Today we recognize that environmental problems are a worldwide concern. Poor agricultural practices in Africa and China result in dust storms that affect the local people and are also carried to the rest of the world. Concern about global warming has led to the convening of international conferences and the drafting of treaties whose goal is to reduce the impact of energy use. Many are concerned about protecting endangered species and the forests, grasslands, and oceans that provide habitats for them. In many ways these problems are the result of an incredible increase in the size of the human population. As the human population has increased, humans have sought to use land for agriculture and other purposes. Converting land to agricultural use results in its loss for other purposes such as habitat and watershed protection. In order to understand the nature of environmental problems and steps we can take to solve them, we need to be familiar with some of the central ideas of the science of ecology.