 The population of the earth is currently over 7 billion people. The United Nations estimates the world population will be between 8 and 10 billion by the year 2050. All of these people need to eat. They need clean water to drink. They need fuel. They need materials. And they produce waste. More people are buying and driving cars. As population increases, we build more roads, houses, schools, and we install and use more electricity. We heat buildings in cold areas, and we use air conditioning in hot areas. All of these activities need energy. So we burn wood, coal, oil, and natural gas. When we buy and use products, we produce garbage. Garbage may be the old broken products or the packaging. Plastic, batteries, and electronics contain toxic chemicals and metals like chlorine, mercury, and lead. When we put this garbage into the ground, those chemicals may leak into the ground and water. Extracting and burning fuel pollutes our water, air, and soil. Garbage and chemicals pollute our water, air, and soil. We have a very limited amount of fresh water to drink and cook. Water pollution also affects fish. It can kill fish, or the fish may eat the chemicals and plastics, which then go into our bodies when we eat the fish. And we are catching too many fish. We may soon run out of some popular species. So, do we have enough natural resources for 9 billion people? 9 billion shoppers? 9 billion cell phone users? 9 billion drivers? 9 billion hungry people? To make cars and cell phones and computers? We also need metals. Do we have enough steel? Enough copper? Enough gold? Enough aluminum? We mine phosphorus, a mineral, to make fertilizer. Finally, as we burn more fuel, the temperature of the ocean is increasing, and our weather is changing. Many people live in cities on the coast. If the temperature increases, the ice at the north and south poles of the planet will melt. It's already melting. And as the ocean levels rise, many cities, as well as some island nations, may flood. What can we do about these environmental problems? What can we do to manage and share our limited resources? What can we do with the one planet that we all need to live so that our children and grandchildren can also enjoy clean air, clean water, and a good standard of living? This is a challenge for scientists, for governments, and for every one of us.