Two environmental slogans. 1972 The human environment conference convened by the United Nations put forward two environmental slogans: there is only one earth and the Declaration of the United Nations Conference on Human Environment. 1972 16 On June 5 and 6, the United Nations held a conference on the human environment in Stockholm, Sweden, to discuss the environmental problems in the contemporary world and explore strategies for protecting the global environment. This is the first conference in human history to study and protect the human environment in the world.