You need to use the scientific method and

In order to work as an environmental scientist.

You need to use the scientific method and knowledge of the environment in order to work as an environmental scientist.

Explanation:

An environmental scientist should have an excellent knowledge about the systems of the environments and scientific methods. If a scientist is thorough about his understandings of the environment, he will be able to recognize any changes in the environment immediately and formulate the necessary reasons for the changes by using the scientific method of research. By using the scientific method of research, a scientist is able to learn about the various phenomenon occurring in the environment.