Annual Review of Environment and Resources - Volume 48, 2023

Global agreement on 30×30 means an unprecedented last push to define how much nature will be left on the planet. At the same time that space for nature is being defined, climate change will be moving nature around. Species are now on the move to track climate change both on land and in the oceans, a process that is accelerating under dramatic new extreme events. This is an opportune time to review conservation recommendations made early in the millennium, to see how many have been taken on board over the past 20 years, and how much is left to be done to adapt to climate change as conservation pushes toward 30×30. The history of Climate Change–Integrated Conservation Strategies begins with two papers published by a group of prominent climate change biologists in 2002. The importance of including adaptation to climate change in conservation was underscored by the first estimates of extinction risk due to climate change in 2004. Subsequent literature has developed concepts such as velocity of climate change and assisted migration. Regional modeling of biodiversity change, expanding protected areas to facilitate species range movements, and managing productive landscapes to facilitate species movements are all now considered “business as usual” for conservation planning for climate change. Regional coordination of conservation efforts to ensure that species on the move are managed for climate change consistently across their range, on the other hand, is under-represented in literature and practice. Improving both theory and practice of regional coordination for climate change is an important priority for conservation now and in the future. Conservation for climate change has focused mostly on warming scenarios, but failure to act on climate change emissions reduction means that meeting Paris Agreement targets will almost certainly have to include both warming past those targets and subsequent cooling back to the target. Managing this double transition is a second critical point of emphasis for climate change biology as the world moves to 30×30.

Many challenges posed by the current Anthropocene epoch require fundamental transformations to humanity's relationships with the rest of the planet. Achieving such transformations requires that humanity improve its understanding of the current situation and enhance its ability to imagine pathways toward alternative, preferable futures. We review advances in addressing these challenges that employ systematic and structured thinking about multiple possible futures (futures-thinking). Over seven decades, especially the past two, approaches to futures-thinking have helped people from diverse backgrounds reach a common understanding of important issues, underlying causes, and pathways toward optimistic futures. A recent focus has been the stimulation of imagination to produce new options. The roles of futures-thinking in breaking unhelpful social addictions and in conflict resolution are key emerging topics. We summarize cognitive, cultural, and institutional constraints on the societal uptake of futures-thinking, concluding that none are insurmountable once understood.

Plastics are persistent and pervasive throughout the environment and have now been reported from the deepest parts of the ocean to the tops of the highest and most remote mountains. There is a body of information on the sources, degradation, and transport of plastics as well as a variety of research investigating the ecotoxicological and wider ecological consequences of plastic ingestion and accumulation. Such knowledge has been obtained with developments in field and laboratory methods for plastic identification and then well-publicized in the media and wider public communications. However, although there has been a large focus on plastic pollution within the past decade, there is plenty that we do not yet know. Even within the past five years, sources of microplastics (1 μm–5 mm) to the environment have been confirmed that had not previously been considered, for example, road paints and tire wear particles. Initial research focused on plastic in the marine environment, but understanding on the accumulation and impacts in terrestrial and freshwater environments is growing. There is a substantial lack of basic science focused on the efficiency of solutions aimed at mitigating plastic pollution. This review highlights some recent (past five years) research on plastics in the environment, including investigations in accumulation, sources, distribution, impacts, solutions and provides directions for future work.

Getting to net-zero-carbon cities while advancing well-being (W), health (H), social equity (E), and climate resilience (R) (referred to as the WHER outcomes) is critical for local and global sustainability. However, science is nascent on the linkages between zero-carbon pathways and WHER outcomes. This article presents a transboundary urban metabolism framework, rooted in seven key infrastructure and food provisioning systems, to connect urban decarbonization strategies with WHER outcomes. Applying the framework along with a literature review, we find the evidence for co-beneficial decarbonization to be strong for health; limited for well-being; uncertain for resilience; and requiring intentional design to advance equity, including distributional, procedural, and recognitional aspects. We describe the evidence base, identify key knowledge gaps, and delineate broad parameters of a new urban nexus science to enable zero-carbon urban transitions with WHER co-benefits. We highlight the need for fine-scale data encompassing all seven sectors across scales, along with multiple and multiscale climate risks, accompanied by next-generation multisector, multiscale, multioutcome nexus models.

Harmful cyanobacterial blooms (CyanoHABs) impact lakes, estuaries, and freshwater reservoirs worldwide. The duration, severity, and spread of CyanoHABs have markedly increased over the past decades and will likely continue to increase. This article addresses the universal phenomena of cyanobacterial blooms occurring in many freshwater ecosystems worldwide. Based on analysis of ecophysiological traits of bloom-forming cyanobacteria and their interactions with environmental processes, we summarize and decipher the driving forces leading to the initiation, outbreak, and persistence of the blooms. Due to the coupling effects of eutrophication, rising CO2 levels and global warming, a multidisciplinary joint research approach is critical for better understanding the CyanoHAB phenomenon and its prediction, remediation, and prevention. There is an urgent need to evaluate and guide proper use of bloom control techniques at large scales, using science-based and environmentally friendly approaches.

Fungi comprise approximately 20% of all eukaryotic species and are connected to virtually all life forms on Earth. Yet, their diversity remains contentious, their distribution elusive, and their conservation neglected. We aim to flip this situation by synthesizing current knowledge. We present a revised estimate of 2–3 million fungal species with a “best estimate” at 2.5 million. To name the unknown >90% of these by the end of this century, we propose recognition of species known only from DNA data and call for large-scale sampling campaigns. We present an updated global map of fungal richness, highlighting tropical and temperate ecoregions of high diversity. We call for further Red List assessments and enhanced management guidelines to aid fungal conservation. Given that fungi play an inseparable role in our lives and in all ecosystems, and considering the fascinating questions remaining to be answered, we argue that fungi constitute the next frontier of biodiversity research.

The few percent of soil organic carbon (SOC) among mineral components form the interface of climate, plant growth, soil biological processes, physical transport infrastructure, and chemical transformations. We explore maps, models, myths, motivation, means of implementation, and modalities for transformation. Theories of place relate geographic variation in SOC to climate, soil types, land cover, and profile depth. Process-level theories of biophysical change and socioeconomic theories of induced change explain SOC transitions that follow from land use change when a declining curve is bent and recovery toward SOC saturation starts. While the desirability of recovering from SOC deficits has been mainstreamed into climate policy, the effectiveness of proposed measures taken remains contested. Process-level requirements for transitions at plot and landscape scales remain uncertain. Expectations of policy-induced SOC transitions have to align with national cross-sectoral C accounting and be managed realistically with land users (farmers) and commodity supply chains (private sector, consumers).

Fire is an integral part of the Earth System and humans have skillfully used fire for millennia. Yet human activities are scaling up and reinforcing each other in ways that are reshaping fire patterns across the planet. We review these changes using the concept of the fire regime, which describes the timing, location, and type of fires. We then explore the consequences of fire regime changes on the biological, chemical, and physical processes that sustain life on Earth. Anthropogenic drivers such as climate change, land use, and invasive species are shifting fire regimes and creating environments unlike any humanity has previously experienced. Although human exposure to extreme wildfire events is increasing, we highlight how knowledge of fire regimes can be mobilized to achieve a wide range of goals, from reducing carbon emissions to promoting biodiversity and human well-being. A fire regime perspective is critical to navigating toward a sustainable future—a better Anthropocene.

Since the early 2000s, many private companies, public-private coalitions, and governments have committed to remove deforestation from commodity supply chains. Despite these zero-deforestation commitments (ZDCs), high rates of deforestation persist and may even be increasing. On the upside, a few region- and commodity-specific ZDCs have contributed to reductions by up to hundreds of thousands of hectares of deforestation, with mixed evidence on associated leakage. ZDCs have also spurred progress in monitoring, traceability, and awareness of deforestation. On the downside, as currently implemented, supply chain initiatives only cover a small share of tropical deforestation. Government- and company-led ZDCs are just two components of broader policy mixes aimed at reducing deforestation. To be more impactful, ZDCs needs to cover entire biomes, supply bases of companies, and export and domestic markets, with special attention not to exclude marginal producers.

Visions of planting walls of trees to block the expansion of the desert have long been promoted but never realized. The green wall myth persists today even though it is premised on outdated understandings of desertification. We review the history of the idea of green walls and focus on two sets of contemporary initiatives to assess their outcomes: peri-Saharan programs (Algeria's Green Dam and Great Green Wall in sub-Saharan Africa) and China's Three Norths Shelterbelt Program. This review reveals a mixed record of technical success with low rates of the establishment of monocultures of fast-growing trees vulnerable to disease. While there is evidence for reduced wind erosion in some areas, afforestation is also associated with reduced soil moisture and lowering of water tables. Social impacts include increased water scarcity for people and livestock in some cases, and resource enclosures that particularly work against pastoralist livelihoods.

As anthropogenic transformation of Earth's ecology accelerates, and its impacts on the sustainability of humanity and the rest of nature become more obvious, geographers and other researchers are leveraging an abundance of spatial data to map how industrialization is transforming the biosphere. This review examines the methodologies used to create such maps and how they have enhanced our understanding of how societies can abate biodiversity loss, mitigate climate change, and achieve global sustainability goals. Although there have been great advances over the past two decades in mapping industrial transformations of ecology across the planet, the field is still in its infancy. We outline future research directions to better understand anthropogenic transformation of the biosphere and the utility of integrating global maps of socioeconomic, ecological, biodiversity, and climate data to explore and inform potential pathways of human-driven social-ecological change.

Modifications to land can serve to jointly reduce risks of floods and droughts to people and to ecosystems. Whether land modifications are implemented will depend on the willingness and ability of a diversity of actors. This article reviews the state of knowledge on land modification use in areas exposed to dual hydrologic risks and the land owners, managers, and users who directly make decisions about action on lands they control. The review presents a typology of land modifications and explains how land modifications interact with the hydrological cycle to reduce risks. It then addresses the roles and perspectives of the land owners, managers, and users undertaking land modifications, summarizing theories explaining motivations for, as well as barriers to and enablers of, land modification implementation. The analysis reveals geographical differences in narratives on land modifications as well as knowledge gaps regarding variation across actors and types of land modifications.

Food demand is projected to increase significantly over the coming decades. Sustainable intensification (SI) is essential to meet this demand. SI is particularly important in smallholder systems, yet to date it remains unclear what the most promising SI strategies are to increase food production and farmer incomes at scale. We review the literature on SI to identify the most promising strategies, as manifest in replicated findings of favorable causal impacts. Adoption of improved cultivars generated the largest, most consistent, positive yield and economic outcomes. Two agroecological practices, push-pull systems and the System of Rice Intensification, also repeatedly led to large positive impacts. These strategies have considerable potential to scale to reach more than 50% of smallholder farmers who plant staple crops. Significant barriers to adoption remain, however, and identifying ways to overcome barriers to scale these successful strategies will be critical to meeting Sustainable Development Goals 1 and 2 by 2030.

Brine contains cations such as K⁺, Ca²⁺, Na⁺, Mg²⁺, Li⁺, B³⁺, Rb²⁺, and Cs²⁺, as well as anions such as SO4²⁻, Cl⁻, HCO3⁻, CO3²⁻, NO3⁻, Br⁻, and I⁻, which are valuable elements. Brines are widely distributed in salt lakes in the world's three enormous plateaus and beyond and are classified into three types: sulfate-, chloride-, and carbonate-type brines. Sulfate-type brine forms in salt lakes, whereas carbonate-type brine results from magmatic and hydrothermal activity. Chloride-type brine forms in deep basins due to the reduction and transformation of buried brine. Li in brine plays a critical role in clean energy transitions, and K in brine is important for potash production. Recently, new techniques for extracting Li from brine have been developed, and the large-scale, comprehensive development pattern of brines has formed the basis for a recycling economic model, which contributes to the efficient use of brines for potash and Li2CO3 development and CO2 emission reduction. This article reviews the genesis of brines and highlights new utilization techniques, trends, and sustainable development.

Groundwater deterioration due to enrichment with contaminants of either geogenic or anthropogenic origin has adversely affected safe water supply for drinking and irrigation, with pervasive impacts on human health and ecosystem functions. However, the spatiotemporal evolution and public health effects of groundwater quality remain unclarified, posing a grand challenge for the safe and sustainable supply of global groundwater resources. This article provides a state-of-the-art review of the complexity and dynamics of groundwater quality, as well as the impacts of various groundwater substances on human health. In particular, knowledge is growing about the health impacts of key substances ranging from nutritional elements (e.g., Ca²⁺, Mg²⁺) to pollutants (e.g., heavy metals/metalloids, persistent organic pollutants, and emerging contaminants) and, further, to pathogenic microorganisms to which the human body can be exposed through multiple patterns of groundwater use. Proliferating concerns at the same time call for enhancing science-based governance directives, economic policies, and management strategies coordinating groundwater quality. We propose that safeguarding groundwater-dependent public health needs concerted efforts in source control, cross-scale rehabilitation, and social hydrology-based groundwater governance.

Renewable electricity generation will need to be rapidly scaled to address climate change and other environmental challenges. Doing so effectively will require an understanding of resource availability. We review estimates for renewable electricity of the global technical potential, defined as the amount of electricity that could be produced with current technologies when accounting for geographical and technical limitations as well as conversion efficiencies; economic potential, which also includes cost; and feasible potential, which accounts for societal and environmental constraints. We consider utility-scale and rooftop solar photovoltaics, concentrated solar power, onshore and offshore wind, hydropower, geothermal electricity, and ocean (wave, tidal, ocean thermal energy conversion, and salinity gradient energy) technologies. We find that the reported technical potential for each energy resource ranges over several orders of magnitude across and often within technologies. Therefore, we also discuss the main factors explaining why authors find such different results. According to this review and on the basis of the most robust studies, we find that technical potentials for utility-scale solar photovoltaic, concentrated solar power, onshore wind, and offshore wind are above 100 PWh/year. Hydropower, geothermal electricity, and ocean thermal energy conversion have technical potentials above 10 PWh/year. Rooftop solar photovoltaic, wave, and tidal have technical potentials above 1 PWh/year. Salinity gradient has a technical potential above 0.1 PWh/year. The literature assessing the global economic potential of renewables, which considers the cost of each renewable resource, shows that the economic potential is higher than current and near-future electricity demand. Fewer studies have calculated the global feasible potential, which considers societal and environmental constraints. While these ranges are useful for assessing the magnitude of available energy sources, they may omit challenges for large-scale renewable portfolios.

For millennia, agriculture has been shaping landscapes on Earth. Technological change has increased agricultural productivity dramatically, especially in the past six decades, but also resulted in trade-offs such as land and soil degradation, emission of greenhouse gases (GHGs), and spreading of toxic substances. In this article we review the impacts of agriculture on the world's arable land. We start by synthesizing information on the extent of arable land and associated agricultural practices, followed by a review of the state of the art of soil health and soil carbon. We review processes of land degradation, emission of GHGs, and threats to biodiversity. To conclude, we review key social and economic aspects of arable land and identify some important concerns for the future. The article ends on a positive note describing a potential new pathway for agriculture—to gradually adopt polycultures of novel perennial grain crops.

Polarization in the United States and around the world is of growing concern. Polarization is about more than just differences in opinions in society. It occurs when groups increasingly diverge in either actual or perceived differences in opinion and can involve both disagreements about issues and negative views of other groups. Since most environmental problems are collective action problems, polarization may interfere with the kinds of deliberation and collaborations needed for effective environmental decision-making. In this review, we examine how polarization influences environmental decision-making and what strategies could be useful for preventing or reducing the negative consequences of polarization. Evidence about the extent of polarization among citizens suggests the current situation may be less severe than is sometimes assumed. The coevolution of individual views, network interactions, and social media that cause polarization is complex and subject to rapid change. However, there are interventions that seem to be effective at reducing polarization.

There are large disparities in access to green technologies between countries and among different demographic groups within countries. Unless carefully managed, the energy transition risks exacerbating some of these inequalities, for example, by burdening those who are excluded from efficient new technologies with the costs of maintaining legacy infrastructure. The energy transition will create new interdependencies between sectors—for example, between buildings, the power sector, and transportation—requiring integrated design of policies and infrastructure in different sectors. The equitable adoption of new technologies is contingent on broadening access to enabling technologies such as the Internet and payment systems. Decisionmakers must focus on new technologies that remove disparities in access to services but do not replicate current inefficiencies in providing those services (e.g., equitable access to mobility—not only to motorized personal vehicles). Data at higher resolutions and with broader coverage are needed to design equitable technology deployment strategies and evaluate their success.