Introduction

The planet Earth is huge. It has a surface area of about 510,000,000 sq.kilometers of which nearly 30% is dry land. The planet has life giving air and water, supporting a wide range of plants and creatures. About 10% of dry land can be used to grow crops, 20% can be grazed by animals, and about 27% is forested. In these types of environment, humans have thrived for many thousands of years. The number of people in Earth now has reached nearly 6,135 million. By the year 1050 it may have soared to 9,030 million. Parts of our planet are becoming overcrowded and people need land, minerals such as oil and ever increasing amount of food and water. These needs greatly affect the natural world. Humans clear forests, drain wetland and pollute rivers,oceans,soil and air. It is predicted that such interference will change the global climate. In many ways the future is very uncertain.