Humanity is on a deeply unsustainable trajectory. We are exceeding planetary boundaries and unlikely to meet many international sustainable development goals and global environmental targets. Until recently, there was no broadly accepted framework of interventions that could ignite the transformations needed to achieve these desired targets and goals. As a component of the IPBES Global Assessment, we conducted an iterative expert deliberation process with an extensive review of scenarios and pathways to sustainability, including the broader literature on indirect drivers, social change and sustainability transformation. We asked, what are the most important elements of pathways to sustainability? Applying a social–ecological systems lens, we identified eight priority points for intervention (leverage points) and five overarching strategic actions and priority interventions (levers), which appear to be key to societal transformation. The eight leverage points are: (1) Visions of a good life, (2) Total consumption and waste, (3) Latent values of responsibility, (4) Inequalities, (5) Justice and inclusion in conservation, (6) Externalities from trade and other telecouplings, (7) Responsible technology, innovation and investment, and (8) Education and knowledge generation and sharing. The five intertwined levers can be applied across the eight leverage points and more broadly. These include: (A) Incentives and capacity building, (B) Coordination across sectors and jurisdictions, (C) Pre‐emptive action, (D) Adaptive decision‐making and (E) Environmental law and implementation. The levers and leverage points are all non‐substitutable, and each enables others, likely leading to synergistic benefits. Transformative change towards sustainable pathways requires more than a simple scaling‐up of sustainability initiatives—it entails addressing these levers and leverage points to change the fabric of legal, political, economic and other social systems. These levers and leverage points build upon those approved within the Global Assessment's Summary for Policymakers, with the aim of enabling leaders in government, business, civil society and academia to spark transformative changes towards a more just and sustainable world. A free Plain Language Summary can be found within the Supporting Information of this article.

Many animals have the potential to discriminate nonspectral colors. For humans, purple is the clearest example of a nonspectral color. It is perceived when two color cone types in the retina (blue and red) with nonadjacent spectral sensitivity curves are predominantly stimulated. Purple is considered nonspectral because no monochromatic light (such as from a rainbow) can evoke this simultaneous stimulation. Except in primates and bees, few behavioral experiments have directly examined nonspectral color discrimination, and little is known about nonspectral color perception in animals with more than three types of color photoreceptors. Birds have four color cone types (compared to three in humans) and might perceive additional nonspectral colors such as UV+red and UV+green. Can birds discriminate nonspectral colors, and are these colors behaviorally and ecologically relevant? Here, using comprehensive behavioral experiments, we show that wild hummingbirds can discriminate a variety of nonspectral colors. We also show that hummingbirds, relative to humans, likely perceive a greater proportion of natural colors as nonspectral. Our analysis of plumage and plant spectra reveals many colors that would be perceived as nonspectral by birds but not by humans: Birds’ extra cone type allows them not just to see UV light but also to discriminate additional nonspectral colors. Our results support the idea that birds can distinguish colors throughout tetrachromatic color space and indicate that nonspectral color perception is vital for signaling and foraging. Since tetrachromacy appears to have evolved early in vertebrates, this capacity for rich nonspectral color perception is likely widespread.

Interdependent relationships among humans and nature often go overlooked, delaying better environmental, social and public health outcomes. Emerging approaches have emphasized thinking through relationships, which we call ‘relational thinking’. Threads of relational thinking have matured in areas such as anthropology and Indigenous scholarship, and interest is growing across many disciplines. Welcoming this new cadre of relational thinkers requires a more broadly accessible synthesis. Sustainability scholars have begun to overcome these barriers with high‐level overviews and broad calls to adopt relational thinking. This literature has investigated the conceptual underpinnings of relational thinking, but the concrete, empirical benefits of relational thinking for understanding human–natural systems remain obscure. Here, we introduce a wide range of accessible empirical examples to demonstrate the potential for relational thinking to illuminate diverse coupled human‐and‐natural systems. We complement these examples with an overview of the theory behind relational thinking. We use these empirical examples to argue that some conventional methods are consistent with relational thinking, particularly when accompanied by deliberation and flexibility about which relationships to target, why, and how. Read the freePlain Language Summaryfor this article on the Journal blog.

Animals achieve camouflage through a variety of mechanisms, of which background matching and disruptive coloration are likely the most common. Although many studies have investigated camouflage mechanisms using artificial stimuli and in lab experiments, less work has addressed camouflage in the wild. Here we examine egg camouflage in clutches laid by ground-nesting Snowy Plovers Charadrius nivosus and Least Terns Sternula antillarum breeding in mixed aggregations at Bahía de Ceuta, Sinaloa, Mexico. We obtained digital images of clutches laid by both species. We then calibrated the images and used custom computer software and edge detection algorithms to quantify measures related to three potential camouflage mechanisms: pattern complexity matching, disruptive effects and background color matching. Based on our image analyses, Snowy Plover clutches, in general, appeared to be more camouflaged than Least Tern clutches. Snowy Plover clutches also survived better than Least Tern clutches. Unexpectedly, variation in clutch survival was not explained by any measure of egg camouflage in either species. We conclude that measures of egg camouflage are poor predictors of clutch survival in this population. The behavior of the incubating parents may also affect clutch predation. Determining the significance of egg camouflage requires further testing using visual models and behavioral experiments.

Given the massive and growing environmental impacts of conventional agriculture, humanity needs new methods for growing food that not only meet dietary needs but also provide for multiple ecosystem functions with potential benefits to people and biodiversity. Concepts from ecology and complex adaptive systems suggest that persistent structural heterogeneity and functional diversity are key for supporting biodiversity, ecosystem services, and resilience, but these concepts have not been extensively applied in agriculture, which is still dominated by annual monocropping systems. Perennial agriculture seems to embody these ecological concepts—particularly perennial polycultures that combine a variety of long‐lived woody perennial food crops with continuous ground cover. However, our understanding of the benefits and trade‐offs of such systems compared to conventional agriculture is limited, especially in temperate climates. Here, we provide a systematic and comprehensive study of the ecological attributes of 14 woody perennial polyculture farm fields to conventional annual and hay fields in the U.S. Midwest, one of the most industrialized food‐producing regions in the world. We found that perennial fields had (1) more diverse soil fungal, invertebrate, plant, and bird communities but found no difference in soil bacterial communities; (2) less compacted soil; (3) denser ground cover; (4) more active carbon, organic carbon, and nitrogen and the same available phosphorus in the top layer of soil; and (5) more species of predatory, detritivorous, and herbivorous insects, and approximately fourfold higher abundance of herbivorous insects. Food production from the oldest half of perennial fields was only 14.7% of a regional corn/soy rotation by weight, but increased with the age of the perennial field and had high nutritional diversity. Together, these findings indicate that woody perennial polyculture fields in the U.S. Midwest are characterized by higher biodiversity and ecosystem functions than adjacent conventional fields. Woody perennial polycultures in the temperate north might play a role in the transition of agricultural landscapes toward sustaining both people and nature over the long term.

Heat waves are becoming more frequent due to climate change. Summer heat waves can be particularly deadly in cities, where temperatures are already inflated by abundant impervious, dark surfaces (i.e., the heat island effect). Urban heat waves might be ameliorated by planting and maintaining urban forests. Previous observational research has suggested that conifers may be particularly effective in cooling cities. However, the observational nature of these studies has prevented the identification of the direct and indirect mechanisms that drive this differential cooling. Here, we develop a systems dynamics representation of urban forests to model the effects of the percentage cover of either conifers or broadleaf trees on temperature. Our model includes physiological and morphological differences between conifers and broadleaf trees, and physical feedback among temperature and energy fluxes. We apply the model to a case study of Vancouver, BC, Canada. Our model suggests that in temperate rainforest cities, conifers may by 1.0 °C cooler than broadleaf trees; this differential increases to 1.2 °C when percentage tree cover increases from 17% to 22% and to 1.7 °C at 30% cover. Our model suggests that these differences are due to three key tree traits: leaf area index, leaf boundary layer resistance, and dry mass per leaf area. Creating urban forests that optimize these three variables may not only sequester CO₂ to mitigate global climate change but also be most effective at locally minimizing deadly urban heat waves.