PARIS, Jan. 31 — President Jacques Chirac has demanded that the United States sign both the Kyoto climate protocol and a future agreement that will take effect when the Kyoto accord runs out in 2012.

He said that he welcomed last week’s State of the Union address in which President Bush described climate change as a “serious challenge” and acknowledged that a growing number of American politicians now favor emissions cuts.

But he warned that if the United States did not sign the agreements, a carbon tax across Europe on imports from nations that have not signed the Kyoto treaty could be imposed to try to force compliance. The European Union is the largest export market for American goods.

“A carbon tax is inevitable,” Mr. Chirac said. “If it is European, and I believe it will be European, then it will all the same have a certain influence because it means that all the countries that do not accept the minimum obligations will be obliged to pay.”