The principle of "common but differentiated responsibilities" is the cornerstone of the United Nations Framework Convention on Climate Change (UNFCCC), formed in 1992 and now ratified by 192 countries.

The principle serves as an important reason why the world's countries, all with many differences in their respective interests and concerns, could sit down together to negotiate a solution for the pressing issue of climate change.

The word "common" shows that fighting climate change is an obligation for every country around the world.

Undoubtedly, when the earth, mankind's common homeland, is facing a crisis, people around the globe must work together and help each other to find a solution.

However, let us not forget that the responsibilities are not only "common" but also "differentiated."

The industrialized countries, with abundant financial resources and advanced technologies, should shoulder their historical responsibilities and make tangible moves to deal with their high per capita carbon dioxide emissions.

As for the developing countries, "economic and social development and poverty eradication are the first and overriding priorities," the convention said.

Taking into full consideration the different socio-economic contexts, historical responsibilities, and per capita emissions of various countries, the convention stipulates that: developed countries should take the lead in combating climate change and provide financial resources, including the transfer of technology, for developing countries.

With the funds and technological support provided, developing countries need to adopt measures to mitigate and adapt to climate change, according to the convention.

In 1997, the third session of the Conference of the Parties to the UNFCCC held in Japan adopted the Kyoto Protocol, which, for the first time in history, made the principle of "common but differentiated responsibilities" become a legally binding commitment.

The United States, reluctant to accept the principle, has not yet ratified the protocol.

During negotiations in recent years, some developed countries, including the United States, have expressed dissatisfaction with the principle, demanding that developing countries also commit themselves to the binding targets on emission cuts.

Why, then, don't some developing countries such as China, India and Brazil, also major carbon emitters, have to commit themselves to the legally binding targets on emissions cuts?

The reason is that the per capita emissions of those countries are far less than those of the developed ones, and they have produced only "survival emissions" instead of "luxury emissions."

More importantly, the carbon dioxide currently in the atmosphere was mostly produced during the industrialization process of the developed countries.

It is worth noting that carbon dioxide, the primary greenhouse gas, has an atmospheric lifetime of between 50 to 200 years.

That means that the carbon dioxide discharged by Western countries during the Industrial Revolution period some 200 years ago still remains in the atmosphere.

As the convention said: "The largest share of historical and current global emissions of greenhouse gases has originated in developed countries," and "per capita emissions in developing countries are still relatively low."

Though the collective carbon output produced by developing countries has grown significantly in recent years, it is still quite low compared with the unchecked emissions produced by the industrialized countries during the past 200 years.

The developing countries, however, should also take initiatives to address global warming and strive to not advance their economies at the cost of the environment, like most of the developed countries did.

To this end, many developing nations have recently put their emission targets on the table.

One thing, however, must be made clear: under the principle of "common but differentiated responsibilities," the emission cut targets are a legally binding commitment for the developed countries, while the measures and objectives set by the developing ones are their voluntary actions.

(Xinhua News Agency December 6, 2009)