Great progress has been made in addressing global undernutrition over the past several decades, in part because of large increases in food production from agricultural expansion and intensification. Food systems, however, face continued increases in demand and growing environmental pressures. Most prominently, human-caused climate change will influence the quality and quantity of food we produce and our ability to distribute it equitably. Our capacity to ensure food security and nutritional adequacy in the face of rapidly changing biophysical conditions will be a major determinant of the next century's global burden of disease. In this article, we review the main pathways by which climate change may affect our food production systems—agriculture, fisheries, and livestock—as well as the socioeconomic forces that may influence equitable distribution.

How will the 10 billion people expected to be living on Earth by 2050 obtain sufficient and nutritious food? This is one of the greatest challenges humanity faces. Global food systems must supply enough calories and protein for a growing human population and provide important micronutrients such as iron, zinc, omega-3 fatty acids and vitamins. Deficiencies of micronutrients — so called because the body needs them only in tiny amounts — can increase the risks of perinatal and maternal mortality, growth retardation, child mortality, cognitive deficits and reduced immune function1. The associated burdens of disease are large. Forty-five per cent of mortality in children under five is attributable to undernutrition; nutritional deficiencies are responsible for 50% of years lived with disability in children aged four and under1. Fish are crucial sources of micronutrients, often in highly bioavailable forms. And fish populations are declining. Most previous analyses have considered only how people will be affected by the loss of protein derived from fish. We calculate that this is the tip of the iceberg. Combining data on dietary nutrition, and fish catch, we predict that more than 10% of the global population could face micronutrient and fatty-acid deficiencies driven by fish declines over the coming decades, especially in the developing nations at the Equator (see 'Troubled Waters'). This new view underlines the need for nutrition-sensitive fisheries policies. Presently, 17% of the global population is zinc deficient, with some subpopulations being particularly at risk1. Nearly one-fifth of pregnant women worldwide have iron-deficiency anaemia and one-third are vitamin-A deficient1. We estimate that 845 million people (11% of the current global population) are poised to become deficient in one of these three micronutrients if current trajectories in fish-catch declines continue. Considering nutrients found only in foods derived from animals, such as vitamin B12, and DHA omega-3 fatty acids (almost exclusively derived from meat consumption, see Supplementary Information), we calculate that 1.39 billion people worldwide (19% of the global population) are vulnerable to deficiencies because fish make up more than 20% of their intake of these foods by weight. To make this sobering new assessment, we coupled two databases from 2010, the most recent year for which both had data. The new Global Expanded Nutrient Supply (GENuS) database combines food balance sheets (total quantity of food production and imports minus livestock feed, post-harvest losses, and exports) and production or trade data from the Food and Agriculture Organization of the United Nations (FAO) with estimates of food group intake by age and sex2. It estimates per capita edible supplies for 225 foods, paired with regional food composition tables to infer nutrient supplies by country. GENuS is supported by the Bill and Melinda Gates Foundation and the Winslow Foundation. We categorized populations as nutritionally vulnerable if their nutrient supply was less than double the estimated average requirement (EAR), and if they derived from fish more than 10% of their vitamin A or zinc, or more than 5% of their iron. We chose to double the EAR for two reasons. First, even in countries where the national average intake is greater than the EAR, large variability of intake may still mean that a significant part of the population is eating less well. If we had used the EAR as our threshold, more than 50% of a nation's population would need to be deemed at risk of nutritional deficiency, which we feel is an irresponsibly high proportion required for raising an alarm. Second, our GENuS-derived estimates measure food supply rather than food intake, and are generally regarded as overestimates of true intake2. The Sea Around Us database, released in 2016, provides a portrait of marine fisheries catch between 1950 and 2010 for every coastal nation3. Over 15 years, a team of researchers in every coastal country collated information from government documents, academic research and maritime records to reconstruct the numbers of fish caught. This database measures the contribution of subsistence, artisanal and industrial marine fisheries to food supply at the country level more accurately than previous estimates3. This database was funded by the Pew Charitable Trust and the Paul G. Allen Family Foundation and is maintained by staff at the University of British Columbia in Vancouver, Canada. These global marine catch data are alarming. Conservative estimates by the FAO characterize global fisheries as stable, but acknowledge that global catch has declined by 0.38 million tonnes per year since 1996 (ref. 4). The Sea Around Us estimates summarized earlier this year3 paint a much bleaker picture, in which fish catch peaked in 1996 and has been falling by 1.22 million tonnes (roughly 1%) per year since — three times faster than the decline reported by FAO. The degradation of marine habitat by destructive fishing practices, industrial pollution, climate change and coastal development for urbanization and aquaculture is likely to further degrade ocean ecosystems and reduce fisheries yields. Such patterns call into question the ability of wild fisheries to support future demand for fish. The health impacts of fishery declines will hit some places harder than others. A perfect storm is brewing in the low-latitude developing nations. This is where human nutrition is most dependent on wild fish, and where fisheries are most at risk from illegal fishing, weak governance, poor knowledge of stock status, population pressures and climate change. Sharp declines in the health of fisheries were first described in the twentieth century in high-latitude regions where industrial fishing began, such as the northwest Atlantic Ocean. Developed countries have compensated with intensive agricultural production, by importing goods (including fish),...

Understanding dietary patterns is vital to reducing the number of people experiencing hunger (about 795 million), micronutrient deficiencies (2 billion), and overweight or obesity (2.1 billion). We characterize global trends in dietary quality by estimating micronutrient density of the food supply, prevalence of inadequate intake of 14 micronutrients, and average prevalence of inadequate intake of these micronutrients for all countries between 1961 and 2011. Over this 50-year period, the estimated prevalence of inadequate intakes of micronutrients has declined in all regions due to increased total production of food and/or micronutrient density. This decline has been particularly strong in East and Southeast Asia and weaker in South Asia and sub-Saharan Africa. Sub-Saharan Africa is the only region where dietary micronutrient density has declined over this 50-year period. At the global level, micronutrients with the lowest levels of adequate estimated intake are calcium, iron, vitamin A, and zinc, but there are strong differences between countries and regions. Fortification has reduced the estimated prevalence of inadequate micronutrient intakes in all low-income regions, except South Asia. The food supply in many countries is still far below energy requirements, which suggests a need to increase the availability and accessibility of nutritious foods. Countries where the food energy supply is adequate show a very large variation in dietary quality, and in many of these countries people would benefit from more diverse diets with a greater proportion of micronutrient-dense foods. Dietary quality can be improved through fortification, biofortification, and agricultural diversification, as well as efforts to improve access to and use of micronutrient-dense foods and nutritional knowledge. Reducing poverty and increasing education, especially of women, are integral to sustainably addressing malnutrition.

Increasing atmospheric concentrations of carbon dioxide (CO2) affect global nutrition via effects on agricultural productivity and nutrient content of food crops. We combined these effects with economic projections to estimate net changes in nutrient availability between 2010 and 2050. In this modelling study, we used the International Model for Policy Analysis of Agricultural Commodities and Trade to project per capita availability of protein, iron, and zinc in 2050. We used estimated changes in productivity of individual agricultural commodities to model effects on production, trade, prices, and consumption under moderate and high greenhouse gas emission scenarios. Two independent sources of data, which used different methodologies to determine the effect of increased atmospheric CO2 on different key crops, were combined with the modelled food supply results to estimate future nutrient availability. Although technological change, market responses, and the effects of CO2 fertilisation on yield are projected to increase global availability of dietary protein, iron, and zinc, these increases are moderated by negative effects of climate change affecting productivity and carbon penalties on nutrient content. The carbon nutrient penalty results in decreases in the global availability of dietary protein of 4·1%, iron of 2·8%, and zinc of 2·5% as calculated using one dataset, and decreases in global availability of dietary protein of 2·9%, iron of 3·9%, and zinc of 3·4% using the other dataset. The combined effects of projected increases in atmospheric CO2 (ie, carbon nutrient penalty, CO2 fertilisation, and climate effects on productivity) will decrease growth in the global availability of nutrients by 19·5% for protein, 14·4% for iron, and 14·6% for zinc relative to expected technology and market gains by 2050. The many countries that currently have high levels of nutrient deficiency would continue to be disproportionately affected. This approach is an improvement in estimating future global food security by simultaneously projecting climate change effects on crop productivity and changes in nutrient content under increased concentrations of CO2, which accounts for a much larger effect on nutrient availability than CO2 fertilisation. Regardless of the scenario used to project future consumption patterns, the net effect of increasing concentrations of atmospheric CO2 will slow progress in decreasing global nutrient deficiencies. US Environmental Protection Agency, Consultative Group on International Agricultural Research (CIGAR) Research Program on Policies, Institutions and Markets (PIM), and the CGIAR Research Program on Climate Change and Food Security (CCAFS).