Climate change unequally affects nitrogen use and losses in global croplands

Abstract

Maintaining food production while reducing agricultural nitrogen pollution is a grand challenge under the threats of global climate change, which has exerted negative impacts on agricultural sustainability. How global agricultural nitrogen use and loss respond to climate change on temporal and spatial scale is rarely understood. Here we show that climate change leads to small temporal but substantial spatial changes in cropland nitrogen use and losses across global regions based on historical data for the period 1961-2018 from 150 countries. Increases of yield, nitrogen surplus and nitrogen use e ciency (NUE) are identi ed in 24% of countries, while reductions are observed for the remaining 76% of countries, as a result of climate change in 2018. Changes of cropland area per capita of rural population (CAPRP) further intensify the variations of nitrogen use and pollution in global croplands. Yet, improving farmers' practices with changes of CAPRP can facilitate climate change adaptation, by which global cropland NUE could be increased by one-third in 2100 compared to 2018 under future shared socioeconomic pathways. Our results would be of great signi cance to sustain global agriculture as well as eliminate national inequalities on food production and agricultural pollution control. Full TextGlobal climate change has led to an increase in both average ambient temperatures observed and the frequency of extremek weather events, including dry-hot and precipitation extremes 1-3 These changes not only threaten human and ecosystem health, but also adversely affect agricultural production 4, 5 . Mitigating the negative impacts of climate change on agriculture is a grand challenge, in the context of safeguarding food security for a growing and increasingly wealthy global population.Nitrogen (N) fertilizer use has fed about half of the global population 6 ; however, only N use in croplands has exceeded the safe planetary boundary, leading to substantial environmental problems such as air and water pollution, biodiversity loss, soil acidi cation and climate change (ozone layer depletion and nitrous oxide (N 2 O) emission) 7, 8 . Currently, over 100 million tonnes of fertilizer N is applied to global croplands annually and over half of the N is lost to the environment, leading to an average N use e ciency (NUE) below 50%, a critical indicator for agricultural sustainability 8,9 . So far, climate change impacts have been rarely considered when developing management strategies for sustainable agricultural N use, as the focus has been primarily on the climate effects of N fertilizer use, such as N 2 O emissions 10 . Yet, climate change can affect agricultural N use and losses, for instance, and warming temperatures can increase ammonia emissions from croplands 11,12 .The warming climate has been shown to aggravate N pollution in Australia 13 . Eutrophication will become more prevalent during the 21 st century due to precipitation pattern changes 14 .Here, we quanti ed the impact of climate change (annual mean temperature, annu...

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