Dams contribute to water security, energy supply, and flood protection but also fragment habitats of freshwater species. Yet, a global species-level assessment of dam-induced fragmentation is lacking. Here, we assessed the degree of fragmentation of the occurrence ranges of ∼10,000 lotic fish species worldwide due to ∼40,000 existing large dams and ∼3,700 additional future large hydropower dams. Per river basin, we quantified a connectivity index (CI) for each fish species by combining its occurrence range with a high-resolution hydrography and the locations of the dams. Ranges of nondiadromous fish species were more fragmented (less connected) (CI = 73 ± 28%; mean ± SD) than ranges of diadromous species (CI = 86 ± 19%). Current levels of fragmentation were highest in the United States, Europe, South Africa, India, and China. Increases in fragmentation due to future dams were especially high in the tropics, with declines in CI of ∼20 to 40 percentage points on average across the species in the Amazon, Niger, Congo, Salween, and Mekong basins. Our assessment can guide river management at multiple scales and in various domains, including strategic hydropower planning, identification of species and basins at risk, and prioritization of restoration measures, such as dam removal and construction of fish bypasses. habitat fragmentation | hydropower | river management | migratory fish | biodiversity Barbarossa et al. PNAS | February 18, 2020 | vol. 117 | no. 7 | 3649 ECOLOGY ENVIRONMENTAL SCIENCES Downloaded by guest on July 3, 2020

Electrification of passenger road transport and household heating features prominently in current and planned policy frameworks to achieve greenhouse gas emissions reduction targets. However, since electricity generation involves using fossil fuels, it is not established where and when the replacement of fossil fuel-based technologies by electric cars and heat pumps can effectively reduce overall emissions. Could electrification policy backfire by promoting their diffusion before electricity is decarbonised? Here, we analyse current and future emissions trade-offs in 59 world regions with heterogeneous households, by combining forward-looking integrated assessment model simulations with bottom-up life-cycle assessment. We show that already under current carbon intensities of electricity generation, electric cars and heat pumps are less emission-intensive than fossil fuel-based alternatives in 53 world regions, representing 95% of global transport and heating demand. Even if future enduse electrification is not matched by rapid power sector decarbonisation, it likely avoids emissions in world regions representing 94% of global demand.Policy-makers widely consider electrification a key measure for decarbonizing road transport and household heating. Combined, they generate 24% of global fuel-combustion emissions and are the two major sources of direct carbon emissions by households [1][2][3][4][5] . For passenger road transport, plug-in battery electric vehicles ('EVs') are expected to gradually replace petrol and diesel vehicles ('petrol cars'). For heating, heat pumps ('HPs') are an alternative for gas, oil and coal heating systems ('fossil boilers'). Recent policy examples aimed at such end-use electrification include announced bans of petrol car sales, financial incentives for EV and HP purchases, planned phase-outs of gas heating, and the inclusion of HPs into the European Union's renewable heating targets 1,2,[6][7][8] . The use of EVs and HPs eliminates fossil fuel use and tailpipe/on-site greenhouse gas emissions ('emissions'), but causes emissions from electricity generation. Emission intensities in the power sector widely differ across the globe and will change over time 3 . Additionally, producing and recycling EVs and HPs involves higher emissions than producing petrol cars and fossil boilers, due to battery production for EVs, and refrigerant liquid use for HPs 9,10 . The question thus arises as to where and when the electrification of energy end-use could, under a failure to decarbonise electricity generation, increase overall emissions 11,12 .Multi-sectoral mitigation scenarios (such as those reviewed by the IPCC) have identified electrification as a robust policy strategy, but typically focus on a context of rapid power sector decarbonisation 3,13 . However, sector-specific policies and self-reinforcing social and industrial dynamics could as well lead to real-world trajectories in which end-use electrification and power sector decarbonisation take place at completely different rates 14 . In such a c...

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Climate change poses a significant threat to global biodiversity, but freshwater fishes have been largely ignored in climate change assessments. Here, we assess threats of future flow and water temperature extremes to ~11,500 riverine fish species. In a 3.2 °C warmer world (no further emission cuts after current governments’ pledges for 2030), 36% of the species have over half of their present-day geographic range exposed to climatic extremes beyond current levels. Threats are largest in tropical and sub-arid regions and increases in maximum water temperature are more threatening than changes in flow extremes. In comparison, 9% of the species are projected to have more than half of their present-day geographic range threatened in a 2 °C warmer world, which further reduces to 4% of the species if warming is limited to 1.5 °C. Our results highlight the need to intensify (inter)national commitments to limit global warming if freshwater biodiversity is to be safeguarded.

Island faunas can be characterized by gigantism in small animals and dwarfism in large animals, but the extent to which this so-called 'island rule' provides a general explanation for evolutionary trajectories on islands remains contentious. Here we use a phylogenetic metaanalysis to assess patterns and drivers of body size evolution across a global sample of paired island-mainland populations of terrestrial vertebrates. We show that 'island rule' effects are widespread in mammals, birds and reptiles, but less evident in amphibians, which mostly tend towards gigantism. We also found that the magnitude of insular dwarfism and gigantism is mediated by climate as well as island size and isolation, with more pronounced effects in smaller, more remote islands for mammals and reptiles. We conclude that the island rule is pervasive across vertebrates, but that the implications for body size evolution are nuanced and depend on an array of context-dependent ecological pressures and environmental conditions..