How Would We Know If an International Norm on Pollution

How would we know if an international norm on pollution existed?

A) If an international body exists to prevent international pollution.
B) If a president of a democratic country is voted out of office for polluting the environment.
C) If a country faces international repercussions for polluting the environment.
D) If there exists an international law detailing how states are not supposed to pollute.
E) If a few states in the international system refuse to pollute the environment.