Common But Differentiated Responsibilities

Common But Differentiated Responsibilities (CBDR) was formalized in United Nations Framework Convention on Climate Change (UNFCCC) of Earth Summit in Rio de Janeiro, 1992. The CBDR principle is mentioned in UNFCCC article 3 paragraph 1.., and article 4 paragraph 1. It was the first international legal instrument to address climate change and the most comprehensive international attempt to address negative impacts to global environment. CBDR principle acknowledges all states have shared obligation to address environmental destruction but denies equal responsibility of all states with regard to environmental protection.
In the Earth Summit, states acknowledged disparity of economic development between developed and developing countries. Industrialization proceeded in developed countries much earlier than it did in developing countries. CBDR is based on relationship between industrialization and climate change. The more industrialized a country is, more likely that it has contributed to climate change. States came to an agreement that developed countries contributed more to environmental degradation and should have greater responsibility than developing countries. CBDR principle could therefore be said to be based on polluter-pays principle where historical contribution to climate change and respective ability become measures of responsibility for environmental protection.
Concept of CBDR evolved from notion of "common concern" in Convention for the Establishment of an Inter-American Tropical Tuna Commission of 1949 and "common heritage of mankind" in United Nations Convention on the Law of the Sea, 1982.
Objectives.
In general, there are three objectives of contracting differential treatment; to bring substantive equality in a framework for justice, to foster cooperation among states, and to provide incentives for states to implement their obligations.
In the Earth Summit, CBDR principle was established to apprise that the pollution is beyond boundaries and to achieve environmental protection through means of cooperation. UNFCCC 1992, Article 3 paragraph 1, "The Parties should protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities. Accordingly, the developed country Parties should take the lead in combating climate change and the adverse effects thereof."
Background: Differential Treatments.
CBDR was not the first differential treatments of countries in international agreements. There were other protocols, agreements that employed principle of differential treatment. 
Criticism.
Todd Stern, U.S. Special Envoy on Climate Change said in commencement speech at Dartmouth's 2012 graduation ceremony that world now can no longer have two distinct categories of countries having different responsibility. Countries should instead follow differentiation of a continuum, where states are required to act vigorously according to their own circumstances, abilities and responsibilities. He emphasized in having common responsibility for all countries instead of a group of countries taking a dominantly more responsibility.
Stone argues meaning of a word 'differentiated' could be problematic as every agreement differentiates. He also says CBDR is "neither universal or self-evident"
Cullet points out that with CBDR, it may be difficult to determine the existence of specific customary norms
Rajamani says developing countries would have an unfair economic advantage because they do not face same restrictions like developed counties. Climate Change Treaty would be ineffective without developing country participation. US has been suggesting key developing countries are not doing enough to satisfy 'common responsibility for the problem' but developing countries emissions from their is'survival emissions' and that of the developed countries are 'luxury emissions'