Why have issues related to global environmental protection become the priority concern of states since the 1990s?
Issues related to global environmental protection became a priority concern of states since the 1990s because the 1992 Earth Summit in Rio de Janeiro firmly consolidated the focus on these issues. This summit brought environmental concerns to the centre-stage of global politics, attended by 170 states and numerous NGOs.
Furthermore, the Brundtland Report of 1987 had highlighted that traditional economic growth was unsustainable. By the 1990s, the awareness of environmental consequences had acquired a political character, urging states to address the critical relationship between economic development and environmental management.
Explanation
The answer is derived from the textbook context which states that the growing focus on environmental issues was 'firmly consolidated' at the 1992 Earth Summit (Rio de Janeiro), bringing them to the 'centre-stage of global politics'. Additionally, the context mentions the 1987 Brundtland Report's warning about unsustainable growth and the fact that environmental awareness had acquired a 'political character' by this time.