Context IEL
Any society requires law (Hobbes, Rousseau, etc…) same for the International Society. Therefore we have laws produced by it to organise its internal relations, born in 1648 with the conclusion of the Peace of Westphalia after the 30 years war. This new international political order was based on sovereignty, as the 30 years war was not only a religious confrontation but a political one (feudalism vs. absolutism).
Effect of Westphalia
The absolutist perspective surviving, a system made up of sovereign individual nations (independent inside and outside its borders) was created. With this change, the need for new principles and rules came. This gave birth to international law. The linkage is strong, IL was necessary to preserve state sovereignty. Indeed, the objective of IL was good neighbouring relations, so coexistence, between states. In this way, one state would not interfere in the internal affairs of another sovereign state.
This gave way to a system of laws where non-intervention became the sacro-saint principle. There was little intervention in the affairs of states, or what they did, outside of what pertained to the independence of their equals. Most affairs, they regulated and enforced themselves domestically.
Consequences today
States could do whatever, and IL wouldn’t do anything (crimes against humanity, war crimes, etc…). This would include the pollution of the environment or the destruction of its biodiversity among its perverse consequences, but also unlimited GHG emissions… and many others pertaining to the environmental dilemma we face today. The first waves of GHG emissions, came in the era where IL was a law of coexistence.
From the beginning of the second half of the 20th century, after WW2, there was a shift to a law of cooperation. Therefore, these consequences changed. There was a factual factor (it was realised that a fact in international life was that no state acting alone can achieve its goals→e.g. trade, invest, mitigate climate change, etc…). Many problems are inherently transboundary and therefore international.
Cooperation today
Paradoxically cooperation is most important today when states are threatened in their existence by environmental crises (climate, biodiversity and others). This is specially the case for SIDs, which will disappear without cooperation. The development of any state (human-wise, technologically, politically, etc… but specially ecologically) independently of its characteristics is deeply tied to cooperation.
And it cannot happen in a vacuum, nor can it without a framework and a certain stability. This, which guarantees and facilitates cooperation, is specifically what IL brings to the table along with predictability. We could therefore define it as a legal framework which governs the interactions between its subjects for the purpose of cooperation in our contemporary world.
Right now, states cooperate in all fields of human activity and as such, IL has been complexified or expanded. The one pertaining to the environment is International Environmental Law.