Page "Environmental law" Paragraph 16

Customary international law is an important source of international environmental law.

These are the norms and rules that countries follow as a matter of custom and they are so prevalent that they bind all states in the world.

When a principle becomes customary law is not clear cut and many arguments are put forward by states not wishing to be bound.

Examples of customary international law relevant to the environment include the duty to warn other states promptly about icons of an environmental nature and environmental damages to which another state or states may be exposed, and Principle 21 of the Stockholm Declaration (' good neighbourliness ' or sic utere ).