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Although reactive nitrogen (Nr) emissions from food and energy production contribute to multi-dimensional environmental damages, integrated management of Nr is still lacking owing to unclear future mitigation potentials and benefits. Here, we find that by 2050, high-ambition compared to low-ambition N interventions reduce global ammonia and nitrogen oxide emissions by 21 and 22 TgN/a, respectively, equivalent to 40 and 52% of their 2015 levels. This would mitigate population-weighted PM2.5 by 6 g/m 3 and avoid premature deaths by 817 k (16%), mitigate ozone by 4 ppbv, avoid premature deaths by 252k (34%) and crop yield losses by 122 million tons (4.3%), and decrease terrestrial ecosystem areas exceeding critical load by 420 Mha (69%). Without nitrogen interventions, most environmental damages examined will deteriorate between 2015 and 2050; Africa and Asia are the most vulnerable but also benefit the most from interventions. Nitrogen interventions support sustainable development goals related to air, health, and ecosystems.

Since the 1980s, the widespread use of N fertilizer has not only resulted in a strong increase in agricultural productivity but also caused a number of environmental problems, induced by excess reactive N emissions. A range of approaches to improve N management for increased agricultural production together with reduced environmental impacts has been proposed. The 4R principles (right product, right amount, right time and right place) for N fertilizer application have been essential for improving crop productivity and N use efficiency while reducing N losses. For example, site-specific N management (as part of 4R practice) reduced N fertilizer use by 32% and increased yield by 5% in China. However, it has not been enough to overcome the challenge of producing more food with reduced impact on the environment and health. This paper proposes a new framework of food-chainnitrogen-management (FCNM). This involves good N management including the recycling of organic manures, optimized crop and animal production and improved human diets, with the aim of maximizing resource use efficiency and minimizing environmental emissions. FCNM could meet future challenges for food demand, resource sustainability and environmental safety, key issues for green agricultural transformation in China and other countries. [ABSTRACT FROM AUTHOR]

Highlights • Combined approach to nitrogen and phosphorus pollution can generate co- benefits • Co-benefits key to cost-effectively achieving international environmental goals • Joint abatement measures exist for wastewater, agriculture and consumers • Policy challenges remain: essential resources and different chemical properties • Near-term opportunities: integration of nitrogen and phosphorus management into national climate and sustainable development plans Abstract The United Nations Sustainable Development Goals (SDGs) and the Paris Climate Agreement are possibly the two most important pieces of international environmental policy thus far this century. The SDGs set a number of socioeconomic and environmental targets to be achieved by 2030, and the Paris Climate Agreement provides a framework for the international community to stay below the 2 °C temperature threshold. Such a range of ambitious goals will require measures that can simultaneously address several issues and produce multiple co-benefits, from improved water quality to reduced food waste. A joint approach to reducing nitrogen and phosphorus pollution is a prime example given their myriad impacts on the environment and human health. This study assesses the national climate plans of fifteen countries for language indicating a target or clear commitment that could involve improved N and P management. These countries represent 75% of both global greenhouse gas emissions and N and P consumption. We find that a joint approach could make important contributions to achieving all the national climate plans analyzed and 7 out of 17 SDGs. Joint abatement measures exist for wastewater, agriculture and consumer behavior. Challenges to a joint approach to nitrogen and phosphorus management include their role as essential nutrients and key differences in their availability and chemistry. Whilst there is currently insufficient integration between science, policies and practice on this issue, near-term policy opportunities exist. Looking forward, how humanity manages its relationship with these essential nutrients over the coming decades will be a key bellwether of whether sustainable development is truly achievable. [ABSTRACT FROM AUTHOR]

• Nitrogen pollution is a critical environmental issue. • Scoping the range of possible future nitrogen flows is crucial. • New nitrogen narratives are presented based on the Shared Socioeconomic Pathways. • They can help to understand how to achieve both environment and development goals. Humanity's transformation of the nitrogen cycle has major consequences for ecosystems, climate and human health, making it one of the key environmental issues of our time. Understanding how trends could evolve over the course of the 21st century is crucial for scientists and decision-makers from local to global scales. Scenario analysis is the primary tool for doing so, and has been applied across all major environmental issues, including nitrogen pollution. However, to date most scenario efforts addressing nitrogen flows have either taken a narrow approach, focusing on a singular impact or sector, or have not been integrated within a broader scenario framework – a missed opportunity given the multiple environmental and socio-economic impacts that nitrogen pollution exacerbates. Capitalizing on our expanding knowledge of nitrogen flows, this study introduces a framework for new nitrogen-focused narratives based on the widely used Shared Socioeconomic Pathways that include all the major nitrogen-polluting sectors (agriculture, industry, transport and wastewater). These new narratives are the first to integrate the influence of climate and other environmental pollution control policies, while also incorporating explicit nitrogen-control measures. The next step is for them to be used as model inputs to evaluate the impact of different nitrogen production, consumption and loss trajectories, and thus advance understanding of how to address environmental impacts while simultaneously meeting key development goals. This effort is an important step in assessing how humanity can return to the planetary boundary of this essential element over the coming century. [ABSTRACT FROM AUTHOR]