Lorenzo

Rosa

By synthetically producing nitrogen fertilizers from ammonia (NH3), the Haber-Bosch process has been feeding humanity for more than one hundred years. However, current NH3 production relies on fossil fuels, and is energy and carbon intensive. This commits humanity to emissions levels not compatible with climate goals and commits agricultural production to fossil fuels dependency. Here, we quantify food and energy implications of transitioning nitrogen fertilizers to net-zero CO2 emissions. We find that 1.07 billion people are fed from food produced from imported nitrogen fertilizers. An additional 710 million people are fed from imported natural gas feedstocks used for fertilizers production, meaning that 1.78 billion people per year are fed from imports of either fertilizers or natural gas. These findings highlight the reliance of global food production on trading and fossil fuels, hence its vulnerability to supply and energy shocks. However, alternative routes to achieve net-zero emissions in NH3 production exist, which are based on carbon capture and storage, electrification, and biomass. These routes comply with climate targets while mitigating the risks associated with food security. Yet, they require more land, energy, and water than business-as-usual production, exacerbating land and water scarcity and the use of limited natural resources. Transitioning fertilizers to net-zero emissions can contribute to climate and food security goals, although water, land, and energy trade-offs should be considered.

Sustainable irrigation expansion over water limited croplands is an important measure to enhance agricultural yields and increase the resilience of crop production to global warming. While existing global assessments of irrigation expansion mainly illustrate the biophysical potential for irrigation, socioeconomic factors such as weak governance or low income, that demonstrably impede the successful implementation of sustainable irrigation, remain largely underexplored. Here we provide five scenarios of sustainable irrigation deployment in the 21st century integrated into the framework of Shared Socioeconomic Pathways, which account for biophysical irrigation limits and socioeconomic constraints. We find that the potential for sustainable irrigation expansion implied by biophysical limits alone is considerably reduced when socioeconomic factors are considered. Even under an optimistic scenario of socio-economic development, we find that additional calories produced via sustainable irrigation by 2100 might reach only half of the maximum biophysical potential. Regions with currently modest socioeconomic development such as Sub-Saharan Africa are found to have the highest potential for improvements. In a scenario of sustainable development, Sub-Saharan Africa would be able to almost double irrigated food production and feed an additional 70 million people compared to 2020, whereas in a scenario where regional rivalry prevails, this potential would be halved. Increasing sustainable irrigation will be key for countries to meet the projected food demands, tackle malnutrition and rural poverty in the context of increasing impacts of anthropogenic climate change on food systems. Our results suggest that improving governance levels for example through enhancing the effectiveness of institutions will constitute an important leverage to increase adaptive capacity in the agricultural sector.

Bioenergy with carbon capture and storage (BECCS) is a carbon dioxide removal (CDR) solution necessary to achieve net-zero-carbon-emissions goals. While the BECCS potential from large industrial emitters has been quantified, the BECCS potential of small emitters, such as biogas facilities, has not been investigated. Moreover, most BECCS solutions rely on the expected availability of large geological storage capacity for future CDR implementation, although the deployment of CO2 transport and storage supply chains is still a barrier for geological carbon storage ambitions. An alternative opportunity for permanent sequestration of CO2 is concrete, in which captured CO2 can be permanently fixed through carbon dioxide mineralization technologies. We describe and discuss this solution by quantifying the potential of a European bioenergy with carbon capture, utilization, and storage (BECCUS) supply chain, which relies on biogenic CO2 from biogas facilities as a CO2 source, and on carbon dioxide mineralization in concrete as a permanent CO2 sink. This solution is available today, can be adopted seamlessly, and does not need economies of scale for its deployment. We find that European biogas facilities produce 24 Mtons of biogenic CO2 per year, of which 4 Mtons of CO2 per year are emitted from facilities already upgrading biogas into bio-methane. We estimate that carbon dioxide mineralization in recycled concrete aggregates in Europe could permanently store up to 8 Mtons of CO2 per year. Despite the limited storage potential, BECCUS supply chains would reduce CO2 transportation distance and system complexity compared to BECCS supply chains, and would result in a marketable product, namely concrete. Overall, carbon dioxide mineralization in recycled concrete aggregates combines carbon utilization with permanent sequestration, hence contributing to carbon-neutrality goals.

Irrigated agriculture accounts for similar to 90% of anthropogenic freshwater consumption, is deployed on 22% of cultivated land, and provides 40% of global food production. Expanding irrigation onto currently underperforming rainfed croplands is crucial to meet future global food demand without further agricultural expansion and associated encroachment of natural ecosystems. Establishing irrigation is also a potential climate adaptation solution to alleviate heat- and water-stress to crops and reduce climate variability and extremes. Despite irrigation being one of the land management practices with the largest environmental and hydroclimatic impacts, the role of irrigation to adapt agriculture to climate change and achieve global sustainability goals has just started to be quantified. This study reviews biophysical opportunities and feedbacks of 'sustainable irrigation'. I describe the concept of sustainable irrigation expansion-where there are opportunities to increase agricultural productivity over currently water-limited rainfed croplands by adopting irrigation practices that do not deplete freshwater stocks and impair aquatic ecosystems. Expanding sustainable irrigation may avert agricultural expansion but create additional externalities that are often neglected. This review highlights major gaps in the analysis and understanding on the role of sustainable irrigation expansion to adapt agriculture to climate change. This study reviews the implications of a potential sustainable irrigation expansion on (a) global food security, (b) hydroclimatic conditions, (c) water quality, (d) soil salinization, (e) water storage infrastructure, and (f) energy use. These implications help to explain the challenges of achieving sustainability in irrigated agriculture and thus also point toward solutions and future research needs.

Providing affordable and nutritious food to a growing and increasingly affluent global population requires multifaceted approaches to target supply and demand aspects. On the supply side, expanding irrigation is key to increase future food production, yet associated needs for storing water and implications of providing that water storage, remain unknown. Here, we quantify biophysical potentials for storage-fed sustainable irrigation-irrigation that neither depletes freshwater resources nor expands croplands but requires water to be stored before use-and study implications for food security and infrastructure. We find that water storage is crucial for future food systems because 460 km3/yr of sustainable blue water, enough to grow food for 1.15 billion people, can only be used for irrigation after storage. Even if all identified future dams were to contribute water to irrigation, water stored in dammed reservoirs could only supply 209 ± 50 km3/yr to irrigation and grow food for 631 ± 145 million people. In the face of this gap and the major socioecologic externalities from future dams, our results highlight limits of gray infrastructure for future irrigation and urge to increase irrigation efficiency, change to less water-intensive cropping systems, and deploy alternative storage solutions at scale.