"Principle 15
In order to protect the environment, the precautionary approach ( http://globalskywatch.com/chemtrails/ubbthreads.php?ubb=showflat&Number=17984#Post17984 , Denglisch) shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation."
http://www.jus.uio.no/lm/environmental.development.rio.declaration.1992/portrait.a4.pdf page 3f


Legal Binding of "the precautionary approach" through "Decisions" within die UN body of the "Convention on Biodiversity":
http://globalskywatch.com/chemtrails/ubbthreads.php?ubb=showflat&Number=17974#Post17974


Legal value of a "declaration":
https://treaties.un.org/pages/overview.aspx?path=overview/glossary/page1_en.xml#declarations


Legal value of the term "declaration" in the Rio Declaration:
" (...) However, declarations are not always legally binding. The term is often deliberately chosen to indicate that the parties do not intend to create binding obligations but merely want to declare certain aspirations. An example is the 1992 Rio Declaration."
https://treaties.un.org/pages/overview.aspx?path=overview/glossary/page1_en.xml#declarations