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Energy production in the United States for domestic use and export is predicted to rise 27% by 2040. We quantify projected energy sprawl (new land required for energy production) in the United States through 2040. Over 200,000 km2 of additional land area will be directly impacted by energy development. When spacing requirements are included, over 800,000 km2 of additional land area will be affected by energy development, an area greater than the size of Texas. This pace of development in the United States is more than double the historic rate of urban and residential development, which has been the greatest driver of conversion in the United States since 1970, and is higher than projections for future land use change from residential development or agriculture. New technology now places 1.3 million km2 that had not previously experienced oil and gas development at risk of development for unconventional oil and gas. Renewable energy production can be sustained indefinitely on the same land base, while extractive energy must continually drill and mine new areas to sustain production. We calculated the number of years required for fossil energy production to expand to cover the same area as renewables, if both were to produce the same amount of energy each year. The land required for coal production would grow to equal or exceed that of wind, solar and geothermal energy within 2-31 years. In contrast, it would take hundreds of years for oil production to have the same energy sprawl as biofuels. Meeting energy demands while conserving nature will require increased energy conservation, in addition to distributed renewable energy and appropriate siting and mitigation.

Urban tree cover provides benefits to human health and well-being, but previous studies suggest that tree cover is often inequitably distributed. Here, we use National Agriculture Imagery Program digital ortho photographs to survey the tree cover inequality for Census blocks in US large urbanized areas, home to 167 million people across 5,723 municipalities and other Census-designated places. We compared tree cover to summer land surface temperature, as measured using Landsat imagery. In 92% of the urbanized areas surveyed, low-income blocks have less tree cover than high-income blocks. On average, low-income blocks have 15.2% less tree cover and are 1.5⁰C hotter than high-income blocks. The greatest difference between low- and high-income blocks was found in urbanized areas in the Northeast of the United States, where low-income blocks in some urbanized areas have 30% less tree cover and are 4.0⁰C hotter. Even after controlling for population density and built-up intensity, the positive association between income and tree cover is significant, as is the positive association between proportion non-Hispanic white and tree cover. We estimate, after controlling for population density, that low-income blocks have 62 million fewer trees than high-income blocks, equal to a compensatory value of$56 billion ($ 1,349/person). An investment in tree planting and natural regeneration of $17.6 billion would be needed to close the tree cover disparity, benefitting 42 million people in low-income blocks.

Nearly 3 billion additional urban dwellers are forecasted by 2050, an unprecedented wave of urban growth. While cities struggle to provide water to these new residents, they will also face equally unprecedented hydrologic changes due to global climate change. Here we use a detailed hydrologic model, demographic projections, and climate change scenarios to estimate per-capita water availability for major cities in the developing world, where urban growth is the fastest. We estimate the amount of water physically available near cities and do not account for problems with adequate water delivery or quality. Modeled results show that currently 150 million people live in cities with perennial water shortage, defined as having less than 100 L per person per day of sustainable surface and groundwater flow within their urban extent. By 2050, demographic growth will increase this figure to almost 1 billion people. Climate change will cause water shortage for an additional 100 million urbanites. Freshwater ecosystems in river basins with large populations of urbanites with insufficient water will likely experience flows insufficient to maintain ecological process. Freshwater fish populations will likely be impacted, an issue of special importance in regions such as India's Western Ghats, where there is both rapid urbanization and high levels of fish endemism. Cities in certain regions will struggle to find enough water for the needs of their residents and will need significant investment if they are to secure adequate water supplies and safeguard functioning freshwater ecosystems for future generations.

Concern over climate change has led the U.S. to consider a cap-and-trade system to regulate emissions. Here we illustrate the land-use impact to U.S. habitat types of new energy development resulting from different U.S. energy policies. We estimated the total new land area needed by 2030 to produce energy, under current law and under various cap-and-trade policies, and then partitioned the area impacted among habitat types with geospatial data on the feasibility of production. The land-use intensity of different energy production techniques varies over three orders of magnitude, from 1.9-2.8 km(2)/TW hr/yr for nuclear power to 788-1000 km(2)/TW hr/yr for biodiesel from soy. In all scenarios, temperate deciduous forests and temperate grasslands will be most impacted by future energy development, although the magnitude of impact by wind, biomass, and coal to different habitat types is policy-specific. Regardless of the existence or structure of a cap-and-trade bill, at least 206,000 km(2) will be impacted without substantial increases in energy efficiency, which saves at least 7.6 km(2) per TW hr of electricity conserved annually and 27.5 km(2) per TW hr of liquid fuels conserved annually. Climate policy that reduces carbon dioxide emissions may increase the areal impact of energy, although the magnitude of this potential side effect may be substantially mitigated by increases in energy efficiency. The possibility of widespread energy sprawl increases the need for energy conservation, appropriate siting, sustainable production practices, and compensatory mitigation offsets.

The year 2007 was the first year in which more than half of humanity lived in cities. Over the next 25 years, the world will see the addition of nearly one million km² of urban area, occurring in tens of thousands of cities around the globe. The form these new neighborhoods take will affect our planet's ecology profoundly. Here, I highlight the connection between urban form and ecosystem service generation and consumption. I also discuss how urban form controls energy use, and hence oil security and climate change. I argue that only by directly addressing the implications of urban growth as a research subject will ecologists meet their responsibility to provide a foundation for a sustainable biosphere, a mandate of the Ecological Society of America.

Agricultural irrigation practices will likely be affected by climate change. In this paper, we use a statistical model relating observed water use by U.S. producers to the moisture deficit, and then use this statistical model to project climate changes impact on both the fraction of agricultural land irrigated and the irrigation rate (m³ ha⁻¹). Data on water withdrawals for US states (1985-2005) show that both quantities are highly positively correlated with moisture deficit (precipitation--PET). If current trends hold, climate change would increase agricultural demand for irrigation in 2090 by 4.5-21.9 million ha (B1 scenario demand: 4.5-8.7 million ha, A2 scenario demand: 9.1-21.9 million ha). Much of this new irrigated area would occur in states that currently have a wet climate and a small fraction of their agricultural land currently irrigated, posing a challenge to policymakers in states with less experience with strict regulation of agriculture water use. Moreover, most of this expansion will occur in states where current agricultural production has relatively low market value per hectare, which may make installation of irrigation uneconomical without significant changes in crops or practices by producers. Without significant increases in irrigation efficiency, climate change would also increase the average irrigation rate from 7,963 to 8,400-10,415 m³ ha⁻¹ (B1 rate: 8,400-9,145 m³ ha⁻¹, A2 rate: 9,380-10,415 m³ ha⁻¹). The irrigation rate will increase the most in states that already have dry climates and large irrigation rates, posing a challenge for water supply systems in these states. Accounting for both the increase in irrigated area and irrigation rate, total withdrawals might increase by 47.7-283.4 billion m³ (B1 withdrawal: 47.7-106.0 billion m³, A2 withdrawal: 117.4-283.4 billion m³). Increases in irrigation water-use efficiency, particularly by reducing the prevalence of surface irrigation, could eliminate the increase in total irrigation withdrawals in many states.

Coastal ecosystems have the potential to contribute to disaster risk reduction and adaptation to climate change. While previous studies have estimated the value of current coastal ecosystems for reducing coastal risk, there have been relatively few studies that look at changes in ecosystem service provision, in the past and under climate change. We employ the probabilistic, event-based CLImate ADAptation platform (CLIMADA) to quantify the protection from tropical cyclones (TCs) provided by coastal ecosystems, modeling the number of beneficiaries in the past and under future climate change. We also investigate the potential of nature-based solutions (NbS), such as mangrove restoration. We find that currently, one in five (21%) of all people impacted annually by TCs in the global low-elevation coastal zone is within the protection distance of coastal ecosystems. Over the last 30 years, the share of protected people has decreased by approximately 2%, due to ecosystem loss. With climate change, the average annual number of people impacted will increase by 40%. Simultaneously, the proportion of people protected by coastal ecosystems with climate change decreases due to changes in TC distribution (−1%). The importance of current coastal protection, and the potential for increasing protection by NbS, varies widely between countries. While the number of people protected globally only increases slightly with mangrove restoration, the share of people protected in individual countries can increase by up to 39%. Our findings provide a basis for NbS planning and adaptation policy, by highlighting areas which will be crucial for coastal protection services in a world altered by climate change.

Green spaces in urban areas—like remnant habitat, parks, constructed wetlands, and street trees—supply multiple benefits. Many studies show green spaces in and near urban areas play important roles harbouring biodiversity and promoting human well‐being. On the other hand, evidence suggests that greater human population density enables compact, low‐carbon cities that spare habitat conversion at the fringes of expanding urban areas, while also allowing more walkable and livable cities. How then can urban areas have abundant green spaces as well as density? In this paper, we review the empirical evidence for the relationships between urban density, nature, and sustainability. We also present a quantitative analysis of data on urban tree canopy cover and open space for United States large urbanized areas, as well as an analysis of non‐US Functional Urban Areas in OECD countries. We found that there is a negative correlation between population density and these green spaces. For Functional Urban Areas in the OECD, a 10% increase in density is associated with a 2.9% decline in tree cover. We argue that there are competing trade‐offs between the benefits of density for sustainability and the benefits of nature for human well‐being. Planners must decide an appropriate density by choosing where to be on this trade‐off curve, taking into account city‐specific urban planning goals and context. However, while the negative correlation between population density and tree cover is modest at the level of US urbanized areas (R2 = 0.22), it is weak at the US Census block level (R2 = 0.05), showing that there are significant brightspots, neighbourhoods that manage to have more tree canopy than would be expected based upon their level of density. We then describe techniques for how urban planners and designers can create more brightspots, identifying a typology of urban forms and listing green interventions appropriate for each form. We also analyse policies that enable these green interventions illustrating them with the case studies of Curitiba and Singapore. We conclude that while there are tensions between density and urban green spaces, an urban world that is both green and dense is possible, if society chooses to take advantage of the available green interventions and create it. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog.

Investments in watershed services (IWS) programs, in which downstream water users pay upstream watershed service suppliers for actions that protect drinking water, are increasing in number and scope. IWS programs represent over $170 million of investment in over 4.3 million ha of watersheds, providing water to over 230 million people. It is not yet fully clear what factors contribute to the establishment and sustainability of IWS. We conducted a representative global analysis of 416 of the world’s largest cities, including 59 (14%) with IWS programs. Using random forest ensemble learning methods, we evaluated the relative importance of social and ecological factors as predictors of IWS presence. IWS programs are more likely present in source watersheds with more agricultural land and less protected area than otherwise similar watersheds. Our results suggest potential to expand IWS as a strategy for drinking water protection and also contribute to decisions regarding suitable program locations. Investment in watershed services programs is growing, however the factors that contribute to sustainability of such programs are unclear. Here the authors use a large database of cities around the world to show that payment schemes are more likely to be present in watersheds with more agricultural land and less protected areas.

As the global urban population is poised to grow by 2.5 billion over the next 30 y, urban land conversions are expected to be an increasingly prominent driver of habitat and biodiversity loss. Mitigating these impacts urgently requires an improved understanding of where and how these biodiversity losses might occur. Here, we use a recently developed suite of land-use projections to provide an assessment of projected habitat that will be lost to urban land expansion for 30,393 species of terrestrial vertebrates from 2015 to 2050 across three shared socioeconomic pathway (SSP) scenarios. We find that urban land expansion is a contributing driver of habitat loss (≥5% of total loss) for around one-third (26 to 39%) of the species assessed. For up to 855 species (2 to 3% of those assessed), urban land is a direct driver of species imperilment, driving at least one-quarter of a net habitat loss of 10% or more. Urban clusters with the greatest threats to species due to projected expansion are predominantly located in the developing tropical regions of sub-Saharan Africa, South America, Mesoamerica, and Southeast Asia. Our results suggest that strategies for minimizing the impacts of urban land could strengthen global biodiversity protection agreements. Collaborative, global action that focuses on vulnerable species and regions may represent an efficient strategy for avoiding the impacts forecast by our analysis.