I can identify and recognize the 4 spheres and their interdependence.
I can explain how human activities impact our planet in each of the spheres.
Between 1959 and 1999, the human population on Earth doubled from three billion to six billion. By 2042, there will be nine billion people. They will all need homes, food, clean air, and clean water.
Our planet is 8,000 miles in diameter, but our atmosphere, the layer of air in which we live, is only about five miles wide. All life is crowded into this thin envelope of air.
During the 1990s, carbon dioxide emissions increased approximately 1.3% each year. But since 2000, the rate has increased to 3.3% per year. Annual global emissions of this greenhouse gas increased 35% between 1990 and 2006.
Not all the news is bad. During the 1960s and 1970s, the United States passed a series of clean air and water laws. Since then, the amount of soot and other particles in the air has dropped. The actual health of our atmosphere has improved in our cities and towns.