the Pacific atoll

islands. Concerning challenges with water availability in the West, Grant underscored the importance of interdisciplinary research and innovative strategies to carefully address water-related challenges in a sustainable and long-term way. Chapin and Mack highlighted the need for evidence-based decision-making when addressing environmental issues in the Arctic. They all highlighted the importance of research approaches that integrate observations, experiments, and scientific evidence and connect the findings to environmental management efforts. Allen discussed the complexities of ecological management in the Great Plains, the benefits of an integrated approach to decision-making around management, and the need to consider ecological processes, social dynamics, and ecosystem resilience.

Adaptation, Mitigation, and Resilience

All the speakers cited adaptation, mitigation, and resilience urged caution about as critical concepts in addressing environmental issues. Ecosystem resilience and social resilience were emphasized, as well as the importance of the ability for communities to adapt to changing conditions. Storlazzi noted that both mitigation and adaptation strategies are crucial to address the impacts of sea level rise in the Pacific islands. He emphasized the need to reduce emissions while also recognizing the urgency needed to implement adaptation measures for vulnerable island nations. Storlazzi also discussed the adaptation strategies being implemented in atoll communities, such as small-scale measures to build more resilient infrastructure and seawalls and large-scale efforts like investments to raise islands’ elevation. Grant discussed the potential of mountain aquifers for adaptation strategies for resilience and highlighted the need to connect various adaptation strategies, such as forest and road management techniques, to capture snowmelt. Regarding building resilience in the Arctic, Chapin and Mack urged caution about the potential for unintended consequences of interference from adaptation and management efforts. Allen addressed the concept of ecosystem resilience, arguing that maintaining alternative stable states and thresholds can ensure resilience, and highlighted the complexities of balancing climate mitigation strategies with ecological considerations. He raised the potential for some strategies, such as afforestation, to have unintended long-term consequences, such as reducing resilience by negatively impacting local ecosystems and economies without having the desired long-term impacts on global carbon sources.

Communication and Engagement

Throughout the discussions, the speakers emphasized effective communication and engagement as essential components of efforts to address environmental challenges. Storlazzi noted that effective communication and collaboration will enhance sharing of research advances, as well as development and implementation of adaptation strategies relating to sea level rise and wave-driven flooding. He highlighted efforts to ensure that scientific research informs decision-making and action on the ground through engagement with local communities, government agencies, and international organizations. When asked by a participant about approaches to addressing misinformation, Chapin underscored

the significance of the scientific community engaging with the public to provide compelling information that directly relates to solutions and potential benefits of moving toward sustainability. Along the theme of communication, the session’s moderator, Dr. Dorothy Merritts, Franklin and Marshall College, highlighted the importance of effective science messaging and the use of clear and compelling storytelling to combat misinformation.

Uncertainty and Complexity

Each speaker acknowledged the uncertainties and complexities inherent in the environmental issues of their regions, particularly around future climate projections and the interconnectedness of ecological systems. Concerning the Pacific atolls, Storlazzi highlighted the uncertainty inherent in future scenarios regarding sea level rise and subsequent wave-driven flooding and their impacts. He pointed to the potential collapse of ice sheets as a major source of uncertainty when considering future scenarios and refining predictions to inform adaptation strategies in the Pacific atoll islands. Grant reiterated the complex and interconnected nature of the water system in the West. He acknowledged that the field is in the early stages of understanding of key processes such as groundwater recharge, spatiotemporal changes in mountain aquifer storage, and interactions between mountain aquifers and coastal water supplies, and stressed the need for advanced monitoring techniques to better address future challenges. Allen highlighted the interplay between social dynamics and ecological management strategies in the Great Plains, such as the complexity and uncertainty revolving around environmental management. He noted that drawing from their experience with the red cedar invasion, Nebraskans are hesitant to implement strategies such as afforestation. The speakers underscored the importance of ongoing research and monitoring to inform adaptive management strategies.

Balancing Human and Ecological Needs

A recurring theme throughout the speakers’ discussions revolved around the importance of balancing human needs with ecological conservation goals. Speakers with various regional perspectives touched upon this difficult but necessary balance and emphasized the importance of reconciling competing interests, considering trade-offs, and finding collaborative solutions that benefit both people and the environment. Storlazzi underscored the necessity to consider cost-benefit ratios for adaptation efforts in the Pacific atoll islands, which typically have smaller economies, as well as the importance of considering environmental justice issues. Grant noted that dam removal has both ecological- and energy-related considerations and discussed the need to reconsider the role of reservoirs in water management as environmental and energy challenges evolve. Allen described federally funded restoration and governance initiatives aimed at restoring the Platte River back to its natural pre-managed state, which also brings ecotourism to benefit local communities ecologically and economically. Allen suggested that such collaborative approaches to river management could consider both human and ecological needs.

The speakers’ discussions reflected a nuanced understanding of environmental challenges relating to tipping points and cascading impacts and recognition of the complexity and interconnectedness of social, ecological, and economic systems in addressing them effectively.

BREAKOUT GROUP DISCUSSIONS ON REGIONAL PERSPECTIVES ON CLIMATE TIPPING POINTS AND CASCADING IMPACTS

Workshop participants then had the opportunity to select one of four breakout discussions that focused on climate tipping points across each of the different regions presented earlier in the day. A rapporteur from each group was assigned to provide a brief summary of the key themes from their group’s discussion.

Arctic Breakout Discussion Themes

Dr. Tim Lenton, University of Exeter, summarized the discussion on tipping points in the Arctic. One theme he highlighted was the need to look across both natural and social systems in holistic ways to identify potential tipping points and associated cascades. Lenton noted that the group discussed the importance of “redrawing a map and a list of potential tipping points,” emphasizing that these tipping points would extend beyond physical systems into social ones, particularly for indigenous communities. Lenton also discussed coproduction of Western science and indigenous knowledge systems to better manage risks and seek positive social tipping points.

Coastal United States Breakout Discussion Themes

Dr. Kristen St. John, James Madison University, summarized the discussion on tipping points in the coastal United States. The first theme she focused on was on the importance of communicating science to ensure that the results are meaningful, and that stakeholders and community members are involved in the process from the beginning, which aligns with an identified need for regional coproduction of knowledge shared by Lenton. St. John also described the group discussion on uncertainty and unknowns and how to represent them in risk communication. She highlighted that something that is high risk but has many associated unknowns is not necessarily a low-likelihood event, which could introduce difficulties for decision makers. St. John noted that the breakout group also discussed the theme of transdisciplinary nature-based solutions for coastal areas that would have social and ecological co-benefits.

American West Breakout Discussion Themes

Dr. Michael Schoon, Arizona State University, summarized the breakout discussion on tipping points in the American West. Relating his comments to the previous discussion

of dramatic feedbacks in the Arctic, Schoon described a discussion around cascading impacts of drought through a cycle of water stress, fire, and additional emissions that feed back into more severe drought conditions. He mentioned a similar process for extreme heat and surface water temperatures. Schoon also highlighted the group’s discussion around transdisciplinary research opportunities, including the importance of a regional focus on infrastructure investments, geohealth, and the food-energy-water nexus.

Great Plains Breakout Discussion Themes

Dr. Simon Dietz, London School of Economics and Political Science, summarized the discussion on tipping points in the Great Plains. He highlighted several themes that were presented by the groups, including tipping points identified by Craig Allen in his presentation of the Sandhills and the Platte River, groundwater in the Ogallala aquifer, nitrogen thresholds for river systems, and precipitation thresholds for rain-dependent agriculture. Dietz noted that the group discussed research that has the capacity to examine teleconnections⁷ among environmental and socioeconomic factors between the Great Plains region and other U.S. regions and beyond.

Online Breakout Discussion Themes

Jonathon Tucker, staff member with the National Academies of Sciences, Engineering, and Medicine, summarized the discussion in the breakout group for online attendees. He highlighted challenges in balancing economies and land use in the Great Plains and coupling remote sensing capabilities with a variety of different model types (e.g., downscaled global climate models, regional precipitation models, groundwater models) to identify the potential for water storage in vadose zones, volcanic zones, and depleted aquifers.

Key Cross-Cutting Themes

Although each breakout session focused on a particular region, some key themes discussed in the plenary included:⁸

1. Holistic Approaches that consider both natural and social systems
2. Community Engagement and Coproduction from the outset
3. Uncertainty Management to improve risk communication for decision makers

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⁷A teleconnection broadly refers to a cause-and-effect relationship between remote regions caused by meteorological, societal, and/or ecological phenomenon. In physical Earth science, teleconnections refer to climate links between geographically separated regions (Nigam, 2003). Societal teleconnections are analogous to physical teleconnections, but rather refer to human-created linkages that connect activities, trends, and disruptions across different geographically separated social systems, communities, or regions (Moser and Hart, 2015).

⁸This summary of themes from the breakout session reflects the discussion of the group and should not be construed as reflecting consensus of the group.

4. Transdisciplinary Opportunities to explore social and ecological co-benefits
5. Identifying Regional Tipping Points to inform effective adaptation strategies
6. Research Priorities that leverage observation and modeling capabilities