Recent reports suggest that most of the world's commercial fisheries could collapse within decades. Although poor fisheries governance is often implicated, evaluation of solutions remains rare. Bioeconomic theory and case studies suggest that rights-based catch shares can provide individual incentives for sustainable harvest that is less prone to collapse. To test whether catch-share fishery reforms achieve these hypothetical benefits, we have compiled a global database of fisheries institutions and catch statistics in 11,135 fisheries from 1950 to 2003. Implementation of catch shares halts, and even reverses, the global trend toward widespread collapse. Institutional change has the potential for greatly altering the future of global fisheries.

The ongoing emission of greenhouse gases is triggering changes in many climate hazards that can impact humanity. We found traceable evidence for 467 pathways in which human health, water, food, economy, infrastructure, and security have been recently impacted by climate hazards such as warming, heatwaves, precipitation, drought, floods, fires, storms, sea level rise, and changes in natural land cover and ocean chemistry. By 2100, the world's population will be exposed concurrently to the equivalent of the largest magnitude in one of these hazards if greenhouse gasses are aggressively reduced or three if they are not, with some tropical coastal areas facing up to six hazards concurrently. These findings highlight that greenhouse gas emissions pose a broad threat to humanity by simultaneously intensifying many hazards that have been harmful to numerous aspects of human life.Ongoing greenhouse gas emissions are simultaneously shifting many elements of Earth's climate beyond thresholds that can impact humanity 1 . By affecting the balance between incoming solar radiation and outgoing infrared radiation, man-made greenhouse gases are increasing the Earth's energy budget ultimately leading to warming 1 . Given interconnected physics, warming can affect other aspects of the Earth's climate system 2 . For instance, by enhancing water evaporation and increasing the air's capacity to hold moisture, warming can lead to drought in commonly dry places, in turn ripening conditions for wildfires and heatwaves when heat transfer from water evaporation ceases. There are opposite responses in commonly humid places where constant evaporation leads to more precipitation, which is commonly followed by floods due to soil saturation. The oceans have the added effect of sea warming, which enhances evaporation and wind speeds, intensifying downpours and the strength of storms, whose surges can be aggravated by sea level rise resulting from the larger volume occupied by warmed water molecules and melting land ice. Other inter-related changes in the ocean include acidification as CO2 mixes with water to form carbonic acid, and reduced oxygen due to warming reducing oxygen solubility and affecting circulation patterns and the mixing of surface waters rich in oxygen with deeper oxygen-poor water. These climate hazards and their impacts on human societies occur naturally but are being nontrivially intensified by man-made greenhouse gas emissions, as demonstrated by an active research on detection and attribution (discussed under Caveats in the Methods section). With few exceptions 3 , changes in these hazards have been studied in isolation whereas impact assessments have commonly focused on specific aspects of human life. Unfortunately, the failure to integrate available information most likely underestimates the impacts of climate change because i) one hazard may be important in one place but not another, ii) strong CO2 reductions may curb some but not all hazards (See Fig. S1), and iii) not all aspects of human systems are equally challenge...

As climatic changes and human uses intensify, resource managers and other decision makers are taking actions to either avoid or respond to ecosystem tipping points, or dramatic shifts in structure and function that are often costly and hard to reverse. Evidence indicates that explicitly addressing tipping points leads to improved management outcomes. Drawing on theory and examples from marine systems, we distill a set of seven principles to guide effective management in ecosystems with tipping points, derived from the best available science. These principles are based on observations that tipping points (1) are possible everywhere, (2) are associated with intense and/or multifaceted human use, (3) may be preceded by changes in earlywarning indicators, (4) may redistribute benefits among stakeholders, (5) affect the relative costs of action and inaction, (6) suggest biologically informed management targets, and (7) often require an adaptive response to monitoring. We suggest that early action to preserve system resilience is likely more practical, affordable, and effective than late action to halt or reverse a tipping point. We articulate a conceptual approach to management focused on linking management targets to thresholds, tracking early-warning signals of ecosystem instability, and stepping up investment in monitoring and mitigation as the likelihood of dramatic ecosystem change increases. This approach can simplify and economize management by allowing decision makers to capitalize on the increasing value of precise information about threshold relationships when a system is closer to tipping or by ensuring that restoration effort is sufficient to tip a system into the desired regime.

Social networks can profoundly affect human behavior, which is the primary force driving environmental change. However, empirical evidence linking microlevel social interactions to large-scale environmental outcomes has remained scarce. Here, we leverage comprehensive data on information-sharing networks among large-scale commercial tuna fishers to examine how social networks relate to shark bycatch, a global environmental issue. We demonstrate that the tendency for fishers to primarily share information within their ethnic group creates segregated networks that are strongly correlated with shark bycatch. However, some fishers share information across ethnic lines, and examinations of their bycatch rates show that network contacts are more strongly related to fishing behaviors than ethnicity. Our findings indicate that social networks are tied to actions that can directly impact marine ecosystems, and that biases toward within-group ties may impede the diffusion of sustainable behaviors. Importantly, our analysis suggests that enhanced communication channels across segregated fisher groups could have prevented the incidental catch of over 46,000 sharks between 2008 and 2012 in a single commercial fishery.social networks | environmental outcomes | homophily | shark bycatch | sustainability

The creation of marine reserves is often controversial. For decisionmakers, trying to find compromises, an understanding of the timing, magnitude, and incidence of the costs of a reserve is critical. Understanding the costs, in turn, requires consideration of not just the direct financial costs but also the opportunity costs associated with reserves. We use a discrete choice model of commercial fishermen's behavior to examine both the short-run and long-run opportunity costs of marine reserves. Our results can help policymakers recognize the factors influencing commercial fishermen's responses to reserve proposals. More generally, we highlight the potential drivers behind the political economy of marine reserves.marine protected areas | fishing behavior | bioeconomics | metapopulation | opportunity cost M any scientists and marine conservationists are calling for increases in the number of no-take marine reserves throughout the world's oceans (1, 2). As proposals to form new reserves move forward, commercial and recreational fishermen fear the short-and long-term effects on their livelihoods from lost access to particular fishing grounds. For example, proposals to site reserves near California's Channel Islands and the Tortugas in Florida generated passionate political advocacy (3). More recently, controversy surrounding the California Marine Life Protection Act has intensified as fishermen and other stakeholders question the potential benefits and science behind proposed actions (4).Advocates for marine reserves often treat fishermen's assertions about the costs with the same skepticism that fishermen have for the stated benefits. For decisionmakers trying to find compromises between these and other stakeholders, an understanding of the costs and benefits of reserves is critical. This information is particularly relevant when reserve policies are determined through public stakeholder meetings that may be dominated by extreme rather than moderate representatives of all sides in the debate, including different parts of the fishing industry (5).When a fisherman goes fishing, he purchases fuel, bait, etc., and he also forfeits opportunities to earn income in other activities, e.g., fishing elsewhere or working on land. Understanding the responses of commercial fishermen to marine reserves requires consideration of these opportunity costs. We use an empirically established model of a commercial fishery to predict fishermen's opportunity costs both in the short and in the long run. Although many of our general findings appear in the natural resource economics literature (6-10), we highlight how these responses are driven by the way a reserve changes opportunities for fishermen: opportunities that arise in space (e.g., reserves eliminate some possible fishing grounds), in the biological domain (e.g., reserves affect the abundance of target species), and in the financial realm (e.g., reserves may alter the costs of fishing). We extend the literature by considering how these opportunities vary across fishermen with hete...