Abstract: International food trade reshapes regional water scarcity through virtual water transfers (VWT), influencing water use equality and equity. This study examines eight populous yet impoverished countries in Africa and Asia, representing 30 % of the global poor population and contributing 20 % to agricultural VWT. Despite their significant role, these countries have been understudied due to a lack of data or attention. By integrating multiple datasets and models, we assess how international food trade impacts water scarcity, inequality, and inequity within these countries and identify the driving factors. Our findings reveal varied outcomes: Uganda and Ethiopia benefit from reduced water scarcity (∼40 % and ∼7 %) and improved equality and equity (∼90 % and ∼68 %), while India and Pakistan face exacerbated scarcity (∼4 % and ∼2 %) and widening inequality and inequity (∼4 % and ∼7 %). The effects are largely driven by critical trade flows of staple and cash crops like rice, sugar cane, and cotton among developing countries, propelled by comparative advantages in agricultural production, econo-geography, food demand, and water endowment between importers and exporters. Addressing these water challenges involves diversifying import channels to reduce reliance on detrimental trade flows, such as India's rice exports to Iran, while promoting beneficial flows, like Bangladesh's cotton imports from India, through trade agreements. Additionally, implementing pro-poor water policies (e.g., providing water subsidies) and water-saving techniques (e.g., adopting drip irrigation) is crucial, though caution is needed to avoid unintendedly marginalizing vulnerable groups through large-scale water projects.

Abstract: China's pursuit of carbon neutrality target hinges on a profound shift towards low-carbon energy, primarily reliant on intermittent and variable yet crucial solar and wind power sources. In particular, low-solar-low-wind (LSLW) compound extremes present a critical yet largely ignored threat to the reliability of renewable electricity generation. While existing studies have largely evaluated the impacts of average climate-induced changes in renewable energy resources, comprehensive analyses of the compound extremes and, particularly, the underpinning dynamic mechanisms remain scarce. Here we show the dynamic evolution of compound LSLW extremes and their underlying mechanisms across China via coupling multi-model simulations with diagnostic analysis. Our results unveil a strong topographic dependence in the frequency of compound LSLW extremes, with a national average frequency of 16.4 (10th-90th percentile interval ranges from 5.3 to 32.6) days/yr, when renewable energy resource in eastern China are particularly compromised (∼80% lower than that under average climate). We reveal a striking increase in LSLW extremes frequency, ranging from 12.4% under SSP126 to 60.2% under SSP370, primarily driven by both renewable energy resource declines and increasingly heavy-tailed distributions, resulting from weakened meridional temperature (pressure) gradient, increased frequency of extremely dense cloud cover, and additional distinctive influence of increased aerosols under SSP370. Our study underscores the urgency of preparing for significantly heightened occurrences of LSLW events in a warmer future, emphasizing such climate-induced compound LSLW extreme changes are not simply by chance, but rather projectable, thereby underscoring the need for proactive adaptation strategies. Such insights are crucial for countries globally navigating a similar transition towards renewable energy.

Abstract: Climate-driven impacts on future urban heating and cooling (H&C) energy demand are critical to sustainable energy planning. Existing global H&C projections are predominantly made without accounting for future two-way biophysical feedbacks between urban climate and H&C use. Here, using a hybrid modelling framework we show that the prevalent degree-days methods misrepresent the magnitude, nonlinearity and uncertainty in the climate-driven projections of H&C energy demand changes due to the missing two-way feedbacks. We find a 220% increase (47% decrease) in cooling (heating) energy demand with amplified uncertainty by 2099 under a very high emission scenario, roughly twice that projected by previous methods. The spatially diverse H&C demand responses to the warming climates highlight the disparate challenges faced by individual cities and necessitate urban energy planning accounting for local climate–energy interactions. Our study underscores the critical necessity of explicit and dynamic modelling of urban H&C energy use for climate-sensitive energy planning.

Abstract: China pledged to achieve carbon neutrality by 2060 to combat global climate change, yet the resulting multi-aspect domestic impacts are not fully analysed due to an incomplete understanding of the underlying anthropogenic–natural interactions. Building an integrated cross-disciplinary modelling framework that can capture the feedbacks of changing aerosols on meteorology, here we highlight the amplified air quality, human health and renewable energy self-reinforcing synergies of China’s carbon neutral target in comparison to the baseline in 2015 and 2060. We find that owing to emissions reduction and more favourable meteorological conditions caused by less aerosol, achieving China’s carbon neutrality target in 2060 reduces national population-weighted PM2.5 concentrations and associated premature deaths by ~39 μg m−3 and 1.13 (95% confidence interval: 0.97–1.29) million while boosting provincial solar (wind) power performance by up to ~10% (~6%) with mostly decreased resource variability in comparison to the 2060 baseline. Enhanced renewable performance along with low-carbon energy transition may provide additional opportunities to address the remaining air pollution and associated human health damages upon achieving carbon neutrality. Our results highlight that global developing and polluting countries’ pledge for carbon neutrality can produce important positive feedbacks between aerosols mitigation, air quality improvement and enhanced renewable energy, which can be amplified via weakened aerosol–meteorology interactions and better atmospheric dispersion.

Abstract: Freshwater is closely interconnected with multiple sustainable development goals (SDGs). Virtual water transfer associated with agricultural trade may help to mitigate water scarcity (SDG6). However, the resulting impacts on water scarcity distribution among income groups (SDG1) and subsequent effects on water use inequality and inequity (SDG10) remain largely unclear. Here we develop an integrated framework to reveal the asymmetric impacts of international agricultural trade on water use scarcity, inequality and inequity between and within developing and developed countries. We find that although agricultural trade generally relieves water scarcity globally, it disproportionately benefits the rich and widens both the water scarcity and inequity gap between the poor and the rich. Notably, in developing countries, the population (35%) suffering from both increased water scarcity and inequity are the poorest group (per capita income is 16% lower than average), whereas the relatively poor (13% population) in developed countries often simultaneously benefit from decreased water scarcity and reduced inequity synergies. Our results thereby highlight striking asymmetric and generally more favourable trade-induced water impacts for developed countries, urging future water and trade policies striving for a better balance across multiple critical SDGs and achieving sustainable development for all.

Abstract: Water scarcity and climate change are dual challenges that could potentially threaten energy security. Yet, integrated water–carbon management frameworks coupling diverse water- and carbon-mitigation technologies at high spatial heterogeneity are largely underdeveloped. Here we build a global unit-level framework to investigate the CO2 emission and energy penalty due to the deployment of dry cooling—a critical water mitigation strategy—together with alternative water sourcing and carbon capture and storage under climate scenarios. We find that CO2 emission and energy penalty for dry cooling units are location and climate specific (for example, 1–15% of power output), often demonstrating notably faster efficiency losses than rising temperature, especially under the high climate change scenario. Despite energy and CO2 penalties associated with alternative water treatment and carbon capture and storage utilization, increasing wastewater and brine water accessibility provide potential alternatives to dry cooling for water scarcity alleviation, whereas CO2 storage can help to mitigate dry cooling-associated CO2 emission tradeoffs when alternative water supply is insufficient. By demonstrating an integrative planning framework, our study highlights the importance of integrated power sector planning under interconnected dual water–carbon challenges. 

Abstract: Climate change is altering the timing and magnitude of snowmelt, which may either directly or indirectly via global trade affect agriculture and livelihoods dependent on snowmelt. Here, we integrate subannual irrigation and snowmelt dynamics and a model of international trade to assess the global redistribution of snowmelt dependencies and risks under climate change. We estimate that 16% of snowmelt used for irrigation is for agricultural products traded globally, of which over 70% is from five countries. Globally, we observe a prodigious snowmelt dependence and risk diffusion, with particularly evident importing of products at risk in western Europe. In Germany and the UK, local fraction of surface-water-irrigated agriculture supply exposed to snowmelt risks could increase from negligible to 16% and 10%, respectively, under a 2 °C warming. Our results reveal the trade-exposure of agricultural supplies, highlighting regions and crops whose consumption may be vulnerable to changing snowmelt even if their domestic production is not. 

Abstract: Worldwide efforts to switch away from coal have increased the reliance on natural gas imports for countries with inadequate domestic production. In preparing for potential gas import disruptions, there have been limited attempts to quantify the environmental and human health impacts of different options and incorporate them into decision-making. Here, we analyze the air pollution, human health, carbon emissions, and water consumption impacts under a set of planning strategies to prepare for potentially fully disrupted natural gas imports in China. We find that, with China’s current natural gas storage capacity, compensating for natural gas import disruptions using domestic fossil fuels (with the current average combustion technology) could lead up to 23,300 (95% CI: 22,100–24,500) excess premature deaths from air pollution, along with increased carbon emissions and aggravated water stress. Improving energy efficiency, more progressive electrification and decarbonization, cleaner fossil combustion, and expanding natural gas storage capacity can significantly reduce the number of excess premature deaths and may offer opportunities to reduce negative carbon and water impacts simultaneously. Our results highlight the importance for China to increase the domestic storage capacity in the short term, and more importantly, to promote a clean energy transition to avoid potentially substantial environmental consequences under intensifying geopolitical uncertainties in China. Therefore, mitigating potential negative environmental impacts related to insecure natural gas supply provides additional incentives for China to facilitate a clean and efficient energy system transition. 

Abstract: Snowpack stores cold-season precipitation to meet warm-season water demand. Climate change threatens to disturb this balance by altering the fraction of precipitation falling as snow and the timing of snowmelt, which may have profound effects on food production in basins where irrigated agriculture relies heavily on snowmelt runoff. Here, we analyse global patterns of snowmelt and agricultural water uses to identify regions and crops that are most dependent on snowmelt water resources. We find hotspots primarily in high-mountain Asia (the Tibetan Plateau), Central Asia, western Russia, western US and the southern Andes. Using projections of sub-annual runoff under warming scenarios, we identify the basins most at risk from changing snowmelt patterns, where up to 40% of irrigation demand must be met by new alternative water supplies under a 4 °C warming scenario. Our results highlight basins and crops where adaptation of water management and agricultural systems may be especially critical in a changing climate. 

Abstract: Water stress is often evaluated by scarcity: the share of available water supply being consumed by humans. However, some consumptive uses of water are more or less flexible than others, depending on the costs or effects associated with their curtailment. Here, we estimate the share of global water consumption over the period 1980–2016 from the relatively inflexible demands of irrigating perennial crops, cooling thermal power plants, storing water in reservoirs and supplying basic water for humans and livestock. We then construct a water stress index that integrates the share of runoff being consumed (scarcity), the share of consumption in these inflexible categories (flexibility) and the historical variability of runoff weighted by storage capacity (variability), and use our index to evaluate the trends in water stress of global major river basins on six continents. We find that the 10% most stressed basins encompass ~19%, 19% and 35% of global population, thermal electricity generation and irrigated calorie production, respectively, and some of these basins also experience the largest increases in our identified stress indexes over the study period. Water consumption intensities (water used per unit of goods or service produced) vary by orders of magnitude across and within continents, with highly stressed basins in some cases characterized by high water consumption intensities. Our results thus point to targeted water mitigation opportunities (for example, relocating crops and switching cooling technologies) for highly stressed basins. 

Abstract: Both energy production and consumption can simultaneously affect regional air quality, local water stress and the global climate. Identifying the air quality–carbon–water interactions due to both energy sources and end-uses is important for capturing potential co-benefits while avoiding unintended consequences when designing sustainable energy transition pathways. Here, we examine the air quality–carbon–water interdependencies of China’s six major natural gas sources and three end-use gas-for-coal substitution strategies in 2020. We find that replacing coal with gas sources other than coal-based synthetic natural gas (SNG) generally offers national air quality–carbon–water co-benefits. However, SNG achieves air quality benefits while increasing carbon emissions and water demand, particularly in regions that already suffer from high per capita carbon emissions and severe water scarcity. Depending on end-uses, non-SNG gas-for-coal substitution results in enormous variations in air quality, carbon and water improvements, with notable air quality–carbon synergies but air quality–water trade-offs. This indicates that more attention is needed to determine in which end-uses natural gas should be deployed to achieve the desired environmental improvements. Assessing air quality–carbon–water impacts across local, regional and global administrative levels is crucial for designing and balancing the co-benefits of sustainable energy development and deployment policies at all scales. 

Abstract: Facing severe air pollution and growing dependence on natural gas imports, the Chinese government plans to increase coal-based synthetic natural gas (SNG) production. Although displacement of coal with SNG benefits air quality, it increases CO2 emissions. Due to variations in air pollutant and CO2 emission factors and energy efficiencies across sectors, coal replacement with SNG results in varying degrees of air quality benefits and climate penalties. We estimate air quality, human health, and climate impacts of SNG substitution strategies in 2020. Using all production of SNG in the residential sector results in an annual decrease of ∼32,000 (20,000 to 41,000) outdoor-air-pollutionassociated premature deaths, with ranges determined by the low and high estimates of the health risks. If changes in indoor/household air pollution were also included, the decrease would be far larger. SNG deployment in the residential sector results in nearly 10 and 60 times greater reduction in premature mortality than if it is deployed in the industrial or power sectors, respectively. Due to inefficiencies in current household coal use, utilization of SNG in the residential sector results in only 20 to 30% of the carbon penalty compared with using it in the industrial or power sectors. Even if carbon capture and storage is used in SNG production with today’s technology, SNG emits 22 to 40% more CO2 than the same amount of conventional gas. Among the SNG deployment strategies we evaluate, allocating currently planned SNG to households provides the largest air quality and health benefits with the smallest carbon penalties.