Globally, climate change is rapid and widespread and will continue through midcentury even if emissions are cut sharply, intensifying events such as extreme heatwaves, heavy rainfall, and drought.1 The acute and accelerating impacts outside of US borders on food systems, health, human well-being, built and natural systems, and economic sectors2 affect US national interests and compound the impacts of warming within the United States. The pace of emissions reduction and adaptation response would need to accelerate this decade both to limit warming to 1.5°C (2.7° F) or 2°C (3.6° F) above preindustrial levels and to build resilience to existing and future climate impacts (KMs 2.3, 32.1).2,3
Hellmuth, M.E., F.H. Akhtar, A.H. Cameron, C.A. Corner-Dolloff, G.D. Dabelko, T. Dinku, J.L. Koh, D. Mason, R.S. Pulwarty, L.I. Sperling, and M.F. Zermoglio, 2023: Ch. 17. Climate effects on US international interests. In: Fifth National Climate Assessment. Crimmins, A.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, B.C. Stewart, and T.K. Maycock, Eds. U.S. Global Change Research Program, Washington, DC, USA. https://doi.org/10.7930/NCA5.2023.CH17
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In a globally connected world, climate impacts can affect multiple sectors at once and have cascading effects that cut across sectors and geographies (KM 17.1). The direct impacts of climate change globally on people, ecosystems, and infrastructure, as well as the global transition to cleaner, lower-emissions technologies and economies, affect critical US interests including national security (KM 17.2); economics, trade, and investment (KM 17.3); and sustainable development (KM 17.4).
Despite documented evidence of increasing climate change risks, mitigation and adaptation responses by public and private sectors are not yet sufficient to avoid rising losses of life, biodiversity, infrastructure, and economic opportunity.1,2 Proactive early adaptation and mitigation action can reduce losses from climate change and extreme events, avoid locking in high emissions, and produce economic, social, and environmental benefits.4 In particular, inclusive approaches can help reduce risks, improve effectiveness of responses, and create opportunities for Indigenous Peoples, local communities, and other marginalized and underrepresented populations (such as women, youth, older adults, and ethnic minorities) who are especially vulnerable to climate impacts and energy transitions (KM 31.2). Adapting to a changing climate depends in part on the effective integration of climate information into decision-making at global, regional, national, and local levels (Box 17.1; KM 31.4).
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In a globally connected world, climate change impacts on US interests are multifaceted, interconnected, and frequently exacerbated by social unrest and environmental degradation (likely, high confidence). The scale and speed of climate-related impacts to US interests are expected to increase, due in part to underlying interdependencies and to the projected intensification of climate change (likely, high confidence). Emerging systems- and scenarios-based approaches to integrative planning are being applied to account for interdependencies and competing priorities (likely, high confidence).
Climate-related risks manifest across multiple systems, sectors, geographic domains, and timescales.19,20 Climate shocks in one or several parts of the built or natural system can lead to ripple effects around the world.21,22 Climate change impacts—alone or in combination with compounding stressors—can cascade across interdependent systems, magnifying risks not typically attributed to climate change. The effects of these impacts can spill across geographies and markets and, in turn, affect multiple US security, economic, and sustainable development interests (Figure 17.1; Focus on Compound Events). Moreover, traditional approaches to managing risk are inadequate given the compound and cascading nature of system risk, increasing the importance of accounting for system interdependency and uncertainty to reduce risk to US national interests.23,24
Climate change impacts affect the US’s security, economy, and sustainable development interests by reducing local and global stability, disrupting livelihoods and economic growth, increasing poverty and global inequality25,26 and compounding existing risks across US interests. For example, the Central American countries El Salvador, Guatemala, and Honduras are highly dependent on climate-sensitive agriculture, and climate change impacts disrupt rural livelihoods, health, and food security.27 Drought and extreme storms have impacted millions of Central Americans by exacerbating conflict and insecurity, requiring significant humanitarian resources and fueling unprecedented migration, including to the United States.28,29,30,31 Drought and extreme storms in Central America are expected to increase in frequency and severity due to climate change, threatening to further exacerbate these challenges.32
The combination of systemic global interdependencies and intensification of climate change is expected to increase both the scale and speed of climate change impacts.1,33 Climate change—including increasing temperatures, changing rainfall patterns, and increased frequency of some extreme events—combines with stressors such as conflict, land degradation, biodiversity loss, population growth, and worsening human health to exacerbate food insecurity and potential famine.34 For example, climate extremes have increased the incidence of multiple concurrent or consecutive breadbasket failures (e.g., poor harvests in major food-producing regions), threatening global food security and leading to cascading effects (e.g., social unrest and higher prices) across multiple geographies that affect US interests.21,35,36 Since 2018, multiple stressors, including droughts in North America and the Horn of Africa, poor harvests in China and France, the COVID-19 pandemic, and the war in Ukraine have combined to severely test global food security, increasing fertilizer costs and food prices and decreasing food availability.37
Given the right conditions, however, interconnectedness can help mitigate risk. For example, food imports can address localized food insecurity and may become more prevalent given climate change impacts.20,38 Transformative changes in human behavior that lead to “positive tipping points”—including the adoption of new technologies (e.g., energy transition to lower-emissions technologies) or approaches (e.g., regenerative agriculture approaches that increase climate resilience and sustainability of farm and food systems)—can help prevent the worst-case impacts of climate change.39
Traditional risk assessment and management approaches tend to focus on single sectors or locations rather than systems and the related complex interdependence of risks.16,40 However, approaches to decision-making that address adaptation and mitigation early in the process at a systems level, considering the fullest suite of risks, interactions, and optimal response options, are advancing (Ch. 18).41 Integrating responses vertically (across global, regional, and local levels) and/or horizontally (e.g., multistakeholder partnerships to codesign landscape-scale responses) offers promising insights for addressing these interdependencies across multiple scales and sectors.42,43,44,45 Scenario planning, “nexus” approaches that address multiple sectors, and other co-development and participatory approaches are being applied to plan in the face of uncertainty, address linkages, and consider the role of response options themselves as risk drivers (Chs. 18, 31).20,40 More experience is needed in applying and evaluating these emerging approaches to improve policy coherence and coordination across sectors and to better understand sensitivity to system changes and uncertainty.40,46
Climate change can contribute to political and social instability and, in some instances, to conflict (likely, high confidence). It impacts the operations and missions of defense, diplomacy, and development agencies critical to US national security (very likely, high confidence). The US Government, bilaterally and in collaboration with international partners, is increasingly addressing these implications through a range of diplomatic, development, and defense responses (very likely, high confidence).
Climate change exacerbates existing security challenges and risks, affecting a wide range of US national security interests.48,49,50 Climate change impacts and responses can contribute to political and social instability as well as various forms of conflict.2,49,51,52,53 Security-related concerns can also stem from the impacts of climate change on human lives and livelihoods, food and water security, biodiversity, and ecological and human health, as well as the responses to these impacts.54,55,56 Inversely, conflict can exacerbate climate-related vulnerabilities, particularly affecting women, children, and overburdened populations.57 This interplay between climate and conflict can hinder both mitigation and adaptation progress. The risk of destabilization and conflict connected to climate change has implications for US security interests distributed worldwide.
As shown in Table 17.1, the climate risks to US security interests span from local instability to geopolitical tension. In addition to the risks of instability and conflict, compounding dynamics include declining agricultural production and food security;2 recruitment and influence for extremist or violent groups;58 and declines in state capacity or legitimacy, including potential corruption, where governments cannot effectively respond to extreme weather events or long-term, chronic climate-connected impacts.59,60,61
Mobility, both planned and forced, is a common adaptation response to a changing environment, contributing to displacement and migration that primarily occurs within countries and, at times, crosses national boundaries.31,62,63 Climate change–related mobility, impacting both sending and receiving populations, is expected to increase.50 Ongoing international engagement continues around climate change and mobility, but limited international governance that provides binding protections for people crossing national borders due to climate change results in varied state and regional responses.64
As countries continue to work toward adaptation and mitigation goals, alternative climate interventions are being considered to reduce the warming effect of greenhouse gases and avoid tipping points. One category of alternative intervention is carbon dioxide removal, technical interventions to remove carbon dioxide from the atmosphere that can have impacts on food systems, biodiversity, and other systems (Chapter 32). Solar radiation modification (SRM) constitutes a variety of approaches to reduce sunlight reaching the lower atmosphere. The potential risks and benefits involving the use of SRM need to be considered relative to the risks and benefits associated with plausible trajectories of ongoing climate change not involving SRM.65 SRM represents an area of growing interest for national security given the potential for unilateral action from state and non-state actors, evolving understanding of climate and societal impacts, and limited formal or informal mechanisms of engagement.66,67 Understanding the risks and trade-offs of these alternative climate interventions is a rapidly growing field of study.
Climate change impacts are of particular concern in areas with limited resilience, unequal resource distribution, and/or weak governance structures. Unintended consequences of climate responses can also have important national security implications. For example, mitigation and adaptation efforts can unintentionally exacerbate new or existing conflicts and inequalities affecting marginalized populations.68,69 Dynamics accompanying an energy transition such as price variability, loss of employment in the fossil fuel sector, and stranded assets for petroleum-producing countries may also contribute to internal protest and reduced support for strengthening international climate change mitigation efforts.70 International climate change responses are shifting geostrategic and regional interests and priorities. These dynamics include competition for minerals and metals critical for mitigation and renewable energy.71,72 Figure 17.2 displays the source of these materials, many of which are sourced outside the United States; however, note that China controls much of the market for mining and processing of many of these minerals and metals, leading to heavy dependence on China for resources critical for energy technologies. Moreover, the extraction and processing of these necessary inputs can heighten local ecological, political, and justice tensions.73 Interests across the Arctic have also come under greater scrutiny as rapid warming opens up natural resource extraction possibilities, new sea transport routes, emergency response expectations in the event of accidents, and increased military activity, particularly by Russia (Chapter 29).
Countries may also leverage climate change mitigation and adaptation policies to gain influence and foster new coalitions. Each country will experience a wide variety of climate-related security concerns that can generate new interests or alter existing interests within bilateral relationships.50,61 For example, climate change impacts can disrupt global supply chains, such as those for food, energy, and critical minerals.72 These disruptions affect US national security interests, particularly when occurring in tandem with responses to health, economic, and political crises such as those presented by COVID-19 and the war in Ukraine.
US national security, diplomatic, and development agencies are responding to the national security impacts of climate change and competing with other countries in these engagements.76,77,78,79 Climate change impacts and responses have implications for defense, diplomacy, and development portfolios, including the climate-altered operational environment, US military and civilian infrastructure in partner countries, and humanitarian response.49,79,80 Government responses include developing climate mitigation and adaptation plans; adapting operations, assessments, and infrastructure to be more resilient; building adaptive capacity and resilience to reduce future risk; and addressing threats and opportunities with a range of defense, diplomacy, and development approaches.81,82,83 Within this geopolitical context, countries cooperate and compete and may try to take advantage of climate change impacts to gain influence.49
A number of multilateral forums (such as the UN Security Council, UN General Assembly, UN Environment Programme, European Union, North Atlantic Treaty Organization, African Union, and Organization for Security and Co-operation in Europe) recognize the interdependent nature of climate change impacts and their implications for national and regional security and have initiated collaborative responses to address transboundary risks.
Defense, diplomatic, and development institutions face increasing operations and emergency response expectations, often arising in new regions that are geopolitically relevant for US interests, as well as increasing requests for humanitarian support worldwide.76,84 To ensure continuity of operations around the world, adaptation measures ensuring reliable and functional host country infrastructure and services at risk from climate change are a priority for US federal agencies. With international partners, the US Government is increasingly addressing climate-related risks to US national security through a wide range of responses. Assessing and responding to climate-related national security risks relies on the exchange of quality-assured information across global, regional, national, and local scales (see Box 17.1).
The physical impacts of climate change are increasingly affecting global and regional economic growth (very likely, high confidence). These impacts have important implications for US economic, trade, and investment interests (likely, medium confidence). Global mitigation and adaptation responses by governments and businesses will likewise impact US economic interests, presenting both risks and potential opportunities for the US economy (likely, medium confidence). Public- and private-sector institutional, regulatory, financial, and market-based frameworks for climate mitigation and adaptation will influence these risks and opportunities (likely, medium confidence).
The impacts of climate change on global ecosystems, agriculture, human settlements, infrastructure, health, and migration translate into economic impacts that vary across regions and countries, as well as the extent to which effective adaptation measures are undertaken (Ch. 19).2,85,86 Losses from climate-influenced disasters are globally widespread and growing, including from a wider range of climate-related events, such as wildfires and floods (Figure 17.3).87,88,89 Although climate change has played a significant role in these trends, consensus is lacking on the extent to which increased losses are attributable to climate change versus other factors.90,91
In addition to acute impacts, slow-onset climate impacts such as biodiversity loss and the effects of rising temperatures on health and agriculture in vulnerable regions, as well as nonlinear climate risks (tipping points), will affect economic growth.92,93 A growing body of literature identifies sea level rise (SLR) as a key driver of economic impacts from climate change, with one study estimating global economy-wide GDP losses as high as 4% by 2100 from SLR-related coastal flooding if no adaptation measures are undertaken.94
Climate change impacts beyond US borders expose US economic, trade, and investment interests to risk because these interests are highly integrated in the global economy (Focus on Risks to Supply Chains; Ch. 19). For example, US foreign direct investment overseas and the value of exports and imports reached record levels in 2022.95,96,97
Although research relating climate change impacts outside of the US to direct impacts on US trade and investment interests is sparse, analyses suggest several risks to which US overseas investments and trade will be exposed, such as reduced asset values, greater risks of loan default, disincentives for new investments, and trade implications. For example, vulnerable countries face prolonged economic disruption from climate-related disasters, including loss of income and consumption and a higher risk of sovereign debt default.98,99 Economic shocks in foreign countries are expected to reduce US agricultural exports, production, and farm income (Ch. 11).100 According to one study, global temperature increases of 3.6°–5.76°F (2.0°–3.2°C) would reduce midcentury GDP in the US, Canada, and the United Kingdom by 6%–9%, compared to growth without climate change.101
Global climate responses, including policy choices and market responses, present both risks and opportunities for US economic interests as other countries transition toward low-emissions, climate-resilient economies.86,102 Transition risks include potential job losses, stranded assets, energy price increases, and potential negative impacts on the global financial system.103 Adaptation responses that restrict development in risk-prone areas could limit options for US investors or leave existing assets exposed.104
The global transition, including increased global financing for mitigation and adaptation (Figure 17.4), will also generate innovation, trade, and investment opportunities for US firms (Ch. 19).105,106,107 Opportunities for innovation and investment include low-carbon energy and carbon capture; transport and infrastructure; adaptation technologies in water, agriculture, health, and other sectors; resilient supply chains; and climate services.108
Governments and financial institutions are increasingly using blended finance, green bonds (fixed-income debt instruments that enable investments in climate change mitigation and adaptation), guarantees, and grants to unlock private-sector climate-related investment, including in areas such as land use, reforestation, and adaptation.109,110 Multistakeholder partnerships are also harnessing market forces to reduce emissions, such as by encouraging deforestation-free commodity supply chains.111 Workforce development and youth engagement programs are being implemented to prepare economies for the transition to climate-resilient development.112,113
Evolving regulatory and market frameworks and financing are important enabling conditions that will influence the effectiveness of global climate responses—including in achieving Paris Agreement climate mitigation and adaptation goals—and their impact on US economic interests.108,114,115,116 Total global financing for climate mitigation and adaptation (Figure 17.4a) grew steadily from 2011–2020 but slowed in the years just prior to the pandemic and falls short of estimated needs to meet Paris Agreement goals and avoid the worst impacts of climate change.117 Private-sector contributions increased between 2011 and 2020, although more slowly than public-sector contributions. Adaptation finance grew nearly three times faster than mitigation; however, methodologies for tracking adaptation finance are less developed than mitigation finance and subject to data gaps, particularly from the private sector.118 While important caveats apply (see Figure 17.4 metadata), US investments in the energy and transport sectors have grown steadily between 2013 and 2020, largely tracking overall global climate finance increases, including in these sectors, albeit more concentrated on domestic US rather than overseas investments (Figure 17.4b).118
Regulations and economic incentives supporting mitigation and adaptation, carbon markets, climate-related innovation, reduced deforestation, subsidy reform, and climate-related risk disclosure can spur companies, investors, and others to address climate risk (Ch. 19). Public sector policies and frameworks to incentivize greater ambition on mitigation include the 2022 US Inflation Reduction Act (IRA) and the EU’s Carbon Border Adjustment Mechanism (CBAM), adopted in May 2023. The CBAM may impose costs for US exporters to Europe and spark retaliatory measures by others, with spillover impacts for US exporters to other regions.119,120 Although domestically oriented, the IRA may spur investment by US companies in renewable energy and other technologies that could be applied to international markets.
Investors and companies increasingly view climate change mitigation as a business necessity and an opportunity.108,121,122,123 From November 2020 to November 2021, the number of companies worldwide committing to reducing their carbon footprint to “net zero” through emissions reductions, carbon capture, and emissions offsets by 2050 or sooner had grown from 30 to more than 450, and the value of assets represented multiplied 26 times.124
The value of global carbon offset trading quadrupled from 2018 to 2021.125 The Paris Agreement Article 6 rule book, adopted in 2021, creates global norms for government carbon trading and is expected to inform private transactions.126,127,128 A maturing carbon offset market is projected to grow 15-fold by 2030 and 100-fold by 2050, presenting opportunities for US firms to meet mitigation goals through overseas investments and the potential to generate resources to support local adaptation measures.129,130,131,132 There remain concerns that carbon trading could shift burdens onto developing countries, vulnerable communities, and future generations.133,134
A growing number of investors and asset owners have committed to evaluate and disclose climate risks. As of September 2022, 3,400 organizations from 95 countries have supported the Task Force on Climate-Related Financial Disclosures, representing nearly all economic sectors.135 Banks, insurance companies, and pension regulators are focusing on climate-related risks.136,137,138 The US Securities and Exchange Commission has proposed mandatory climate financial risk disclosure, paralleling similar actions by the United Kingdom and others.139,140
Despite growing corporate interest in addressing climate change, implementation lags behind commitments to climate risk disclosure and net-zero goals. Pressure is growing to convert these commitments into credible measurable actions, including through science-based targets.113,141,142,143,144 Small- and medium-sized enterprises may face challenges navigating complex reporting standards, which could impact their competitiveness and access to financing.145 Increased climate risk disclosure may increase costs and discourage US investment in vulnerable areas.146
Despite historic challenges, increased awareness of risks and market opportunities has begun to generate interest in private investment in adaptation. Private-sector adaptation investment has begun to be tracked alongside public climate adaptation finance, although less than $500 million was identified in 2021.117 Institutional investors have begun to develop frameworks for investing in climate adaptation and resilience opportunities.147 The Adaptation Solutions Taxonomy, peer-reviewed and released in 2020, identifies companies supporting adaptation and climate resilience solutions.148 The first private investment fund secured $185 million for climate resilience and adaptation technologies in 2022.149
While government regulations, expenditures, and market-driven climate responses are key to creating enabling environments for climate responses, they can also increase corruption risks, which in turn can undermine business efficiency, frustrate the effectiveness of climate responses, and exacerbate insecurity or poor governance.59,60 Thus, enabling environments to ensure transparent, accountable, and participatory climate responses may impact the balance of risks and opportunities for US businesses and economic interests.150,151,152
Climate change undermines the world’s ability to develop sustainably, reverses development gains, and exacerbates inequities (very likely, high confidence). Climate finance is increasing, but global flows continue to fall short of needs (likely, high confidence). Accelerated deployment of adaptation and mitigation action at scale can yield substantial benefits for sustainable development (likely, medium confidence). Climate action is most effective when co-developed and grounded in equity, local ownership, and inclusive governance (likely, medium confidence).
The impacts of climate change are globally pervasive, touching all aspects of human, built, and natural systems, including food security, poverty, health, water, infrastructure, and education, among others. Climate change is a risk multiplier in the face of existing development challenges, such as a rapidly growing population base; increased migration, particularly to urban centers, and displacement; increased food insecurity; and rising energy demands. These development challenges are also hampered by reductions in the capacity of natural resources and landscapes to buffer against increased risks, an inability of lifeline services to keep pace with needs, limited economic diversification, low educational levels, and weak institutions to manage these changes.153 In conjunction with these and other factors (Figures 17.1, 17.2), climate change undermines sustainable development, reversing the significant development gains made in recent decades.154,155,156,157 These challenges highlight the need to take into account the impacts of climate in development trajectories in order to inform mitigation and adaptation response to achieve sustainable development.158,159,160
Globally, an estimated 26 million people are falling into poverty every year due to extreme weather events such as floods and droughts, and projections point to millions more that could be pushed into poverty by midcentury due to climate change.153,161 Climate change impacts fall disproportionately on low-income countries and on marginalized and underrepresented populations, which have fewer resources to adapt. Figure 17.5 shows the differential mortality risks from climate change around the world, which results in unequal distribution of risk between and within countries. Limited resources, response capacities, and geophysical and socioeconomic constraints can reduce the feasibility of adaptation.162,163,164,165 In some contexts, impacts will be beyond the ability of communities to adapt (Ch. 31).2 This raises equity concerns, particularly given the relatively small greenhouse gas contributions of many low-income populations.166,167
Despite growing climate financing, global finance flows continue to fall short of mitigation and adaptation goals and needs.2,117 To avoid the most dangerous impacts of climate change, annual international climate finance flows in support of adaptation and mitigation efforts would need to increase by 3 to 6 times from current levels by 2030.2 Even if mitigation finance goals were met, adaptation finance and the resulting percentage of climate finance toward adaptation would need to increase as well.169 Adaptation costs for developing countries alone are projected to be $140–$300 billion annually by 2030 and $280–$500 billion by 2050 (dollar year not reported), and some estimates go further to propose a doubling or tripling every few years.107 To date, most adaptation investments have been fragmented, project-based, small-scale, incremental, sector-specific, and more focused on near-term risks and planning.170 Achieving mitigation and adaptation goals requires alignment of domestic, international, public, and private investment, practices, and business models.117
The increasing debt burden many countries incur to manage climate risks and restore economies and livelihoods after extreme events represents a growing obstacle to sustainable development.153,171 Although large disasters make headlines, globally the cumulative losses from small-scale recurring disasters account for a larger portion of economic losses and erode community resilience.2 Proactive investments can help safeguard against budget restructuring or reallocations as extreme events become more frequent. For example, investments in early warning systems, flood inundation models, and insurance schemes could have offered protection and limited the long-term effect of the recent floods in Pakistan, where development funds were diverted to disaster response.
Adaptation investments can be affordable, with benefits that far exceed costs not just in terms of financial costs and benefits but also in reduced humanitarian spending, avoided asset losses, and lives and livelihoods saved.2 The net benefits of investing in mitigation and adaptation include reduced future losses, positive economic outcomes, and social and environmental benefits. Mitigation benefits are expected to exceed costs, even without comprehensive accounting for avoided losses, reduced adaptation needs, and co-benefits, and higher near-term investments are projected to lead to long-term economic gains.2 The benefits of investing in adaptation across a range of sectors are significant, spanning from $2–$13 for each $1 invested, with some of the higher ranges being associated with investments in infrastructure resilience, early warning and response, and disaster risk management.172,173,174 Conversely, estimates of the costs of inaction range from a 7% to 14% reduction in global GDP.101,175
There is evidence of effective mitigation and adaptation options that are feasible to achieve at scale in specific contexts.2 Accelerated response to climate change can shift development pathways toward increased sustainable development outcomes despite climate change trajectories. Climate-resilient development efforts are enabled by responses that span policy, diplomacy, public and private investment, and the development and humanitarian assistance domains.2,176,177,178,179 Increasingly affordable and accessible low-emissions technologies support shifting away from fossil fuels to limit warming.2 Policy interventions at multiple levels, especially those involving ambitious near-term mitigation targets from current and projected major emitters, can minimize potential for overshooting 1.5°C (2.7°F) warming.2 Adaptation efforts can reduce disruptions due to shocks and stressors and help countries and people accelerate responsive solutions, aligned with local needs and opportunities, leading to sustainable outcomes, especially for vulnerable populations.2,180 Internationally, increased coherence and coordination among humanitarian, peace-building, resilience-building, and development can help address convergent risks and opportunities.181 Participation in international and transboundary climate efforts is shown to result in national and subnational government and civil society action.169
Integrated approaches to mitigation and adaptation can further amplify co-benefits of actions.182 For example, mangrove conservation and restoration, one of many nature-based solutions with mitigation and adaptation outcomes, can minimize the risk of coastal flooding, reduce greenhouse gas emissions, sequester carbon, and contribute to broader sustainable development benefits related to food security and nutrition, economic prosperity, marine and coastal protection, and natural habitat and biodiversity.4 Response options also have trade-offs with each other and with various sustainable development goals due to the complex interconnectivity of climate and non-climate risk (Ch. 31). Increased attention to adverse impacts of responses and development pathways can help avoid lock-in of emissions trajectories, maladaptation, and exacerbated inequalities.2 Further, global momentum and evidence are growing on approaches to accelerate transformative climate actions that embed systems thinking and innovation to facilitate more resilient development pathways.183,184,185
Inclusive governance favoring locally led, collaboratively developed responses can strengthen the potential for enabling effective and equitable climate-resilient development outcomes at scale.26,185 Meaningful engagement of affected groups (including those historically underrepresented and/or marginalized) and the co-development of information and solutions build capacity and increase support for long-term sustainable and equitable response outcomes (KMs 31.1, 32.2).186,187 Decision-relevant information, and the capacity to use it in novel ways, underpins effective responses.188,189,190 This information may be global or local and derived from diverse knowledge sources, including the scientific community as well as Traditional Knowledge. Governance and decision-making processes that integrate climate into substantial development efforts and account for the above factors can minimize trade-offs and adverse impacts and result in climate action that advances US interests in broader sustainable development outcomes.185
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This chapter focuses on the implications of international impacts of climate change on US interests. It does not address or summarize all international impacts of climate change. The topics in the chapter—interdependent climate-related risks; national security; economics, investment, and trade; sustainable development; and climate services—were selected because they represent critical interests that are being affected by climate impacts outside of US borders. Climate effects to these interest areas are context specific and are pervasive across the world. The chapter is limited in terms of providing specific detail due primarily to space constraints and limited literature that specifically addresses climate impacts to US interests.
The authors agree that this points to the lack of a sufficiently timely, policy-oriented, and geographically detailed US Government scientific assessment of climate change outside the US. In addition, current literature does not adequately address or provide evidence on the wide range of response options that could be taken to mitigate impacts. Therefore, US national security and international policymakers and analysts must rely on IPCC assessments, existing academic literature, in-house analysis, or ad hoc contracted studies, which are suboptimal or potentially inconsistent.
Chapter leadership sought an author team that could bring diverse experience, expertise, and perspectives. Care was taken to ensure that the team included both early-career and senior professionals from across government, academia, and the private sector who came from varying geographic areas and personal backgrounds. The authors were selected from the list of individuals who responded to the Federal Register Notice or otherwise directly contacted the US Global Change Research Program (USGCRP) to volunteer. Technical contributors were onboarded to conduct an extensive literature review to further identify any dissensions and help reconcile different inputs. Technical contributors also supported design and development of selected figures. The writing team engaged in conference calls starting in September 2021, and calls continued on a regular basis to discuss content, writing, and technical and logistical issues related to the chapter. The NOAA Technical Support Unit staff joined some of these regular conference calls. Subsets of chapter authors also held conference calls on literature, content, and writing on different sections of the chapter.
Public feedback was sought via Federal Register Notices and a public engagement workshop. During the workshop, the USGCRP and chapter authors shared information about the progress to date of the chapter and sought input from stakeholders to help inform further development of the chapter, as well as to raise general awareness of the process and timeline for the Fifth National Climate Assessment (NCA5).
Read about Confidence and Likelihood
The literature base on climate change and systemic, interdependent risk has grown significantly since the publication of the Fourth National Climate Assessment (NCA4) in 2018, which looked into transboundary climate risk—that is, how climate impacts in neighboring countries affect US interests. However, the literature on global systemic risks cannot yet be considered expansive; it has evolved from a focus on the financial sector and has more recently increased—not as a result of climate shocks but rather due to recent supply chain disruptions and the observed ripple effects of COVID-19, which put that interconnectivity into stark relief. According to Li et al. (2021)19 and Simpson (2021),20 the existing literature highlights the importance of climate change as a driver of systemic risk, but there is a gap in understanding in terms of the interactions and dynamics that generate risk, the methods to support risk assessment, and the design of adaptation and mitigation responses to address complex risk. There is a lack of evidence surrounding the effectiveness of emerging systems- and scenarios-based approaches that are being designed and implemented to address complex, interdependent risk.40,46
The literature is evolving from predominantly sector- (e.g., water security, food security) or domain-based (e.g., urban areas) risk assessment toward consideration of complex, interdependent systems that can result in compounding and cascading climate impacts.
There is little available literature that focuses on broad and cascading impacts of interconnected/interdependent climate risks in relation to compounding and cascading effects on multiple US interests. Nor is there a literature base that assesses the performance of approaches and measures to address systemic, interdependent risk.
There is high confidence and it is likely that in a globally connected world, climate change impacts on US interests are multifaceted, interconnected, and frequently exacerbated by social unrest and environmental degradation. These interconnections and their ripple effects are well documented.
There is high confidence and it is likely that the scale and speed of climate-related impacts to US interests are expected to increase, due in part to underlying interdependencies and to the projected intensification of climate change. It is unequivocal that climate change is intensifying and that it will result in increased impacts across systems and value chains.
There is high confidence and it is likely that emerging systems- and scenarios-based approaches to integrative planning are being applied to account for interdependencies and competing priorities. Although these approaches have been developed and are being applied to identify risks and responses, the literature surrounding their effectiveness is less advanced.
The literature base on climate change and national security has grown significantly since NCA4, as well as in the approximately 15 years since it became a more prominent focus for scholars and practitioners.48,53 Given the significant diversity of topics and regions considered for links between climate change and national security, the literature is evolving and cannot yet be considered expansive. Some research questions for which the literature was limited and contested during the NCA4 review period have since seen significant additions and greater agreement among findings, including collaborative research efforts among large groups of scholars. An example of this convergence of findings in recent years involves questions around causal links between select climate impacts and the onset of conflict.52 Literature on other research questions, such as causal links between climate responses and conflict, is less advanced and more deductive, often based on historic responses in related issue areas. The number and diversity of US government responses to climate change and national security actions have expanded since the NCA4 review.49,50
Given the diversity of potential research topics connected to climate change and national security, a number of issue areas and geographies have limited literature using diverse methods. In some cases, data remain limited in scales and locations, which constrains the types of methods that can be utilized. In other instances, the institutional responses to climate change that may have national security implications remain in early stages and therefore do not present an evidence base that could generate research findings with the highest levels of confidence.
There is high confidence and it is likely that climate change can be a contributing factor to political and social instability and in some instances conflict. There is high confidence and it is very likely that climate change increasingly impacts the operations and missions of defense, diplomacy, and development agencies and departments critical to US national security. There is high confidence and it is very likely that defense, diplomacy, and development agencies and departments are increasingly addressing climate impacts and responses across the government. These confidence levels are based on an in-depth review of a robust body of literature drawn from numerous disciplines, as well as a growing set of US Government and international policies, programs, and assessments.
There is significant research on global and regional impacts of acute and chronic climate-mediated risks.2 There is an emerging body of literature that analyzes economic impacts of these risks on global and regional economies.85,86 However, studies that draw conclusions regarding macro-level economic impacts of climate change (e.g., Swiss Re 2021101) require assumptions regarding the cost of uncertainty that would benefit from peer review and more analysis. The most granular data on the costs of physical climate impacts pertain to acute risks, such as climate-mediated disasters, rather than chronic risks. However, there is debate among scholars on the degree to which the economic effects of acute events are attributable to climate change.90,91
Figure 17.3 reflects data reported to EM-DAT, the International Disaster Database on disaster-related events, types, and costs.191 The categorization of data within this database is dependent on how events are reported, and there may be some discrepancies in how specific events and associated losses are characterized by reporters. For example, EM-DAT captures events and quantifies losses for storm events (including tropical, extratropical, and convective storms) as well as floods (including coastal, riverine, flash, and ice-jam floods). However, EM-DAT does not provide guidance to data reporters for distinguishing flood events from storm events; as a result, damages from floods caused by storm events could potentially be reflected under either “storms” or “floods.” However, the purpose of the figure is to show overall trends in event types and damages; the potential for discrepancies in how these events and associated damages are reported in the database is not material to the overall intent of the figure.
A relatively sparse but growing body of literature analyzes economic effects of climate change on sectors or topics in which US economic interests are highly embedded, such as sovereign lending,98,99 agriculture,100,192,193,194 and migration.195 These studies offer insights from which expected economic impacts on US economics, trade, and investment may be inferred; however, they generally fall short of attempting to quantify isolated impacts to US economic interests.
A growing body of literature from think tanks, consultants, multistakeholder organizations, and institutional sources provides empirical evidence of trends and practices regarding economic risks and opportunities and participation of private-sector interests in climate responses. The literature available in peer-reviewed scientific journals is less extensive than reports and studies available from non-peer-reviewed sources but is growing. Recent literature addresses the impact of corruption on climate responses. However, the most comprehensive and authoritative assessment of corruption risks posed by climate responses derives from a 2011 study.152
Literature estimating the global and regional economic impacts of physical climate risks, as well as of mitigation and adaptation response choices, is evolving. In addition to more granular analysis of these impacts across different risk categories, gaps in the literature include analysis of how economic impacts outside the US spill over into impacts on US economic, trade, and investment interests. Greater exploration of how policy, regulatory, market, and financial enabling environments mitigate or exacerbate economic, trade, and finance impacts—both at the global and regional levels as well as for US interests—would be valuable. The interrelationship of corruption and climate responses is a topic of emerging relevance that would benefit from updated research and analysis.
There is high confidence and it is very likely that the physical impacts of climate change are increasingly affecting economic growth at global and regional levels outside of the United States.
There is less authoritative analysis of how these global and regional economic impacts translate into impacts on US economic, trade, and investment interests. Studies of specific areas of economic impact in which US economic interests are highly embedded suggest likely implications for US interests, which can be inferred with medium confidence.
Similarly, while it is clear that responses by governments and the private sector to climate change will affect the economic impacts of climate change globally and in specific regions and that these responses are expected to translate into both risks and opportunities for US economic, trade, and investment interests, there is a lack of precise analysis attempting to quantify these effects. Consequently, these impacts are assessed as likely and with medium confidence.
An important mediator of these impacts is the quality and effectiveness of policy, regulatory, market, and financial frameworks that governments and private institutions develop to enable climate change mitigation and adaptation responses. The impact of these enabling environments on US economic, trade, and investment interests is assessed as likely and with medium confidence.
These confidence levels are based on empirical observation of trends and developments, supplemented with scholarly analysis and significant data relevant to business practice and sentiment reflected in the copious trade literature.
The literature base on climate change, sustainable development, and disaster risk reduction and recovery has grown since NCA4. The literature base is expansive given the diversity of topics, and it is further evolving. Some research questions where the literature was limited and contested during the NCA4 review period have seen significant additions and greater agreement among findings. An example of this convergence can be found in the improved understanding of the importance of interconnectivity of climate and non-climatic impacts on populations and potential effective response options.185 There has been an increase in literature on the social and economic impacts of climate change and on the implications for poverty and exacerbating inequality.153,161 Likewise, increasing evidence not only points to the growing need for climate finance and aligning investments for both mitigation and adaptation but also recognizes that while climate finance is increasing, it is not matching or keeping pace with this need. The evidence base on response options has greatly expanded, and the authors have focused on emerging trends and cross-cutting efforts instead of attempting to represent the vast literature on specific response options within various sectors.
Given the diversity of potential research topics connected to climate change, sustainable development, and disaster risk reduction and recovery, there is not consistent depth of literature across research topics, geographies, levels (from local to international), and sectors. In some cases, data remain limited in scales and locations, which constrains the types of methods that can be utilized. In other instances, the nature, extent, and effectiveness of responses relative to this section remain in early stages and therefore do not present an evidence base that could generate research findings with the highest levels of confidence. Additionally, the evidence base on the costs and benefits of implementing proactive adaptation strategies is ample but fragmented and very context dependent.
There is high confidence and it is very likely that climate change undermines the world’s ability to develop sustainably, reverses development gains, and exacerbates inequities. Climate change is threatening achievability of the 2030 Sustainable Development Goals, and impacts are very likely falling disproportionately on poor, marginalized, and underrepresented populations, and on developing countries in particular, raising equity concerns given that these individuals and countries contributed least to climate change.
There is high confidence and it is likely that climate finance is increasing, but global flows continue to fall short of needs. There is a significant literature base to support the statements that climate finance is growing but not keeping pace with current needs and that proactive investment is more cost effective than reactive investments.
There is less analysis and evidence regarding the benefits of large-scale mitigation and adaptation action at scale, leading to medium confidence and an assessment of likely that accelerated deployment of adaptation and mitigation action at scale can yield substantial benefits for sustainable development.
There is medium confidence and it is likely that climate action is most effective when co-developed and grounded in equity, local ownership, and inclusive governance.
