Editing IPCC:AR6/WGII/Chapter-14 (section)

== 14.6 Key Risks ==

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Ten key risks from climate change were identified for North American based on definitions and assessment approaches outlined in Chapter 16, which were extended to include the development of a risk database and analysis that included expert evaluation of interactions between climate hazards and sectors (Figure 14.11; SM14.3).

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[[File:b58112c2ec275709742f78c932dbd3d1 IPCC_AR6_WGII_Figure_14_011.png]]

'''Figure 14.11 |''' '''Rapid assessment of relative risk by sector (''' '''''y''''' '''-axis) and climate hazard (''' '''''x''''' '''-axis) for North America based on an assessment of asset-specific vulnerability and exposure across climate hazards (see SM14.''' '''3 for methodological details).''' For each unique combination, the hazard-by-sector risk was ranked as very high (very high risk and ''high confidence'' ), high (significant impacts and risk, ''high to medium confidence'' ), medium (impacts are detectable and attributable to climate change, ''medium confidence'' ), low or not detected (risk is low or not detectable). Blank cells are those where the assessment was not applicable or not conducted. Risks identified through the rapid assessment were further evaluated in the chapter assessments (see corresponding sector text for full assessment of risk and impacts).

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=== 14.6.1 Key Risks of Climate Change for North America ===

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In North America, divergent perceptions regarding the attribution and implications of climate change pose a key risk to adaptation mainstreaming (KR1). This lack of adequate adaptation in turn amplifies threats to human life and safety from intensifying extreme events, fires and storms (KR2). Climate change hazards pose risks to economic and social well-being (KR3), marine social–ecological systems (KR4), unique terrestrial ecosystems and their services (KR5), freshwater services (KR6), physical and mental health (KR7), food and nutritional security (KR8), and commerce and trade (KR9). Cumulatively, these risks interact to imperil the quality of life for North American communities, cities and towns (KR10).

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=== 14.6.2 Key Risks Across Sectors in North America ===

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===== KR1: In the public and policy domains, divergent perceptions of anthropogenic climate change which pose a risk of inaction on adaptation efforts to reduce exposure and socioeconomic vulnerability =====

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Complex factors, including individual beliefs, ideology, world view, partisan identity as well as societal context, influence how the public, as well as professional groups, communities and policymakers, perceive and understand climate change ( ''high confidence'' ) (Sections 14.3.3, 14.3.4). While there is expert scientific consensus on anthropogenic climate change, rhetoric, misinformation and politicisation of science have contributed to misperceptions ( ''high confidence'' ), polarisation on the severity of impacts and risks to society, indecision and delayed action ( ''high confidence'' ) ( [[#14.3.1|Section 14.3.1]] ). In North America, this impedes adaptation efforts ( [[#14.3.4|Section 14.3.4]] ) and inflates climate risks ( ''high confidence'' ).

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===== KR2: Risk to life, safety and property from intensifying extreme events =====

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Human life and safety across North America, and especially along the coasts of Mexico, the Hawaiian Islands, Gulf of Mexico, Atlantic Canada and southeast USA, will be placed at risk from SLR and severe storms and hurricanes, even at 1.5°C GWL ( ''very high confidence'' ) (Sections 14.5.2, 14.5.5; see Box 14.4). Warming, heatwaves and increases in wildfire activity in many regions of North America pose risks to air quality, health, lives and property (see Box 14.2). More extreme precipitation and flooding pose a risk to human morbidity, mortality and safety in fluvial flood zones and areas downstream of levees, dams and flood culverts. The increasing intensity of storm events poses a risk of landslides, erosion and flooding in shoreline and urban communities, especially high-bank areas along exposed coasts, in Arctic and temperate areas where winter sea ice has diminished and in low-lying coastal areas where SLR and storm surge often overwhelm existing natural coastal features and engineered structures ( [[#14.5.5|Section 14.5.5]] ; see Box 14.4).

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===== KR3: Cumulative damages from climate hazards which pose a substantial risk to economic well-being and shared prosperity =====

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Climate-change impacts are projected to cause large market and non-market damages ( ''high confidence'' ). By end of century under higher GWL scenarios (&gt;4°C), these damages are expected to reach several tens of billions of USD annually in Canada and hundreds of billions annually in the USA. Losses in labour productivity and wages, and damages to coastal properties, will be especially large; however, all sectors in the USA and most sectors in Canada are projected to see substantial relative damages on high-emission pathways by mid- to end of century compared with lower-emission pathways. Economic sectors with hard limits to adaptation (i.e., winter tourism) or that are highly affected by climate variability (i.e., agriculture and fisheries) will be at more risk at lower temperatures than other economic sectors (Sections 14.5.7, 14.5.8). Strategic implementation of adaptation strategies coupled with lower-emissions scenarios result in multi-billion-dollar reductions in economic damages ( [[#14.5.8|Section 14.5.8]] ; see Box 14.6).

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===== KR4: Risk of degradation of marine and coastal ecosystems, including loss of biodiversity, function and related services with cascading effects for communities and livelihoods =====

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Ocean warming will increase the frequency and intensity of MHWs (see Box 14.3), accelerate unprecedented rates of sea ice loss, and alter ocean circulation, chemistry and nutrient cycling in ways that profoundly impact marine productivity, biodiversity and food webs ( ''very high confidence'' ) ( [[#14.5.2|Section 14.5.2]] ). Collectively these impacts pose a risk to nearshore ecological and human systems ( ''high confidence'' ), increasing the probability of phenological mismatches, large-scale redistribution of species, and species population declines ( [[#14.5.4|Section 14.5.4]] ) with cascading impacts that strain cultural and economic systems reliant on marine productivity across North America ( ''high confidence'' ). Nearshore areas of Chesapeake Bay (USA) and Akimiski Island, mid-western James Bay and the coasts in the Pacific ranging from the Gulf of Alaska through Baja Peninsula, have a high proportion of species near their upper thermal limit, and are areas that are particularly susceptible to climate-change risk.

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===== KR5: Risk to major terrestrial ecosystems leading to disruptions of species, ecosystems and their services =====

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Major risks to terrestrial ecosystems across North America, such as semiarid landscapes, rangelands, boreal and temperate forests, and Arctic tundra, include significant ecosystem transformations and shifts in species abundances and ranges, and major vegetation types (e.g., transitions from forests to grasslands), with cascading implications for regional biodiversity ( ''very high confidence'' ). Warming increases the risk of permafrost thaw with propagating impacts on species and communities in the Canadian and US Arctic ( ''high confidence'' ) (CCP6). 6Forest disturbances, including wildfire, drought, insects and pathogens, are expected to increase with warming, acting synergistically to raise the prevalence of tree mortality and ecosystem transformation ( ''medium confidence'' ) ( [[#14.5.1|Section 14.5.1]] ). These changes will reduce services provided by terrestrial ecosystems, including timber yields and carbon sequestration ( ''medium confidence'' ).

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===== KR6: Risk to freshwater resources with consequences for ecosystems, reduced surface water availability for irrigated agriculture and other human uses =====

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Droughts and earlier snowmelt runoff will increase water scarcity during the summer peak water demand period especially in regions with extensive irrigated agriculture, leading to economic losses and increased pressures on groundwater as a substitute for diminished surface water supplies ( ''medium'' to ''high confidence'' ) ( [[#14.5.3|Section 14.5.3]] ). Streams in North America are expected to continue to warm, with important ramifications for aquatic ecosystems ( ''high confidence'' ), reducing habitat for salmon and trout species that are economically and culturally important ( [[#14.5.1|Section 14.5.1]] ). Warming and drying coupled with other stressors (e.g., pollutants, nutrients and invasive species) pose a risk to ecosystem structure and function in lakes, streams and reservoirs across many parts of North America ( ''high confidence'' ) (Sections 14.5.1, 14.5.3). Warming increases in heavy rainfall and nutrient loading pose risks for water quality and HABs ( ''medium'' to ''high confidence'' ) ( [[#14.5.3|Section 14.5.3]] ).

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===== KR7: Risk to human health and well-being, including mental health =====

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Heat-related human mortality is projected to increase in North America as a result of climate change and ageing populations, poverty, chronic diseases and inadequate public health systems ( ''very high confidence'' ) ( [[#14.5.6.1|Section 14.5.6.1]] ). Gradual changes to temperature and precipitation are impacting urban ecosystems and creating ecosystem regime changes resulting in the poleward expansion among insects that bring risks related to vector-borne diseases such as West Nile virus and Lyme disease ( ''high confidence'' ) ( [[#14.5.6|Section 14.5.6]] ). Climate change is expected to lead to wide-ranging mental health challenges related to an increase in the psychological burdens of climate change ( ''high confidence'' ), particularly for individuals with existing mental health conditions, who live in severely impacted areas or who are reliant on climate for livelihoods and cultural well-being (e.g., Indigenous Peoples and farmers) ( [[#14.5.6.8|Section 14.5.6.8]] ).

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===== KR8: Risk to food and nutritional security through changes in agriculture, livestock, hunting, fisheries and aquaculture productivity and access =====

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Cascading and interacting impacts of climate change threatens food systems as well as food and nutritional security for many North Americans, especially those already experiencing food and nutritional scarcity, women and children with high nutritional needs and Indigenous Peoples reliant on subsistence resources ( ''high confidence'' ) ( [[#14.5.6|Section 14.5.6]] ) ''.'' In agricultural regions experiencing aridification and where water scarcity precludes substantial expansion of irrigation, warming and extreme heat pose a risk to food and forage crop and livestock production ( ''high confidence'' ) ( [[#14.5.4|Section 14.5.4]] ). Ocean warming and MHWs will continue to disrupt commercial capture fisheries through species redistribution and changes to yield ( ''high confidence'' ), and warming waters and OA will increasingly impact aquaculture production ( ''high confidence'' ) ( [[#14.5.4|Section 14.5.4]] ). Interactions between competing aspects of human security (e.g., food, energy and water) will be exacerbated by climate change ( ''high confidence'' ) (Sections 14.5.3, 14.5.4, 14.5.8).

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===== KR9: Risks to major infrastructure supporting commerce and trade with implications for sustainable economic development, regional connections and livelihoods =====

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Climate change and extreme events are expected to increase risks to the North American economy via infrastructure damage and deterioration ( ''high confidence'' ), disruption to operations, unsafe conditions for workers ( ''medium confidence'' ) and interruptions to international and inter-regional supply chains ( ''medium confidence'' ) ( [[#14.5.8|Section 14.5.8]] ; see Box 14.5). These climatic impacts will have cascading implications for local livelihoods, sustainable economic development pathways and regional connectivity, and will reinforce pre-existing social inequities ( ''medium confidence'' ). Infrastructure damage will also disrupt economic activities, including manufacturing, tourism, fisheries, natural resource extraction and energy production ( ''high confidence'' ) ( [[#14.5.8|Section 14.5.8]] ).

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===== KR10: Risk to the quality of life in North American communities, cities and towns =====

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In major North American cities and settlements, vulnerability to climate change has increased and is projected to continue to rise ( ''medium confidence'' ) ( [[#14.5.5|Section 14.5.5]] ). Concentrated populations with unequal adaptive capacities, exposure of valuable assets, ageing infrastructure, and differing degrees of institutional capacity and effectiveness will underpin climate hazards ( [[#14.5.5|Section 14.5.5]] ). Coastal, riverine and urban flooding displacing communities and coastal ecosystems ( [[#14.5.5.2|Section 14.5.5.2]] ) will become a dominant risk to urban centres ( ''high confidence'' ) and will cause disruptions to transportation and trade infrastructure ( [[#14.5.8|Section 14.5.8]] ). Large wildfires endangering lives, livelihoods, property and key infrastructure, and economic activities will contribute to compromised air quality and municipal water contamination ( [[#14.5.6|Section 14.5.6]] ; see Box 14.2).

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=== 14.6.3 Cumulative Risk, Tipping Points, Thresholds and Limits ===

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Across North America, climate change poses a risk to social–ecological systems increasingly destabilised by compounding climate impacts and non-climate pressures ( ''high confidence'' ) (Sections 14.5.1–14.5.3) that erode the connectivity and redundancy underpinning system resilience (Sections 14.5.1–14.5.5; [[#Xiao--2017a|Xiao et al., 2017a]] ; [[#Koven--2020|Koven et al., 2020]] ; [[#Malhi--2020|Malhi et al., 2020]] ; [[#Turner--2020|Turner et al., 2020]] ). Accelerating climate change and increasingly severe hazards and shocks may induce abrupt changes or push systems, people and species to critical points–tipping points–where a small additional change causes a disproportionately large response, triggering feedbacks that lock systems into novel regimes ( [[#Scheffer--2001|Scheffer et al., 2001]] ; [[#Scheffer--2010|Scheffer, 2010]] ; [[#Anderies--2013|Anderies et al., 2013]] ; [[#Lenton--2013|Lenton, 2013]] ; [[#Iglesias--2020|Iglesias and Whitlock, 2020]] ; [[#Lenton--2020a|Lenton, 2020a]] ). Climate-change tipping points can compound and amplify climate impacts and risk, induce disparate climate burdens and benefits across human and ecological systems, and irreversibly restructure ecosystems and livelihoods (e.g., species extinctions, fisheries collapse, community-managed relocation) ( [[#Lynham--2017|Lynham et al., 2017]] ). Examples of systems with potential tipping points in North America include (a) permafrost and sea ice loss triggering transformation of ecological and human systems (including substantial shipping opportunities) in the Arctic that are permanent and irreversible except on geological timescales, and which are potentially underway ( ''high agreement, low evidence'' ) ( [[#14.6.2|Section 14.6.2]] ; see Box 14.3, CCP6), (b) mid-latitude forest ecosystems at low to middle elevations in western North America where wildfire and cumulative climate and non-climate pressures may restructure forests and succession in ways that promote transition to new vegetation types ( [[#14.5.1|Section 14.5.1]] ) and (c) agricultural communities in northern Mexico and the southwest USA where aridification and drought may interact with water resource policies, economic opportunities and pressures, and farm practices to induce either adaptation (via changes in irrigation practices) or farm abandonment, land-use transformation and livelihood changes (due to heat stress, soil deterioration or reduced economic viability) (Sections 14.5.3, 14.5.4, CCP6, [[#Yumashev--2019|Yumashev et al., 2019]] ; [[#Turner--2020|Turner et al., 2020]] ; [[#Heinze--2021|Heinze et al., 2021]] ).

Identification of critical thresholds, elements and connections within a system may also help identify potential positive tipping points, that is, focal components or processes in a system where a relatively small investment or intervention can induce a large benefit and enable self-reinforcing transformative adaptation ( [[#14.7|Section 14.7]] ; Chapter 17; [[#Tàbara--2018|Tàbara et al., 2018]] ; [[#Lenton--2020b|Lenton, 2020b]] ; [[#Otto--2020|Otto et al., 2020]] ). Under low-mitigation scenarios, compounding risks and higher-carbon-emission scenarios increase the potential that amplifying feedback loops and fatal synergies across sectors could lead to existential threats to the social–ecological systems of North America ( ''medium confidence'' ). Societal collapse has been linked to shifts in climate regimes, especially when societies have lost resilience due to slowly mounting social–ecological challenges, while other studies reveal that social continuity and flexibility enable historical climate resilience and prosperity under changing environments (FAQ 14.2; [[#Lenton--2019|Lenton et al., 2019]] ; [[#Otto--2020|Otto et al., 2020]] ; [[#Degroot--2021|Degroot et al., 2021]] ; [[#Richards--2021|Richards et al., 2021]] ).

Accounting for tipping points, interactions and reinforcing dynamics among ecological, social and climate processes is necessary for comprehensive analyses of climate-change risk, cost and urgency, as well as effective adaptation design and implementation ( [[#14.7|Section 14.7]] ; [[#Cai--2015|Cai et al., 2015]] ; Steffen and et al., 2018; [[#Lenton--2019|Lenton et al., 2019]] ; [[#Narita--2020|Narita et al., 2020]] ; [[#Dietz--2021|Dietz et al., 2021]] ). Multiple lines of evidence across sectors assessed in this chapter suggest that after mid-century and without carbon mitigation, climate-driven changes to ecological and social boundary conditions may rapidly push many systems into disequilibrium ( ''medium confidence'' ), emphasising the importance of prioritising adaptation actions with co-benefits for mitigation ( [[#14.5.4|Section 14.5.4]] ; see Box 14.3). Reducing climate hazards through mitigation and removing catalysts of system instability through adaptation measures that increase system resilience (e.g., ecosystem restoration) will help reduce the risk that systems move across a tipping point from a desirable to an alternate or undesirable state (Sections 14.5.4, 14.7; see Box 14.3; [[#Narita--2020|Narita et al., 2020]] ; [[#Turner--2020|Turner et al., 2020]] ; [[#Heinze--2021|Heinze et al., 2021]] ).

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=== FAQ 14.2 | What can we learn from the North American past about adapting to climate change? ===

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''The archaeology and history of Indigenous Peoples and Euroamerican farmers show that climate variability can have severe impacts on livelihoods, food security and personal safety. Traditional societies developed numerous methods to cope with variability but have always expanded to the limits of what those adaptations permit. Current knowledge and technology can buffer societies from many negative effects of climate change already experienced but will be severely challenged by the novel conditions we are now creating.''

People came into North America more than 15,000 years ago and have experienced both massive and minor shifts in climate ever since. At the end of the last very cold phase of the most recent Ice Age, about 11,500 years ago, temperatures rose extremely rapidly—as much as 10°C (18°F) in a decade in some regions. This undoubtedly contributed to the extinction of large mammals like mammoths and mastodons that people hunted alongside many other resources (see Cross-Chapter Box PALEO in Chapter 1). There were so few people on the land, though, and other resources were so abundant, that the long-standing human means of coping with climate variability—switching foods and moving on—were sufficient.

Following the end of the Ice Age, populations across North America grew for the next few thousand years, at a rate that increased once people began to domesticate corn (maize), beans and squash (the ‘three sisters’) as well as other crops. However, more people meant less mobility, and farmers traditionally are also more invested in their fields and remaining in place than foragers are to hunting grounds. Other means of coping with vulnerability to food shortage caused by climate variability included some continued hunting and gathering of wild resources, planting fields in multiple locations and with different crops, storage in good years, and exchange with neighbours and neighbouring groups.

According to archaeological evidence, however, these adaptation strategies were not always sufficient during times of climate-induced stress. Human remains showing the effects of malnutrition are fairly common, and conflict caused in part by climate-induced shortfalls in farming has left traces that include fortified sites, sites placed in defensible locations and trauma to human bone. Larger and more hierarchical groups emerged, first in Mesoamerica and then in the southwest and southeast USA as well as the Midwest USA. These groups offered the possibility of buffering poor production in one area with surplus from another, but they also tended to increase inequality within their borders and often attempted to expand at the expense of their neighbours, introducing new sources of potential conflict. Dense hierarchical societies also arose in other areas such as the northwest coast where agriculture was not practised but resources, such as salmon and roots, were abundant and either relatively constant or storable.

These societies were not immune to climate hazards despite their greater population and more formal organisation. Archaeological evidence strongly suggests that drought, or growing conditions that were too hot or cold, contributed to the decline of groups ranging from Classic-period Maya states in Mesoamerica, to the somewhat less hierarchical societies of Chaco in the southwest USA and Cahokia in the Midwest USA (Figure FAQ14.2.1). The usual pattern seems to be that climatic variability compounded social and environmental problems that were already challenging these societies.

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'''Figure FAQ14.2.1 |''' '''Examples of areas where past climate variability has contributed to crises.''' Climatic variability is most likely to lead to crisis when it is accompanied by social, demographic and political conditions or environmental mismanagement that compound climatic impacts on societies.

Still, Indigenous knowledge and traditional knowledge among Euroamerican farming communities provide guidelines for how to cope with ''traditional'' problems. Contemporary governmental restrictions (such as legal water-rights allocations, international borders and tribal-lands boundaries) have limited the adaptive capacity that Indigenous societies have developed over the centuries. Now human-caused climate forcing, if not mitigated by reducing heat-trapping GHGs, is expected to produce climates in North America that have no local analogues in human history even as it destroys heritage sites that are sources of knowledge about palaeoclimates and the diverse ways of coping with them that past peoples have discovered. Just as past peoples often ''avoided'' local climate change by moving on, in a world where mobility options are severely limited, a lesson from archaeology and history is that we should use our hard-won knowledge of the causes of climate change to avoid creating futures with no past analogues to provide useful guidance.

If societies in North America prior to the Euroamerican colonisation were vulnerable to climate variability, surely were not the more recent and technologically advanced societies of North America at lower risk? The 20th century Dust Bowl created in the US and Canadian prairies suggests otherwise. Severe drought conditions throughout the 1930s—which, to make matters worse, peaked during the Great Depression—did not cause either the USA or Canada to collapse. But both countries suffered massive economic losses, regional loss of topsoil and regional human strife (including loss of crops, income and farms) leading to migration. Yet anthropogenic global climate change was of little or no consequence in the 1930s. While farming practices made climate stress worse, the climate variability itself was either completely, or mostly, within the envelope of historical climate variability that earlier human societies had experienced.

Indigenous Peoples and Euroamerican farmers and ranchers have a long history of mostly successful adaptation to changing weather patterns. The wisdom held by Indigenous Peoples deep knowledge of how plants, animals and atmospheric conditions provide early warning signals of approaching weather shifts, and stories about how past communities have tried to cope with climate-related resource shortfalls. Long-standing community-level management of resources also helps prevent shortfalls, and institutions such as kin groups, church groups, clubs and local governments (which exist in communities of both Euroamericans and Indigenous Peoples, in different forms) can be powerful aids in ameliorating shortfalls and resolving conflict.

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=== FAQ 14.3 | What impacts do changes in the North American Arctic have within and outside the region? ===

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''The North American Arctic is warming at nearly three times the global average, creating a cascading web of local, regional and global impacts within and beyond polar regions. Changes in the Arctic not only effect global ocean circulation and climate regulation, but also facilitate new Arctic transportation routes and support transboundary resources with geopolitical, environmental and cultural implications as conditions change.''

Rapid warming and extreme temperatures in the Arctic is leading to unprecedented seasonal sea ice loss, permafrost thaw and increasing ocean temperatures. Cascading from these biophysical changes are cultural, socioeconomic and political consequences that are widespread and largely unprecedented in human history. Changes in sea ice create safety hazards for Indigenous Peoples and northerners who rely on frozen seas and rivers for transportation between remote communities and to subsistence hunting areas. Thawing permafrost, especially that of ice-rich permafrost, creates challenges and costs for a region with low population density and a small tax base to support major infrastructure investments. Warmer ocean temperatures induce large-scale distributional shifts and reduced productivity and access to the largest North American fisheries. Ice-associated marine mammals, such as polar bears, seals and walruses, have declined precipitously with decreasing sea ice in the Bering Sea, and widespread ecosystem changes from fish through birds and marine mammal species have altered the system with uncertain outcomes for these productive ice-driven ecosystems. Newly ice-free shipping routes are increasing regional and geopolitical tensions and may facilitate novel threats like the spread of invasive species and safety hazards to local hunters and fishers. The local and regional impacts of climate change in the North American Arctic are profound and span social, cultural, health, economic and political imperatives.

Although the region is remote, changes in the Arctic impact the rest of the world. The Arctic serves as a regulator of global climate and other ecological processes through large-scale patterns related to air and ocean circulation. These vitally important processes are nearing points beyond which rapid and irreversible (on the scale of multiple human generations) changes are possible. The magnitude of cascading changes over the next two centuries includes regional warming and temperature extremes, permafrost declines and sea ice loss beyond that experienced in human existence. This includes macro-scale risks related to SLR from the melting of glaciers and thermal expansion of oceans. Changes in the Arctic are more pronounced than elsewhere and portend climate-change impacts in other areas of the globe.

Adaptation in the Arctic is underway and lessons learned on what works and what is effective and feasible to implement can provide global insights. Successful adaptation in the North American Arctic region has been attributed, in part, to the explicit and meaningful inclusion of IK and Indigenous self-determination, and diverse perspectives in decision-making processes, strong local leadership, co-management approaches, technological investment in integrated climate modelling and projections, and multilateral cooperation.

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