Recent global increases in food demand have been largely driven by demographic growth and improvements in income . Since World War II, population has more than tripled from 2.4 billion to 7.3 billion people ; South and East Asia experienced the most substantial increases . Rising incomes have allowed households to afford richer diets with higher calorie and protein intake per capita but often with stronger burdens on natural resources and the environment . A typical trend observed in countries undergoing economic development is that, as the average income increases, there is a growth in the consumption of non-starchy food such as vegetables, dairy,meat, and consumable oil , a pattern that is also known as “Bennett’s law” . Indeed, per capita consumption of animal food has been increasing in the last few decades . Dairy and meat production are expected to increase by 65% and 76%, respectively, by 2050 . Such an increase in the consumption of animal products can impede humanity’s ability to meet greenhouse gas emission targets . The general improvement in household economic status has meant that 123 million people in developing countries were able to escape undernourishment between 1990 and 2015 alone . Yet substantial nutrition deficiencies persist with roughly one in seven people receiving inadequate protein and calories and still more lacking access to important micro-nutrients .Despite massive increases in crop production over the past 50 years,aeroponic tower garden system a growing share of this output is not being used for direct human consumption. The growth in demand for animal products , combined with a shift toward a more crop-dependent livestock sector, has substantially increased competition for crop use between direct human consumption and feed to support livestock.

Indeed, the excess in crop production afforded by the technological advances of the green revolution has allowed for the use of crops as feed, thereby dramatically increasing the rates of livestock production, a phenomenon known as the “livestock revolution” . This new system of livestock production has increasingly relied on concentrated animal feed operations as an alternative to range land production . Owing in large part to the usage of energy-rich oil cakes as feed, 51% of the world’s crop calories are currently devoted to animal production . This trend has meant that countries with emerging economies and a rising middle class have had to depend more heavily on feed imports, mainly from the United States, Brazil, and Argentina, in order to support domestic animal production . Likewise, the global demand for seafood has increased and has been met by increased fish and seafood production in aquaculture operations, while increasing the pressure on wild fisheries . In addition to demographic and dietary drivers, there has been a rapid increase in demand for crop-based bio-fuels since the start of the 21st century , driven in part by clean energy mandates in the United States and the EU Parliament . This has led to the growing diversion of crop supply, mainly maize in the United States, sugarcane in Brazil, rapeseed in Europe, and oil palm in Indonesia and Malaysia, toward the production of bioethanol and bio-diesel . Although in 2000 only about 3% of crop supply was used for bio-fuel production, diversion of human-edible calories to crop-based bio-fuels increased dramatically during 2000–2010 . Rulli et al. estimate that the crops diverted to bio-fuel use could feed nearly 300 million people if they were used as food. In addition, the rise in bio-fuel demand has had an important influence on food commodity markets; several studies provide evidence that bio-fuels have contributed substantially to higher food prices, as well as increased market volatility .

Thus, it is clear that these first-generation bio-fuels have served to further increase competition for crop use and the resources to support food production. Another key component in the fate of global crop production is that of food waste. Roughly one-quarter of food production is lost or wasted at various steps along the food supply chain, from losses during production to uneaten food on a person’s plate, with distinct regional patterns . In Asia and sub-Saharan Africa, the vast majority of food losses occur during the early stages of the supply chain as a result of large production losses from dry spells, flooding, and tropical disease, as well as inadequate storage. In contrast, for Europe and North America, approximately one third of food waste occurs at either the retailer level or the consumer level .The wide diffusion of fertilizers and high-yielding crop varieties has led to much of the tripling in food supply, which to some degree has likely avoided even greater expansion of croplands. However, this intensification of agriculture to prevent the widespread conversion of natural systems has come with important trade-offs , promoting cultivation practices with extensive environmental consequences that were often inadvertently supported by policies and subsidies . For instance, over application of fertilizers, pesticides, and herbicides is a major contributor to non-point source pollution, eutrophication of water bodies, loss of soil biodiversity, GHG emissions, and acid rain . As a result, the global food system has become one of the most extensive ways by which humanity has modified the environment .More than one half of the accessible runoff is withdrawn for human use , and nearly all of the anthropogenic consumptive water use is for agriculture . The mechanization of agricultural production has allowed for intensified soil tillage, thereby increasing the rates of soil loss, which by far exceed those of soil formation .

Fertilizer production has more than doubled the amount of reactive nitrogen in the environment , and GHG emissions from food production and land use change contribute 19–30% of humanity’s GHG emissions . GHG emissions from agricultural activities increased annually by 1.1% from year 2000 to 2010 . The livestock sector contributes disproportionately to the environmental burden of food production . Although animal production makes up 25% of the world’s food supply by weight, 18% of dietary calories, and 39% of protein , it accounts for approximately 75% of agricultural land area , 29–43% of the total agricultural water footprint , 46–74% of agricultural GHG emissions , and 34–58% of total nitrogen use . The overall greater footprint of livestock production is in large part attributable to the inefficiencies by which plant biomass can be incorporated into animal tissue, particularly for cattle . Owing in large part to the efficient feed conversion ratios of monogastric digestion, as well as the inherent variability in range land biomass production , the world’s livestock systems have been transitioning from an extensive, beef-dominated system toward a focus on concentrated, feed-reliant pig and chicken production . This trend has led to important environmental trade-offs that have occurred within the livestock sector, where improvements in land use efficiency and GHG emissions per unit of animal production have been offset by the increasing water and nitrogen requirements of feed production . Animal agriculture is a major source of GHG emissions, land use,dutch bucket for sale and water consumption. Interestingly, pets such as dogs and cats are also major contributors to the demand for animal products. A recent study for the United States has shown that dogs and cats account for roughly 25–30% of the land, water, and phosphate footprint of animal production . A decrease in the reliance on animal-derived products can reduce environmental impacts and increase food security. A recent study, which modeled the U.S. agricultural system without farmed animals, found that, without animal food production, the total food production of the United States would increase by 23% and total agricultural GHG emissions would decrease by 28% . However, in this system modeled without farmed animals, population diet of the United States resulted in the absence of essential nutrients that are present only in animal products .Global food production is facing mounting constraints to its continued growth. These limitations fall into two broad categories related to changing climate and bounds imposed by plant physiology and production decisions. Regarding the first, there is evidence of reductions in food production resulting from climate change in recent decades, though overall production gains have been able to overcome these reductions so far . Early work on this topic showed that between 1981 and 2002 the combined production of three major crops—barley, maize, and wheat—was reduced by 40 Mt/year, compared to a case with no climate effect . From 1980 to 2008, global wheat and maize production fell 4% and 6%, respectively, below what would be expected without climate trends; these effects varied widely across crops and countries . It has been estimated that, without accounting for the effect of CO2 fertilization, each degree Celsius of mean global temperature increase is expected to induce a 6.0% drop in the global yield of wheat, 3.2% of rice, 7.4% of maize, and 3.1% of soybean .

Other work has shown that as much of one third of global crop yield variability can be explained by inter annual fluctuations in temperature or precipitation, with climate variability explaining as much as 60% of yield variability in certain breadbasket areas . Moreover, extreme droughts and heat waves, which are expected to intensify under climate change, can strongly reduce crop production . Recent modeling efforts created an ensemble of models that consider a different configuration of carbon dioxide under most recent climate projections . Regarding livestock, there has been substantial investigation of the effects of heat stress on animal production , but to date, no studies have examined the relation between animal productivity and inter annual climate variability. Even though historical effects of climate trends on food systems have been modest and masked by overall gains in production from specific regions, it is expected that climate change impacts on food production will become more pronounced in the coming decades, depending on the GHG emissions trajectory considered . The second set of constraints to production, which are related to crop physiology and production decisions, play an important role as well. Many places around the world—23–37% of maize, rice, soybean, and wheat areas—are experiencing a plateau or collapse of major crop yields from a combination of biophysical and socioeconomic factors . In areas that continue to realize overall yield gains, there are emerging indications that these improvements are being disproportionately contributed by a small fraction of highly productive cropland, whereas yields in other cultivated areas have increased more slowly. Pointing to this, a recent study focused on maize in the U.S. Midwest showed that the greatest yield improvements are being provided by a narrowing area of cropland . Along with these features of yield trends, the efficient use of fertilizers for cereal production has also plateaued, as the highest returns on nutrient inputs occur when yields are low . The nutritional quality of global cereal production has declined steadily with time, as nutrient-rich cereals have been supplanted by high-yielding rice, wheat, and maize varieties . This increase in high-yielding crop production has been in part driven by the increasing prevalence of large farms, which generally produce a less nutritionally diverse set of crops , and has resulted in dwindling amounts of key nutrients, such as protein, iron, and zinc per tons of cereal crop . Enhancements of atmospheric CO2 concentrations are expected to exacerbate these declines by adversely affecting crop nutrient content in plant tissue, especially in C3 crops . Though food supply remains largely nutritionally adequate at the global scale, the persisting challenges of food access, widespread malnourishment, and nutrient deficiencies amplify these trends of declining nutritional quality. Though not explored in depth here, other important factors also serve to curtail food production. For instance, desertification and soil salinization have rendered large amounts of arable land and grazing areas unusable . Urbanization has removed a fraction of fertile cropland from active production . Excess surface ozone has further led to relative yield decreases of between 3% and 16% for maize, rice, soybeans, and wheat .Human societies rely on freshwater resources for a variety of activities, including drinking, household usage, and industrial and agricultural production . Agricultural uses, however, by far exceed any other form of human appropriation of freshwater resources .