Most scientists believe that the increase in greenhouse gas emissions caused by human activities is a major cause of global warming. Unchecked carbon emission growth will lead to disastrous changes that threaten human welfare.

Nearly 200 nations are trying to work out an agreement on methods to combat global warming, although negotiations are stalled. Whatever plan is eventually adopted is expected to be based on the universally accepted principle of "common but differentiated responsibilities".

Developed countries are responsible for about 80 percent of carbon emissions put into the atmosphere since industrialization, so they are urged to play a major role in curbing global emissions.

Their responsibilities, besides meeting quantative and legally binding carbon emission targets, also include providing financial and technological help for developing nations, so they can emit less carbon dioxide during their course of economic growth and urbanization.

Developing countries, which are still relatively poor, do not bear mandatory targets to mitigate their carbon emissions. However, they are asked to take domestic steps to slow the increase of their carbon footprints.

The European Union is the most active in tackling climate change, partly in a bid to keep its competitive edge on clean technologies. Other developed countries are moving slowly because reducing carbon emissions will mean sacrificing economic growth.

China, as a developing country, is exempted from the obligations to cut carbon emissions. Instead, it has set targets to reduce carbon intensity - the carbon emissions for each unit of economic growth.

China also faces increased international pressure because it has the world's second largest economy and is one of the world's top greenhouse gas emitters, although its per capita emissions are still quite low.