Anything related to reducing greenhouse gas emissions is grabbing global attention as the Copenhagen climate change conference draws nearer.

"Carbon tariffs" is just one on the hot words list. But the attention it attracts lies more in the controversy it causes rather than how it could help with environmental protection.

In June, the U.S. House of Representatives passed legislation on climate issues that contained carbon tariffs, which would allow the president, beginning from 2020, to impose duties on imports of carbon-intensive goods such as steel, cement, glass and paper from countries that have not taken measures to cut their own emissions, provided the U.S. has not joined any multilateral emissions agreement by then.

However, the decision has triggered wide debate on whether the U.S. would use the legislation to provide environmental protection or trade protection.

Provisions concerning "carbon tariffs" made their way into the climate bill only one day before voting in the House, in a bid to win the support of representatives from the country's manufacturing centers for the whole bill.

Such provisions are welcomed by some senators as well, and the bill is now under discussion in the Senate. Max Baucus, president of the Senate Finance Committee, said in November the Senate's version of the climate bill must also include some forceful "border measures".

To date, taxing carbon emissions has been confined to domestic behavior in most countries as a way to better protect the environment, urge manufacturers and people in the country to cut down on emissions and save energy, and help shape public awareness of environmental protection.

Some experts worry that, once carbon tariffs are implemented, it might be used by countries in foreign trade as a way to shelter local enterprises from foreign competition.

The U.S. stance has been criticized by many, who claim the country which holds historical responsibility for climate change professes it will conserve energy and cut emissions on the one hand, while on the other, tries to pass its domestic problems on to other countries.

Justin Yifu Lin, World Bank vice president and chief economist, said the carbon tariffs proposed by some developed countries would bring more disadvantage to developing countries.

The industrial structure in developed countries had been optimized, with service industries becoming dominant and carbon emissions lowered, Lin said,adding the industries in which developing countries hold a comparative advantage had higher carbon emissions, such as agriculture and manufacturing.

Therefore, the carbon tariffs proposal went against the benefits of developing countries, he said.

Carbon tariffs provisions have received wide criticism both in the U.S. and the international community.

Countries including Germany, Sweden and India have criticized the proposal for breaching the rules of the World Trade Organization and the principle of "common but differentiated responsibilities" stipulated in Kyoto Protocol, saying it would seriously hurt the interests of developing countries.

U.S. Energy Secretary Steven Chu told media in October that the U.S should focus on cutting its own greenhouse gas emissions and developing clean energy technologies before slapping carbon tariffs on imported energy-intensive goods.

The country's Chamber of Commerce and National Foreign Trade Council believe that imposing carbon tariffs would trigger a trade war and harm U.S. exports in the end.

Julian L. Wong, a senior policy analyst at the Center for American Progress, said the carbon tariffs provisions sent the wrong message to the international community.

Wong said the measure reflected the fact that some U.S. legislators only cared about the interests of their own constituencies or states, ignoring the international United States' obligations.