Incoming European Union trade chief Karel De Gucht on Tuesday ruled out pursuing French-led calls to impose a carbon tax at the EU's borders, warning that such ideas risk triggering trade wars.

"In terms of border adjustments, I'm against it," De Gucht told lawmakers in response to a question during a European parliamentary confirmation hearing in Brussels.

"I don't see that as the right approach -- it's one that will lead to lots of practical problems.

"We've seen it in the past. The big risk is that it will also lead to an escalating trade war on a global level.

"It is clear that we need to take account in our trade policy of what is happening in terms of preserving our environment and climate.

"But I think we have to take other approaches, (and find) strong policies which are in tune with market laws," he stressed.

Outgoing economic and monetary affairs commissioner Joaquin Almunia also argued against the idea during his own hearing for the post dealing with competition.

"Really, I believe that if we try to find climate-change solutions with protectionist instruments, we will lose in every way," Almunia said during an audition that proved a breeze for the hugely experienced Spaniard.

France and Germany in September called for the United Nations to support a carbon tax on imports from countries that failed to back international efforts to fight global warming.

However, a UN climate change conference held in Copenhagen in December ended with a non-binding agreement that did not address the issue and that Brussels said was a Chinese-US stitch-up that will do little to curtail global warming.

The French government decided last week that a new national carbon tax to fight global warming will go into force in July,

That announcement came a week after the constitutional court struck down a previous version of the measure.