Climate change and California sustainability—Challenges and solutions

Abstract

Environmental sustainability (1) can be defined as “meeting the resource and services needs of current and future generations without compromising the health of the ecosystems that provide them” (2). Climate change is posing significant challenges to already challenging environmental sustainability globally (3), often by exacerbating existing problems. By the end of the century, the State of California is expected to experience average temperatures that are approximately 3° to 5° C warmer than historical means and sea level rise of perhaps as much as 300 cm (4) (Fig. 1). Even in the absence of climate change, California faces a plethora of sustainability imperatives and challenges. California is the state with the 3rd largest land area (424,000 km2), 12% of the US population (39.5 M), and 15% of US Gross Domestic Product (GDP) (if California were a country, it would arguably be the world’s 4th or 5th largest economy). The population of the State is the second most diverse in the United States and includes the largest population of Indigenous peoples (5). An economic and innovation powerhouse with a GDP of $3.7 trillion (6), the State also has one of the highest poverty rates in the nation, with an average of about 6 million people living at or below the supplemental poverty line (7), and faces a grave housing crisis that extends into middle-class households (8). Fig. 1. Increases in California’s annual average air temperatures, global sea level, California‘s annual area burned by wildfires, and California’s population between 1980 and 2020. Data from National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information, Climate at a Glance: Statewide Time Series, https://www.ncdc.noaa.gov/cag/. US Environmental Protection Agency (EPA) Climate Change Indicators https://www.epa.gov/climate-indicators/climate-change-indicators-sea-level; CAL FIRE 2021 https://www.fire.ca.gov/stats-events/; US Census https://www.census.gov/programs-surveys/popest/data/tables.html and Macrotrends.net https://www.macrotrends.net/states/california/population. Maps of Climate Model Intercomparison Project (CMIP6) All Model Ensemble projected annual temperature anomalies for 2079 to 2999 versus the 1985 to 2014 historical period (data and mapping application from NOAA Climate Change Portal: CMIP6 https://psl.noaa.gov/ipcc/cmip6/). SSP2-4.5 is an intermediate carbon emissions scenario, and SSP5-8.5 is the highest emissions scenario. The SSP5-8.5 scenario and associated projection of future climate is controversial, but most closely matches recent historical emissions trajectories (9). California possesses a rich and heterogeneous environment. The State is typified by a distinctive “Mediterranean-type climate” (winter precipitation, warm dry summers). While large areas share a relatively arid climate with much of southwestern North America, the northwestern coast supports temperate rainforest. Regionally variable climate and complex topography and hydrology, with mountain ranges surrounding central and coastal valleys, produce a wide range of habitats. These characteristics have made the region an engine of biological diversity and endemism (10). The environment has also promoted a diverse agricultural basis and encouraged urban development (8, 11), helping to fuel population growth. The development of the State, coupled with its climate and diverse environments, has also raised substantial sustainability challenges in terms of biodiversity, water resources, and wildfires. There are now 287 rare, endangered or threatened plant species and 178 listed animal species in the State (12, 13). The 21st century has been typified by droughts that have severely impacted water resources for ecological functioning and uses such as irrigation (14). The annual area burned by wildfires has been on a significant upward trend, with over 1.6 million ha consumed in 2020 (15). The challenges posed to California sustainability by climate change should not be seen as distant threats; they are unfolding today (Fig. 1). Anthropogenic greenhouse gas impacts on climate have been building over the past century, and there is evidence of a global scale regime shift in response to this commencing in the 1980s (16) that is also apparent in California (17). Focusing on the past four decades, California has experienced statistically significant increases in air temperature, sea level, and annual area burned by wildfires (Fig. 1). At the same time, the population of California has increased from approximately 24 million to almost 40 million people (Fig. 1). Aside from increasing air temperatures, climate change–driven trends seen in California include increasing heat waves (18), vapor pressure deficits (19), hot droughts (20 –22), decreased snowpack, and earlier Spring runoff (23). Terrestrial ecological effects of this include widespread browning of some vegetative landcover classes due to moisture stress, pathogens, and fires (24 –26). Sea level rise is threatening coastal marshes and listed species (27 –29), California coastal systems have experienced increases in sea surface temperatures (17). Particularly warm conditions, referred to as marine heat waves, during the period 2014 to 2018 were associated with marine mammal mortality events, kelp die-off, latitudinal range shifts in marine species, and negative impacts on fisheries (30). Currently, climate change projections for California under a range of greenhouse gas emissions scenarios predict further terrestrial and marine temperature increases (Fig. 1), increased vapor pressure deficits, decreasing snowpack (4), and relatively drier conditions for plant growth and water supply because of greater climate water deficit (31), greater relative humidity related heat waves in populated coastal regions and lower humidity related such events in the southern inland (18, 32), as well as greater climate variability and extremes (e.g., refs. 33 and 34). Greater rates of nighttime than daytime warming may affect everything from runoff and crop yield to human health (35 –37). Seasonal temperature and precipitation patterns affect regional hydrology with impacts on water supplies (21) that depend heavily on spring snowmelt from snowpack in the mountains (23). Annual area burned by wildfires is projected to increase significantly in response to the hotter and drier climate and in turn will also change the vegetation and fuels (38). The magnitude of the projected increase will generally increase inland (Fig. 1) across this topographically and climatically heterogeneous state with knock-on effects on ecosystems, disturbance regimes, water, food, and people. The State’s population is predicted to reach about 44 million people by 2050 (39). The potential of climate change to exacerbate the sustainability challenges for California’s ecosystems and large population is clear. The magnitude of projected impacts is highly dependent on greenhouse gas emissions scenarios used to drive climate models and this produces complicating uncertainties (Fig. 1). The only way to significantly mitigate impacts is to reduce emissions on a global scale. In light of challenges to environmental and economic sustainability posed by climate change, the State government has enacted proactive climate change mitigation and adaptation legislation and policies, notably the California Global Warming Solutions Act of 2006 (Assembly Bill 32) aimed at reducing greenhouse gas emissions (40). California is one of the least greenhouse gas–intensive states in the country, and its climate change mitigation policies have built on its legacy of air quality and energy efficiency programs from the 1970s and 80s that developed technical and legal expertise among state agencies (41). While arguably the world’s most ambitious policy to tackle emissions (42), AB 32 was also challenged by environmental and social justice advocates for its emphasis on a “cap and trade” approach allowing emitters to use out-of-state carbon offsets rather than reducing emissions, whereas the harm caused by ‘conventional’ air pollution associated with CO2 emissions disproportionately affects poor communities of color, and mitigation using offsets does not benefit those communities. Furthermore, the negative effects of climate change also disproportionately affect these communities. Subsequent legislation and policies have emphasized environmental justice so that the benefits of mitigation, adaptation, and decarbonization include focus on disadvantaged communities (43, 44). California continues to enact a wide-ranging set of actions, policies, and laws on its avowed path to zero carbon emissions by 2045 (45), from regional vehicle emissions and green building standards to land use planning and nature conservation (41, 46, 47). As we began preparing this Special Feature in 2023, young people in Montana had just won a lawsuit ruling that their state’s agencies were violating their constitutional right to a clean and healthful environment by permitting fossil fuel development without considering its effect on the climate (48), northern hemisphere summer was the hottest on record (49), and in September the State of California brought a lawsuit against the five biggest oil companies and the American Petroleum Institute for misleading the public for decades, knowing since the 1950s that their products caused harmful climate change but denying it. The lawsuit states that climate change has cost the State tens of billions of dollars and the oil companies should stop emitting and pay for the harms they have caused (50). The scientific community has well established that climate change is occurring globally, and the impacts will increase over the 21st century. It is time to increase focus on the specific regional, sectoral, and societal sustainability impacts of climate change and the potential adaptability solutions and their cobenefits. That is our goal here. In this Special Feature, we have invited experts in nine climate change–impacted areas of concern—environmental justice, Indigenous ecocultural stewardship, terrestrial ecosystems, freshwater ecosystems, marine and coastal ecosystems, wildland fire regimes, agriculture, urban systems, and human health—to address the following questions: What are the most significant challenges, the current impacts and the future impacts of climate change to California’s sustainability in your domain? What are potential solutions (mitigation, adaptation) and do they address equitable climate adaptation? What lessons can be generalized to other regions that share some of California’s socioeconomic and biophysical features? In and of itself, California is an important region for understanding the sustainability challenges of climate-change impacts and potential solutions given its large and diverse population, economy, agriculture, and varied ecosystems. In addition, many aspects of climate adaptation in California will have broad applicability to other regions of the United States and the world. The State has often been to focus of international as well as national attention (and critique) in terms of environmental policy (51, 52). How the State fares has global implications. Below we highlight some of the important conclusions from the papers included here and identify important common messages pertinent to a holistic approach to climate change and California sustainability. Environmental Justice Sustainability efforts related to climate change will only succeed if they are recognized as being just and fair by those impacted (53). The risks of climate change—as well as fossil fuel-generated conventional air pollution—disproportionately harm Black, Indigenous, and people of color in general and low-income communities. Populations of disadvantaged peoples subject to a variety of environmental justice challenges are widely distributed in the urban and rural areas of California. Hispanics, African Americans, Indigenous Americans, Asian/Pacific Islanders, and multiracial individuals are the most likely to live in such areas (54). California is furthermore the home to 109 federally recognized tribes and many others that currently lack federal standing, whose cultures and identities are inextricably intertwined with the State’s natural environments. Yet the first peoples of the State now make up less than 2% of the population and reservations comprise a tiny fraction of the total land area (55). For Indigenous peoples and other marginalized communities, climate change and its exacerbation of environmental injustice pose a critical threat. The first two papers situate the special feature in concepts of environmental justice and Indigenous ecocultural stewardship. Activists and advocates in California have long worked to embed environmental justice principles in climate change policy (43). The first paper addresses the nexus of environmental and climate justice, the politics of a just transition, and how equity concerns came to be part of the California climate strategy. In that paper, Pastor et al. (56) point out that low-income communities and communities of color are disproportionately vulnerable to climate-change impacts. They examine what California’s experience can tell us about the assumptions and social, political, and cultural attitudes that often create conflict between community understandings of local environmental conditions and the prevailing global, top–down conceptualization of climate change. The nearly two-decades-long, often contentious, process of incorporating environmental justice and health equity principles into California’s climate change policy provides insight into such local to national-level conflicts and the potential for building coalitions among groups working on climate solutions. The experience in California shows that meaningfully including environmental justice in climate policy formulation is important in building the broad coalition needed to support it. Pastor et al. note that the lessons from California’s successes and shortcomings in addressing climate justice are important influences on the current development of federal policy. The paper by Don Hankins (57) addresses the importance of longstanding Indigenous climate resilience in California and the critical role that expanding ecocultural stewardship can play today. Climate-change impacts California’s Tribal communities and Indigenous people within the challenging nexus of histories of land and water appropriation, the redistribution and diminution of Tribal lands, and often difficult socioeconomic and environmental conditions. Hankins notes particularly the increasing challenges that fires, in addition to drought and floods, pose to socioecological health and wellbeing. Historical legacies from settler colonialism and ongoing challenges for tribal communities amplify climate change vulnerability. However, Tribal traditional ecological knowledge (TEK) can support climate resilience and cultural identity and continuity, and support Tribal member’s physical and mental health. TEK-grounded scientific practices—land, water, and especially fire stewardship, as well as ecological restoration—can be important elements in addressing some of California’s most severe climate-change impacts. Doing so at a meaningful scale not only supports Indigenous peoples and cultures but provides important contributions to the State’s environmental sustainability by drawing upon important lessons provided by TEK. However, much more work is required to recapture and communicate to future generations the full span of TEK and to effectively integrate Indigenous stewardship into the State’s sustainability institutions. Terrestrial, Freshwater, and Coastal Ecosystems As is the case throughout the world, the people of California rely on the natural environment for a multitude of ecosystem services that extend from material resources to mental health, recreation, and spiritual values. Ecosystems are affected by, and play a role in, the global climate system, and in some cases can offer climate change mitigation via nature-based solutions (58) through carbon sequestration and other means. The above-ground live carbon stock held in California ecosystems has been estimated at 850 ± 230 Tg (59). The next group of papers address climate-change impacts and sustainability with respect to California’s richly diverse terrestrial, aquatic, and coastal/marine ecosystems. Fire is an important force in California terrestrial ecosystems and often spreads into developed areas exacting significant costs. This important topic is covered here in a separate paper. Linkages between terrestrial, aquatic, and marine ecosystems via flows of water, nutrients, and organisms mean that climate-change impacts on any one of these systems, as well as solutions, cannot be viewed in isolation. Harrison et al. (46) urge that California, faced with many complex threats that climate change poses to terrestrial ecosystems, uses an understanding of these threats to shape new ecological sustainability approaches. California’s heterogeneous and tectonically active landscape supports some of the richest terrestrial biodiversity of any temperate-zone region globally, where climate-change impacts on terrestrial ecosystems are particularly strong in the form of increasing severe droughts and wildfires, interacting with other stressors including invasive species, habitat fragmentation, and forest pathogens to affect biodiversity patterns and ecological processes. The authors provide an analysis of regional biodiversity hotspots and their exposure to climate change, and a specific recounting of the increasing threats posed by fire and renewable energy development on environmentally sensitive lands. California is centering a commitment to protecting biodiversity in its climate change adaptation plans and in its efforts to mitigate the adverse impacts of renewable energy on biodiversity. On the other hand, new approaches to managing fire are particularly challenging from a policy standpoint and desperately needed. Harrison et al. make the case that California is positioned in terms of remarkable biodiversity and a government committed to proactive environmental policies, to serve as a test bed and international example of strategies to sustain biodiversity in the face of climate change. They hold up the State’s commitment to the 30 × 30 plan as an example. California’s lakes, streams, rivers, and freshwater wetlands, like its terrestrial ecosystems, are many and varied, driven by the heterogeneous physical geography of the State. They are also strongly shaped by the Mediterranean-type climate that dominates in two-thirds of the State and generate a characteristic ‘hydrograph’—timing, magnitude, and high variability of water delivered—that define these freshwater ecosystems. Power et al. (47) provide case studies that illuminate the compounding effects of increasing water temperature, altered timing and magnitude of snowmelt and runoff flooding, water diversion, land use change, non-native species, sedimentation and nutrient loading, on rivers, wetlands, and mountain lakes in California. The examples illustrate the complex interactions of these stressors via food webs. Power et al. (47) stress the need for a stronger process-based understanding and predictive capability of the effect of climate and nonclimate stressors on freshwater ecosystems, encompassing climate, hydrology, and organisms and their interactions in order to protect these ecosystems and their services. However, they also note that developing mechanistic models for such complex systems will not be easy. These authors emphasize the important role of researcher-practitioner dialogue in these efforts, and offer models of successful solutions supporting healthy aquatic ecosystems including restoring quasi-natural flow regimes from reservoirs, and wetland restoration in combination with floodplain agriculture. California’s 2,000 km coastline encompasses rich and unique coastal and marine habitats. More than two-thirds of California’s people live in coastal regions and 85% of the State’s Gross Domestic Product is generated there. California’s socioeconomic sustainability depends directly and indirectly on services from these coastal and marine ecosystems that have already been degraded by human activities including development and habitat loss, degraded water quality, and overfishing. The most important effects of climate change result from extreme compounded events—accelerated sea level rise compounded with storm surge, and generally warming ocean temperatures combined with discrete marine heat waves. These phenomena are already being experienced in California in the form of coastal erosion, flooding, and disruption of marine food webs. Thorne et al. (60) propose that solutions, although they have a strong foundation in existing policy and management strategies, will need to be accelerated and scaled up, and that comanagement that includes diverse groups should be emphasized and supported by policy-relevant research. Comanagement is essential to navigating conflicts in California’s socioecological system, e.g., coastal armoring versus nature-based solutions to address sea level rise. Virtually all of California’s terrestrial ecosystems, with the exception of the warm deserts, are adapted to natural wildfire disturbance—plants and animal populations are resilient to periodic wildfire. Fire regimes—the typical frequency, severity, and size of fire disturbance—vary widely, however, from the forests of the cool, wet northwest coast to the dry shrublands of southern California. Although California, like much of the Western United States, has seen record-breaking wildfire in recent years (19), it is challenging to attribute fire regime change to climate change solely and to forecast future climate effects on fire regime, owing to the complex interactions of weather, fuel, and ignitions that drive wildfire. While weather and fuel moisture are related to climate, fuel structure and ignitions have been strongly altered by past and present land use, invasive species, and other human activities. Syphard et al. (61) consider California’s future fire landscape under climate change scenarios. Because climate and fire trends are correlated, wildfire activity is expected to increase in California in the coming decades, but climate-fire relationships vary across California. Their empirical models, trained on historical fire patterns, predicted fire probability from climate, terrain, and human infrastructure attributes. Only subregional models that accounted for the unique patterns of vegetation, climate, human infrastructure within California’s major ecological regions projected an increase in fire with climate change in most forested regions of the State, congruent with predictions from other studies. They conclude “[t]here is no one-size-fits-all prediction for fire futures in California, nor a single strategy to mitigate fire risk to people, infrastructure, and ecosystem resilience.” Agriculture California’s ecosystems are shaped by the hydroclimatology of its summer-dry, winter-rain climate. Medellin-Azuara et al. (11) describe the State’s agricultural economy—by far the largest of any in the nation—as directly dependent on services from hydroecosystems both nearby and distant, reliant on surface- and groundwater for irrigation during the dry growing season. Beginning almost a century ago, enormous water diversion projects in the western United States impounded surface water in reservoirs and moved it via intra- and interstate canals for urban and agricultural consumption—80% of consumed water going to agriculture in California. In addition to livestock, agriculture is dominated by fruit, nut, and vegetable crops including wine grapes. California creates 60% of the nation’s value in those crops, and 80% of farm revenue and employment in the State comes from them. The changing climate has affected agricultural water demand via increased evapotranspiration resulting from increased temperatures, and supply via decreased storage due to earlier snowmelt and high rainfall variability. Although fruit, tree, and vine crops are relatively high value for the water they use, water-thirsty forage crops are essential for the State’s large dairy industry, competing for water resources. Layered on California’s infamous water conflicts that historically pitted urban versus agricultural use, are contemporary environmental regulations that require water “in stream” to support healthy ecosystems and biodiversity. Sustainable agriculture in California in a changing climate thus depends on both water stewardship and cropping system adaptations that may support climate change mitigation (soil carbon sequestration) as well as climate adaptation and ecosystem services—buffering temperatures, conserving water, and supporting biodiversity including native pollinators. Urban Systems and Human Health The final two papers focus on key social components of California’s social–ecological systems, both addressing, in different ways, aspects of urban form and risks to human communities exacerbated by a changing climate. California’s cities are already facing challenges of sprawl, housing provision and affordability, transportation, water, energy, and inequality. Greenberg et al. (8) focus on the nexus of the affordable housing crisis in California, urban development in the wildland–urban interface (WUI), fire risk, and climate change. WUI is the area of greatest fire risk in the United States, fire risk that is also affected by climate change. The tremendous growth of WUI in California leads to fragmented habitat, increases in greenhouse gas emissions, and greatly increases fire risk. This paper challenges assumptions of what drives this pattern of development, suggesting that California’s extreme housing affordability crisis is a key driver. The authors posit that the State’s affordable housing crisis should be recognized as a significant urban form-related sustainability challenge that California is already facing, one that will exacerbate climate impacts and sustainability challenges in the coming years. They argue that expanding access to affordable urban housing is essential for effectively addressing WUI-related climate and other environmental impacts, as well as the increasing vulnerability of growing numbers of WUI residents living in harm’s way. They conclude that “[t]o address the California climate crisis, and attendant risk of fire, drought, widening commute-sheds, and habitat fragmentation, we need research and policy that enable more Californians to live affordably in urban areas.” Like the affordable housing crisis, the health impacts likely to be exacerbated by climate change—extreme heat, extreme precipitation (both flooding and drought), wildfires, air pollution, and some infectious diseases—disproportionately affect children, the elderly, poor people, and people of color in California. Jerrett et al. (62) review climate-driven health impacts with respect to attribution, potential health burden, vulnerable populations, and adaptations. They conclude that the burden of extreme heat on human health is already substantial, likely to increase and exacerbate inequities across the State, and deserves priority for mitigation or adaptation. Expanding urban green space, cool roofs, and equitable access to air conditioning, are key adaptations. Urban green space is land covered with some type of vegetation or having natural features and is touted as addressing the climate crisis by storing carbon, mitigating the adverse health and consequences of climate-generated adverse exposures, and contributing health cobenefits. Adaptation solutions to multiple health threats involve improved infrastructure, warning and surveillance systems, and/or nature-based climate solutions. The authors emphasize health cobenefits from climate change mitigation and adaptation policy. For example, air pollution has extensive and inequitable human health impacts, and while climate-change impacts on air pollution and consequently health in California have understandably focused on fine particulate matter from massive wildfires in recent years, most air pollution results directly from fossil fuel burning, as does climate warming. Reducing carbon emissions locally mitigates climate change globally but also reduces air pollution’s health impacts locally. An Uncertain Climate Future—Climate Change and California Sustainability Highlighted in this collection of papers are opportunities for climate adaptation, mitigation, and resilience that will support California’s ecological, social, and economic sustainability. Laws and policies in California are addressing climate change mitigation, i.e., reducing greenhouse gas emissions, which will require profound transformations of where people live, their work, and how they get around in this diverse and populous state. So much is about water in the semiarid West. When planning for climate change adaptation California policymakers are concerned about water for people, agriculture, and ecosystems. Recommendations in this Special Feature regarding sustainable water use involve strengthening water management and agricultural practices to address changing precipitation patterns, while promoting farming methods that reduce greenhouse gas emissions. At the same time, instream flow is critical for rich aquatic ecosystems, and creative approaches to shifting land use (farming to floodplain) in California can address a long-standing conflict. Some climate-change impacts are known with high certainty, such as increasing temperatures and sea level rise, and while the ultimate magnitude is unknown, it is certain that there is and will be change, and that it will persist for centuries. In terms of sea level, proactive solutions to resist coastal ecosystem loss, allow those ecosystems to migrate inland, and prepare for socially equitable resilience or relocation of human communities are of the highest priority. Other impacts are more difficult to predict, for example, the effects of climate change on ecosystems and wildfire. Climate is only one of several drivers of ecosystem processes and well as wildfire regime. While ecosystem-based adaptation, such as ecological restoration, has the cobenefits of increasing ecosystem resilience and protecting biodiversity and ecosystem services, some ecological dynamics are proving to be challenging to restore at scale, such as beneficial fire. Still other impacts cannot be mitigated locally (e.g., marine and terrestrial heat waves) and solutions must address adaptation. Urban planning and public health interventions address climate risks, especially to vulnerable communities, as well as other inequities challenging California including access to affordable housing and urban green space. Environmental, social, and economic sustainability goals are interdependent, and California needs to continue to develop and implement innovative policies, regulations, and practices that are framed by a climate justice mindset, are inclusive and equitable, and based on collaborations among communities, activists, agencies, and academics. Recognizing the contributions of Indigenous ecocultural stewardship to California’s ecological diversity, and collaborations among culture bearers and entities involved in ecosystem management, grounds restoration and adaptation in a strong sense of place, and intergenerational responsibility to human and more than human kin. As the first paper in the Special Feature argued, centering environmental justice in climate change policy, and raising up the voices of constituencies who are most impacted and who have historically been excluded from policy and planning, is essential for building the broad and inclusive coalition required to successfully tackle climate change mitigation and adaptation in California, and indeed nationally and globally. Conclusions The diversity of environments, plant and animal species, and people and their communities in California presents a plethora of both climate vulnerabilities and potential sustainability strategies. Thus, the sustainability of California in the face of climate change is a truly wicked problem. The articles in this Special Feature focus on the issues and solutions that the authors deem most important within their areas of expertise. It is sobering to acknowledge that the issues that are discussed in these papers are only a subsampling of all the climate challenges faced by the State. Similarly, the solutions presented here cannot capture the full scope of potential sustainability strategies. However, from widely different topics and perspectives explored by the authors, some important linkages and commonalities that extend broadly to the sustainability of the State can be drawn. 1. The sustainability threats posed by climate change extend across all of California’s diverse natural environments and to innumerable terrestrial, freshwater, and marine species. The threats extend to human communities, impacting health, food, housing, socioeconomic activity, and culture. The economically disadvantaged, people of color and Indigenous peoples are particularly vulnerable. 2. Climate change is not acting in isolation, but is exacerbated by, and exacerbates, existing stresses upon California’s natural environments and communities. An example of such compounding effects includes the threatened loss of California’s remaining tidal wetlands to sea level rise; this ecosystem has already been greatly reduced or modified by human activity. 3. Climate-change impacts in California often propagate from one domain to another. As an example, increasing annual area burned and fire severity causes declines in water quality which further exacerbates stresses of decreased water availability and increasing water temperature in aquatic systems. Fires also serve to exacerbate the housing crisis by rendering some areas dangerous to develop. Finally, particulate matter from smoke increases health risks in urban populations already contending with increasing temperatures and declining air quality. 4. Extreme events and ecological disturbance regimes, which are a natural part of California’s climate and environments, interact with, and are often intensified by, climate change. Some of the most pronounced threats to California sustainability arise from these interactions. Fire is an important example that readily crosses from the wildland to the built environment and affects human health. Storm surges and marine heatwaves are examples from the coastal zone. Drought impacts, exacerbated by warming temperatures, are keenly felt across California’s wildland, agricultural, and built environments. 5. A range of potential adaptation and mitigation strategies can be considered to address the challenges posed to California sustainability by climate change. Uncertainties in climate change projections and environmental responses require a process of adaptive management. Success depends on national, state, and local governments being committed and proactive. Education, communication, and partnerships between researchers, practitioners, policymakers, community activists, and the public are critical to developing, gaining acceptance and implemental solutions. Climate change solutions cannot be achieved without deep consideration of their environmental justice and societal justice implications. 6. There will be environmental, economic, or societal trade-offs in implementing some sustainability strategies. Addressing California’s housing crisis, while considering limitation imposed by the fire vulnerability of WUI zones is an example. In other cases, sustainability strategies can yield positive double or triple bottom lines, an example being improved ecological resilience to fire and increased support of Indigenous culture and sovereignty through the application TEK and ecocultural land management. Given its environmental and human diversity, the lessons learned in California in terms of sustainability in the face of climate change will have relevance and impact at the national and international levels. We hope that California maintains a proactive and innovative approach to this crisis. The successes and the failures of the State will in the end be of immeasurable informative value globally.