The ENMOD Convention (full name, Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques) signed in 1977, began as a response to outcry following the controversial use of Agent Orange. Its main goal was to prevent militaries from widespread destruction of the environment, similar to that done by the United States in its use with Agent Orage in the Vietnam War. The United States signed onto the original convention treaty, and nearly 70 countries have signed on to date.
Of interest to the policy debate on geoengineering is the clause that regulates the use of technology on a global environmental scale. Article 1, Section 1 states, “Each State Party to this Convention undertakes not to engage in military or any other hostile use of environmental modification techniques having widespread, long-lasting or severe effects as the means of destruction, damage or injury to any other State Party.” To elaborate, Article 2 states, “As used in Article 1, the term ‘environmental modification techniques’ refers to any technique for changing–through the deliberate manipulation of natural processes–the dynamics, composition or structure of the Earth, including its biota, lithosphere, hydrosphere and atmosphere, or of outer space.”
Fascinating–this document, agreed upon by almost eighty countries–explicitly states that no part of the earth system can be deliberately altered through human intervention. This would appear to prevent any attempts at geoengineering, which usually involve alteration to the hydrosphere and atmosphere, from occurring. It at least has laid a platform that if geoengineering were to be implemented, an international convention similar to the one that created ENMOD would be needed to establish consensus to override ENMOD in situations.
However, it is interesting to note that Germany and India recently performed a geoengineering experiment in the Indian Ocean. Both have signed on to ENMOD.