The Rome Statute of the International Criminal Court is the governing document which sets out the existing international Crimes. Ecocide was to be included in earlier drafts, until it was removed in 1996. You can read about ecocide law history here and download the The Human Rights Consortium research paper “Ecocide is the missing 5th Crime Against Peace“.
The proposed amendment to the Rome Statute was submitted by Polly Higgins to the United Nations Law Commission in March 2010. A full legal reasoning for a law of ecocide and the definition was laid out – you can read what was submitted in Chapters 5 & 6 of Polly Higgins’ first book, Eradicating Ecocide. Polly Higgins proposed as an amendment to the Rome Statute that ecocide be legally defined as
the extensive damage to, destruction of or loss of ecosystem(s) of a given territory, whether by human agency or by other causes, to such an extent that peaceful enjoyment by the inhabitants of that territory has been or will be severely diminished.
This definition informs the draft amendment to the Rome Statute which is currently being worked on by international criminal law experts.
There are currently 122 nation States that are signatories to the Rome Statute.
Amendments to the Rome Statute of the International Criminal Court must be proposed, adopted, and ratified in accordance with Articles 121 and 122 of the Statute (you can download core ICC texts here). Any State Party to the Statute can propose an amendment. Adoption of the proposed amendment is by a two-thirds majority vote in either a meeting of the Assembly of States Parties or a review conference called by the Assembly. An amendment comes into force for all States Parties one year after it is ratified by seven-eighths of the States Parties.
Any amendment to articles 5, 6, 7, or 8 of the Statute (the crimes) only enters into force for States Parties that have ratified the amendment. A State Party which ratifies an amendment to Articles 5, 6, 7, or 8 is subject to that amendment one year after ratifying it, regardless of how many other States Parties have also ratified it. (Article 121(5)) For an Article 5, 6, 7, or 8 amendment, the Statute itself is amended after the amendment comes into force for the first State Party to ratify it. (Article 122(2))