People have continuously managed to grow more food. Over the years, farmers and scientists have discovered ways to grow crops stronger, bigger, and faster. This has drastically increased in the amount of food we produce.

These huge increases in food have allowed the world's population to grow. In fact, it has quadrupled over the last century. As the population grows, so does the amount of space that we need to feed people. In 2016, farmers used more than seven million square kilometers (2.7 million square miles) to grow corn, wheat, rice, and other grains. That's nearly half of all cropland on the planet.

In the coming decades, feeding a growing population will become more difficult. Greenhouse gases are heating the planet. This has led to an increase in droughts and heavy rains. These changes in global climate—known as climate change—may make growing food more difficult.

Modern agriculture is also partly responsible for its own problems. Farmers often use methods that are not sustainable. Farming sustainably means not using too many of Earth's natural resources or harming ecosystems. It ensures that future generations can meet their needs too. Sometimes, farmers are only able to grow a lot of food in ways that harm ecosystems.

There are many ways in which agriculture harms ecosystems. Three main ways are irrigation, animal grazing, and chemical fertilizers.

Irrigation
Worldwide, 70 percent of the freshwater that people use goes to agriculture. Much of this water is used for irrigation, or the process of watering crops through pipes, canals, and sprinklers. Irrigation is necessary for growing a lot of food. Experts think that agricultural water use will need to increase 15 percent or more by 2050. It will have to increase to feed the growing population.

Irrigation has consequences for the environment. One major consequence is draining water out of rivers and underground water systems. Irrigation can also cause floods, which create soil conditions that poison plant roots. In areas where water has been drained, the soil can become too salty. This also harms plant growth.

Irrigation also increases water evaporation, or the process that turns liquid into gas. This affects air temperature and pressure. It also affects moisture in the air. Studies have shown that irrigation can change rainfall thousands of kilometers away from the irrigated areas.

Animal Grazing
A huge amount of agricultural land is used for cows and other animals. In the western United States, hundreds of millions of acres are set aside for animal grazing. When animals graze, they eat grass in pastures.

Farm animals are responsible for a large part of greenhouse gas emissions. Greenhouse gases trap heat in Earth's atmosphere. This causes the Earth to warm. Methane and carbon dioxide are two major greenhouse gases. Cows and their manure are responsible for releasing huge amounts of methane. Land use and destruction also lead to the release of carbon dioxide into the atmosphere.

In addition, overgrazing is a major problem for environmental sustainability. In some places, land is grazed so heavily that grasses are unable to grow back. Their root systems can get very damaged. Certain types of native plants might die off.

Cows often concentrate near streams and other waterways. Together, overgrazing and cow waste can pollute water sources. Cows can also destroy soil. Then, the soil gets swept away by wind and water.

Chemical Fertilizers
Modern agriculture depends on chemical fertilizers. These are compounds that farmers spread over crop fields or into dirt. They contain nutrients that plants need to grow, such as nitrogen and phosphorus.

Chemical fertilizers have helped double how much food we can produce. But they have also increased nitrogen and phosphorus levels in the environment. About half the nitrogen in chemical fertilizers escapes from crop fields. It finds its way into the soil, air, and water.

Large amounts of nitrogen and phosphorus harm ecosystems. Ecosystems become loaded with too many nutrients. This causes algae, or water plants, to grow in water bodies. This process is called eutrophication. When the algae decay, they use up the oxygen in the water. This leaves very little oxygen for other plants and animals in the water. These areas of little to no oxygen are called "dead zones" because organisms die without oxygen.

As the population continues to grow, it might become more difficult to feed people. We will likely have to find more sustainable ways of farming.