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 US 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 US has not joined any multilateral emissions agreement by then.

However, the decision has triggered wide debate on whether the US 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.