This momentum is directly related to the current young age distribution of the people in most countries, and is responsible for the continued population growth that would still occur with a potential change to 2.1 children per couple. Clearly, national populations with a median population age of only 16 years will continue to grow and increase for the full 70 years. With more people on earth, more food, more water, more shelter, and more jobs will be required. As the human population expands, it spreads farther than ever before over the land with houses, roads, industries, and other activities. In this process, prime cropland, fresh water, and other vital resources for food production are compromised.
Food production requires fertile cropland, freshwater, and sunlight.
Successful agriculture also requires both renewable and fossil energy for cultivation, fertilizers, pesticides, and irrigation. Each year, more than 10 million hectares of cropland are degraded and lost because of wind and water erosion. Erosion is intensifying worldwide, especially in developing countries where the rural poor remove crop residues for cooking fuel. Valuable forests are being removed for new cropland, while often poor farmers are cultivating marginal, unproductive lands. In arid regions, farmers must use irrigation water.