Feeding 10 Billion

By Stephen Porder and Radika Bhaskar

Developed by the Laboratory for Educational Innovation at the Sheridan Center for Teaching and Learning

Credit: Finney County, Kansas. NASA/GSFC/METI/Japan Space Systems and US/Japan ASTER Science Team.

One of the most urgent global challenges we face is how to feed a growing human population.

The current estimated human population is a little more than 7 billion, but more than 9.5 billion people are expected to live on Earth by 2050.

2010 population 2050 population

Compounding the challenges of feeding this growing population is the fact that the amount of food each person consumes is also expected to increase. Currently, the global average daily caloric intake is about 2750 calories per person, but current estimates suggest that by the middle of this century that number will rise to more than 3000 calories per day.

To put this in perspective, in a single day the world's population consumes more than 1.9 trillion calories. By 2050 humans will consume more than 2.8 trillion calories every day, a 47% increase over current levels. That does not even include calories from crops that indirectly enter food supplies in the form of feed for animals whose meat humans consume; add them, and the planet's daily calorie requirements rise above 3 trillion.

2010 daily calories 1.9 trillion 2050 daily calories 2.8 trillion 2050 daily calories including feed crops 3.1 trillion

Before we can make decisions that help us better feed the world, we have to understand how and where we grow the food we eat today—and the consequences of that production.

We will begin this module with an exploration of modern agriculture: what we grow, where and how we grow it, and what effects it has on our environment. We will conclude with an exercise that illustrates how feeding the future population will be influenced and constrained by many factors, including our choice of diet, our agricultural practices, and even the availability of land and water.

What do we eat?

Although food production remains highly localized in some regions of the world, today agriculture takes place on a global scale.

When we look at global agriculture, we see that only a small number of crops account for nearly all of the world's food production.

If you were to guess, which crops would you say are the top three produced worldwide?

As you can see, even within this list of the top ten crops produced worldwide there is enormous difference between the top crop (maize) and the tenth most-produced crop (sorghum). In terms of total dry weight, there is relatively little difference between the top three crops—maize, rice, and wheat—but the production of each of these, individually, amounts to more than 2.5 times the production of the fourth crop on this list, sugarcane.

Agricultural production is often examined in terms of quantity—the total dry weight of a given crop. But there are many other ways to think about crops production. We could, for example, look at yield (amount per area), land area devoted to cultivating particular crops, or at the total number of calories each crop contributes to the global diet.

We'll look at some of these in more detail later. In particular, we'll consider yield, the amount of a crop produced for a given unit of cultivated land. For now, though, think of what we might learn about global agriculture by examining each of these different ways of quantifying agricultural production.

Examining production data for all crops and all countries can be overwhelming, so for most of this module we'll be focusing on just ten countries, shown below, and three major crops (maize, rice, and wheat). Exploring this limited set will allow us to probe some of the most pressing questions about modern agriculture and its environmental consequences. The countries and crops span a broad range of geography, climate, and adoption of modern agricultural technology.

Which countries are the biggest producers of maize, rice, and wheat?

Food production methods

We have a sense now of the major crops produced. In this section, we'll explore in more depth the different aspects of modern agricultural practices that contribute to the levels of production we observe for crops like maize, rice, and wheat.

The local, regional and global consequences of food production and are not altogether intuitive. We've already simplified it considerably by considering only ten countries. To further simplify, we'll consider just two different points in time, 1961 and 2012. Comparing data from these two years will allow us to observe clearly many of the big changes that have occurred in agricultural practices.

Let's start with yield.

What is yield? It's a measurement of the amount of a crop harvested from a given unit of cultivated land area.

What are some of the ways yield could be expressed?

  • Grams per square meter
  • Tons per acre
  • Tonnes (metric) per square kilometer
  • Bushels per acre
  • Hectograms per hectare

While all of these could be used to calculate yield, many agricultural data sources—including the Food and Agriculture Organization of the United Nations, whose data we're using to create many of the charts you see here—express yield as hectograms per hectare, both metric units.

A hectogram is a unit of weight equal to 100 grams, or about the weight of lemon or half of a large apple.


A hectare is a unit of area equal to 10,000 square meters, roughly equivalent to the size of a baseball field or the interior portion of an athletic track. For a local comparison, consider that the main green at Brown University is just slightly larger than one hectare.

Brown main green

Let's begin by taking a look at maize yields for our ten selected countries, comparing data from 1961 and 2012. Looking at the chart below, see if you can answer these three questions:

  • Have maize yields increased for all ten countries since 1961?
  • Has the increase in maize yields been the same for all countries since 1961?
  • Is the percentage change in yield a result of a change in the total area cultivated in each country?

Explore the data by selecting a different crop, or by looking at cultivated land area instead of yield. Use the buttons above the chart to update the chart.

What larger conclusions can we draw from this comparison?

Why did yields of maize, rice, and wheat all go up between 1961 and 2012?

Why have yields increased more rapidly in some countries and more slowly in others?

What changes occurred during this period in terms of agricultural practices?

Yields vary widely from country to country, as you have seen, but they have generally increased over time. One of the factors that explains how yields can increase also helps us understand the variations between countries or regions: farming methods.

Consider these two images of corn fields. The field on the left is low-yield, while the field on the right is high yield. In this particular example, the yield from these two fields can vary by a factor of ten: corn yield in the field on the right might be up to ten times higher than the field on the left!

Based on what you already know, or what you can guess, which of the following factors do you think contribute to high-intensity, high-yield agricultural practices?

  • use of synthetic fertilizers
  • use of pesticides
  • use of manual labor
  • high planting density
  • little or no pesticide use
  • use of irrigation
  • use of no fertilizer
  • use of heavy machinery
  • use of organic fertilizer

In several of the countries we're focusing on—first the United States and France, more recently Brazil and China —yields have increased dramatically over the past fifty years. These increases are the result of improved seed varieties and changing farming practices. Improved seeds include hybrids that produce higher yields, are more resistant to disease, and that can planted more closely together than older seed varieties. (Note the first genetically improved crop varieties were achieved through conventional breeding programs, but now are being created using using modern genetic techniques.) Other changes include the widespread use of synthetic nitrogen fertilizers, pest management using pesticides, extensive use of machinery, and the expanded use of irrigation. Taken together, these changes in modern agriculture are often referred to as the Green Revolution.

How intensely an area is farmed does give us some understanding of yield, but it is not the only factor that determines how much food is produced. The other critical piece to the story is how much land is dedicated to farming a particular crop.

We can look at these two factors together to understand the total production of a crop in a specific country or across several countries. The graph below plots the total land area dedicated to a crop (on the x axis) against the yield of that crop (on the y axis) for each of our ten selected countries.

Take a few moments to examine this plot, and to look at all three crops—maize, rice, and wheat.

The big producers of a given crop tend to fall on the higher end of yield and area. For example, the United States and China both devote around 35 million hectares to growing maize, and also have fairly high yields for this crop. (France has considerably higher yields, but cultivates far less land.)

This illustrates a simple but important principle: to increase total production, a country must either dedicate more land area to cultivating a particular crop, or it must increase the yield of the land area already used. Of course, a country can do both. If you look at the earlier chart of changes in yield and area between 1961 and 2012, you'll see that many countries have improved yields and expanded the area under cultivation. All such changes—whether to cultivated area, to yield, or to both—have consequences.

Environmental costs

What are the environmental costs involved in increasing the amount of land dedicated to agriculture or increasing yields on currently farmed land?

The amount of land that we have converted globally to agricultural uses is enormous. In fact, if you were to put all of this land together, it would cover the entire continent of South America. That's just for farms. Grazing lands cover an area the size of Africa. Together, our food production system uses about 1/3 of Earth's ice-free land surface.

Land converted to agriculture comes at the expense of other land uses, including natural vegetation. More farms mean less land in other uses. If we want to avoid deforestation or degradation of additional land while producing more food, we need to increase yields on currently farmed land. But what are the environmental costs of doing this?

We have mentioned in passing some of the farming practices that are involved in high-yield management. These practices can have severe environmental consequences.

Synthetic fertilizers: nitrogen and phosphorus

Nitrogen is a critical nutrient for plant growth and often limits agricultural production. Without nitrogen fertilizer, we could only produce food for half of the world's current population.

But adding nitrogen, particularly in amounts higher than plants need, can have a lot of negative environmental consequences. Nitrogen leaking into groundwater can make it dangerous for people to drink. Nitrogen leaking into rivers and estuaries can stimulate algae growth and lead to fish kills. Nitrogen gasses emitted from farm soils contribute to climate changes, stratospheric ozone depletion, smog and acid rain. These emissions go way up if fertilizer is applied in excess of crop demand.

Phosphorus, another key nutrient that has helped boost agricultural production, also causes harmful algae growth when it leaks into waterways. In addition, phosphorus ore is finite (like any mined resource—but not like nitrogen, which is abundant in air) and irreplaceable (unlike oil, which fuels modern farming and is finite, but can be replaced with other energy sources). Ore-grade phosphorus deposits are found only in a few countries; Morocco has almost 50% of the global total. The geopolitical implications of phosphorus distribution are only now starting to be discussed.

Pesticide and herbicide

Pesticides and herbicides are toxic by design. They are used to kill insects that might otherwise damage or destroy crops, or plants that compete with crops for space and/or nutrients. Residues of these pesticides can remain on food or enter surrounding ecosystems, potentially causing long-term health hazards to humans and other organisms.

We are still learning about the long-term effects of pesticide/herbicide exposure. For example, Atrazine, one of the world's most widely used herbicides, is now thought to be a hormone-disrupting pollutant. Roughly 75% of U.S. streams and 40% of U.S. groundwater wells contain Atrazine, which is now banned in the European Union.

Water use

Many areas of the world are experiencing or will experience water scarcity because freshwater that is suitable for human consumption is a finite resource. Much of the available water is now being used to irrigate crops. Globally, almost 70% of available freshwater is used for agriculture.

Irrigation allows for much higher yields in water-scarce regions. Over the long term, however, overuse can lead to soil salt accumulations that render the soils unproductive. Using groundwater faster than it is replenished (common in arid regions with irrigated agriculture) is inherently unsustainable. Even in fairly wet regions the diversion of water has myriad effects on aquatic ecosystems.

Now let's consider how some of the agricultural methods associated with high-yield practices have changed over the past fifty years. The graph below shows several indicators—including fertilizer, pesticide, and water use—for our selected countries. While many of these indicators aggregate data (for example, fertilizers of all types are shown), you can still observe some general trends when comparing these countries.

As you can see, some of the data in this graph are incomplete. If you were trying to determine whether these various indicators are related to one another—for example, if you wanted to know whether high use of fertilizers and high use of insecticides tend to be correlated with high agricultural yields in these countries, what other data might you want to collect? How would you want to examine it in order to show a correlation?

Take some time to explore the vast quantity of agricultural and food-related data available from the Food and Agriculture Organization of the United Nations. You can browse many different categories of data and visualize some of the data sets directly from the FAO statistics portal.

Can we feed our growing population?

By 2050, the global human population is expected to exceed 9 billion. Using that estimate, let's consider in this final section some of the challenges facing us in the future.

The chart below shows the current global calorie production from crops as a product of the total land area used for food production and the total calories produced per unit of land.

The blue circle represents 2014 estimates for the current global diet: roughly 50 million km² are used for agricultural production worldwide; on average, about 180 million calories are produced per km2 each year. However, only **15 million km2** of this area are currently cultivated as cropland. The remaining 35 million km2 are used as pasture.

Note what happens when you select the Cropland Only option. This shows a hypothetical scenario in which only existing cropland is used to produce food. How much does land area drop? How much does caloric yield (calories per area) change? What is the percentage of calories that come from the 35 million square kilometers (the size of Africa) we currently use to graze animals?

Now consider the world's future food needs.

The gray curve in this plot represents possible land and production requirements for the projected population of more than 9 billion people in the year 2050. Clicking on this curve will calculate the land area and caloric yield of that particular point—in other words, how many calories would be produced for a given land area and average yield. Click on a few different places in the curve. Is one region a "better" alternative? Why? If you had to break this curve up into different pieces that had different costs or benefits, what portions the curve would you group together?

As you may have observed already, there are three categories of options for producing the food needed to feed the world's population in 2015

  1. Increase the number of calories produced on today's farms
  2. Increase the area devoted to farming
  3. A combination of both (increased land use and yield)

Let's explore each of these options.

Increasing yields where they are already high

In some places, such as the United States, Western Europe, and parts of Asia, food production has increased dramatically over the past half century because of Green Revolution technologies. In these areas, yields are almost as high as our current state of knowledge allows, and yields are growing slowly (about 1% annually).

Yield of wheat in the United States since 1961

Consider this graph of wheat yields in the United States since 1961.

  • How long will it take for yields to grow by 70% if yields increase by only 1% a year?
  • What approaches do you think would help increase yield growth rates?
  • How might climate change impact the ability of farmers to increase yields?

Increasing yields where they are low

In other places, such as sub-Saharan Africa, yields are much lower than they could be if Green Revolution technologies, such as hybrid seeds and fertilizers, were readily available. The vast majority of the world's 800 million undernourished people live in sub-Saharan Africa and South and East Asia.

The map below is a crude estimate of the yield gap for maize—the difference between how much is currently being produced in a place relative to what could be produced using the most productive technology (year 2000 estimates). Green shading indicates high productivity, while yellow and red indicate production is 50% or less than what it could be.

World map shaded to show yield gap

  • Why are yields so low in sub-Saharan Africa and Southeast Asia?
  • What are the adverse consequences of Green Revolution technologies?
  • Do the benefits of Green Revolution technologies outweigh their costs in regions with low productivity?

Increasing land area

The second option for increasing total calories produced is to devote more land to agriculture. Farming currently occupies about 15 million km2. Pastures and grazing lands occupy another 35 million km2, an area roughly the size of Africa.

Grazing lands are by far the most extensive human use of land, but "grazing land" is not a monolithic category. Cattle graze in the former Amazon rainforest, the deserts of the American west, the windswept Pampas of Argentina, and just about everywhere else you can imagine.

Here's the amazing thing: all that grazing land produces less than 10% of our total food calories.

As we think about converting more land to intensive cropping, grazing lands are a reasonable place to start. But the barriers are many. In some places, grazing is relegated to places too dry, too steep, or too rocky to support farming (think about grazing in the Rocky Mountains). In other places, land owners (or renters) don't have access to capital, so they can't invest in farm equipment, seed, or fertilizer. Animals reproduce themselves and can be an efficient way to gather calories from an otherwise inhospitable landscape with relatively low labor costs.

One area where Brown students have worked is in the mountains of Southern Costa Rica. Deforestation here started in the 1950s. The steep topography confines industrial agriculture to large river valleys, which are now covered by oil palm, pineapple and banana plantations. The rest of the landscape is covered by forest patches, small scale coffee farms, a smattering of other crops, and lots and lots of pastures.

Cows quickly erode the topsoil. This image of ENVS MS Student Tim Huth, who is 6'8", standing at the bottom of a hill rutted by cows, provides a sense of how much soil can erode even in pastures that are only a few decades old. Because the land is so steep, however, intensive agricultural production is impossible. And after a few decades of cattle-induced erosion, crop production isn't really possible either.

Tim Huth at bottom of hill rutted by cows in Costa Rica

Credit: Stephen Porder

Currently, 36% of global crop production goes to feed animals, and only 12% of the calories in that feed end up in human mouths. Another 9% of crop calories go to biofuel use, which is predicted to increase dramatically in coming decades. Thus, no more than 60% of calories from the crops we grow actually feed humans. Only 4% of the calories we feed to cows end up as beef calories we eat - thus cutting meat consumption is perhaps the single biggest thing a person can do to reduce their environmental impact. We'll come back to this later.

Graphic composed of 100 small blocks shaded to represent percentages of crops used for biofuels, animal feed, and human consumption

Source: Cassidy et al. Environmental Research Letters 2013.

With all this in mind, let's consider a future scenario in which agricultural yields continue increasing slowly, meaning that the only way to produce enough calories to meet global needs—assuming no change in the current global diet—is to increase land devoted to agriculture to approximately 85 million km2, a 70% increase above current levels. Where would you find this land?

This graph represents all land on Earth according to biome. (Biomes that make up less than 1% of total land area have been omitted.) The red regions of each bar (to the left of the grey vertical line) indicate land that is already used for food production—either as pasture or as cropland. The lighter region of each bar shows the current remaining land area of that biome.

To select land for future agricultural use, click and drag to the left any of the bars corresponding to biomes. Continue until you have selected enough new agricultural land to meet 2050 calorie needs. The first time you click on a biome, a description of that biome will appear. For the purposes of this exercise, large scale expansion of agriculture in certain biomes is not permitted.

km2 used
km2 needed


This module has introduced several key challenges to sustainably feeding a growing population. We've explored the trade offs between intensifying land use and using more land. But there are several other points worth considering.

The challenge of maintaining the global food supply, like many of the challenges we explore in this class, is so big as to be overwhelming. How can science help us address the fact that we graze animals on an area the size of Africa?

The answer is that the challenge of feeding 10 billion isn't one challenge, it's thousands of challenges each of which may well have a tractable solution. And science, even basic science that may not at first seem relevant, has a lot to offer in overcoming those challenges.

Take, for example, the problem of feeding animals. Many countries—the US first and foremost—have incredibly inefficient food production systems because we feed crops to animals, and only 4% of the crop calories end up as calories we eat. But we don't just feed crops to animals. Pigs, for example, are fed a lot of fish meal (mostly ground up anchovies). It's an incredibly rich protein source. But anchovies and other feed fish are near the base of the ocean food chain - their stocks are threatened by our fishing fleets. And they are mostly used as feed for animals.

Humans currently dedicate 35 million square kilometers (roughly the size of Africa) to grazing animals. This is the single largest human land use. Yet those pastures produce fewer than 10% of our calories. Meat is an important protein source for many people. Pastures are often land that is not very good for farming. But even given those considerations, it's worth thinking carefully about meat production/consumption in the future.

Many people are asking whether there is a better way - and many have turned to insects as a potential high-protein source that could be grown to feed animals in lieu of wild caught fish or soy beans grown on what used to be the Amazon forest.

One researcher, Dr. Phil Taylor, is a scientist at Duke University. Dr. Taylor had an idea that food waste could be used to raise insects that in turn could be used for animal feed. He is not an entomologist. Nor is he a food scientist. But he saw two problems—food waste and the need for high protein animal feed—and used what he did know to ask a simple question: what's the most efficient way to produce insects (in this case black soldier flies, also known as maggots) from food waste?

We haven't talked about it in this module, but food waste is a major loss of crop production as well. Estimates vary, but by some calculations 40% of all food produced never gets eaten. In wealthy countries the food is purchased but not used. In poorer countries lack of adequate transportation and refrigeration means food spoils before it reaches the buyer. Either way, that's a big loss to the system.

Image of fresh food in garbage can to illustrate food waste

Credit: USDA. CC BY.

His hypothesis, after reading about the basic biology of the insects, was that the light environment was important for insect reproduction. Soldier flies are rainforest animals with eyes sensitive to a very wide range of light, and the light in the rainforest is quite different from the lab in which he was raising flies. So he set up a hatchery and exposed groups of 1000 flies (500 male, 500 female) to different light environments. And then he counted the number of eggs deposited.

Experimental black soldier fly hatchery used to determine optimal light environment for reproduction

Credit: Philip Taylor, Duke University.

Here are some of his data. Which light environment worked best?

Data from Philip Taylor's hatchery experiment, illustrating effect of light on black soldier fly reproduction.

Source: Philip Taylor, Duke University

Based on the observation, Dr. Taylor did some analyses of the insects, and determined that they were actually quite efficient at turning food waste into biomass.

Graphic illustrating black soldier fly conversion of food waste into fat, meal, and frass. The image shows that 100 kg of food waste yields 3.5 kg of fat, 5 kg of meal, and 20 kg of frass.

For every 100 units consumed, black soldier flies produce 3.5 units of fat, 5 kg of meal, and 20 kg of frass, which can be used as fertilizer.

Credit: Philip Taylor, Duke University.

But don't take our word for it—watch this time lapse video, which in real time took 3 hours.

Credit: Philip Taylor, Duke University.

Many think that a teeming trough of maggots is disgusting. I think plucking entire populations of fish from the ocean to the point of exhaustion is far more disgusting.

Phil Taylor

Source: Philip Taylor, Duke University

Based on his experimental work, Dr. Taylor performed some basic calculations, not unlike the ones we've asked you think about in this module:

  1. How much food waste is produced in the world?
  2. How many fish are caught to feed animals?
  3. How many insects would be needed to replace that feed?

The answer is surprising. If we used 6% of global food waste to raise insects for animal feed, we could replace all the wild caught fish currently fed to animals. That's still a global view, but there is no reason not to start.

Graphic illustrating diversion of 6% of global food waste.

Dr. Taylor is working with supermarkets and farmers (and the FDA) to implement this process. It's a long road to a small part of a solution. But at its core is basic science, experimentation, and creative thinking. In all likelihood, that's where most solutions come from.

Credit: Philip Taylor, Duke University

Obviously insect protein raised on food waste isn't the whole answer. But we need many such creative solutions if we're going to feed 10 billion people. And even more if we're going to do it sustainably.

There are many such partial answers. Dr. Lisa Schulte-Moore is working on reducing nutrient pollution from intensive agriculture while increasing habitat for native prairie species.

Dr. David Lobell is working on how climate change may impact the food supply to the most food insecure people on earth.

Dr. Cheryl Palm is working to understand how food production can be increased in sub-Saharan Africa, a region that stands for low crop productivity and chronic food scarcity.

Here at Brown, we are trying to understand the role developing nations will play in the global commodity supply, and the costs and benefits of countries like Brazil and India emerging as globally important hubs of food production.

Hundreds, if not thousands, of other scientists are doing basic science: raising insects, developing better soil maps, working on regional climate projections, and many many more projects to understand how to meet the challenge of feeding 10 billion. Perhaps you will be one of them. It is certainly a problem that needs everyone's attention.