In a rare address to a joint session of Congress marking the fall of the Berlin Wall 20 years ago, Merkel said next month's high-stakes climate summit in Copenhagen hinged on strong US and European commitments.

"I'm convinced, just as we found the strength in the 20th century to bring about the fall of a wall made of concrete and barbed wire, we shall now show that necessary strength to overcome the walls of the 21st century," Merkel said.

Merkel said those were "walls in our minds, walls of short-sighted self-interest, walls between the present and the future."

The German leader reiterated Western nations' stance that any new climate treaty needed commitments from fast-growing emerging economies such as China and India.

"But I'm convinced that once we in Europe and America show ourselves ready to adopt binding agreements, we will also be able to persuade China and India to join in," she said.

"Then in Copenhagen we shall be able to overcome this wall separating the present and future in the interest of our children and grandchildren, and in the interest of sustainable development all over the world," she said.

Merkel's remarks drew a standing ovation from lawmakers from President Barack Obama's Democratic Party, but some Republicans remained seated.

She spoke hours after a key US Senate committee opened a critical debate on climate change with a boycott by most Republicans.

The House of Representatives in June approved the first-ever US plan to mandate curbs on carbon emissions but the bill is facing obstacles in the Senate, decreasing chances of passage before the Copenhagen summit.

Obama supports a so-called cap-and-trade system to mandate curbs in carbon emissions, a sharp change from his predecessor George W. Bush whose stance alienated European leaders.

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