"We need an agreement on one objective: Global warming must not exceed 2 degrees Celsius," Merkel said, or 3.6 degrees Fahrenheit. "To achieve this, we need the readiness of all countries to accept internationally binding obligations. We cannot afford missing the objectives in climate protection that science tells us have to be met."

Merkel said that people must tear down mental walls that blocked them from seeing the plight of future generations if warming continued unchecked. The world's nations will meet next month in Copenhagen, Denmark, for climate talks. She said they'd need to find the same resolve that Germans had when they brought down the Berlin Wall on Nov. 9, 1989.

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

She urged the U.S. to join Europe in setting a limit on heat-trapping gases from fossil-fuel burning.

"It is true there can be no agreement without China and India," she said. "But I'm convinced that once we -- Europe and America - show ourselves willing to accept binding agreements we will also be able to convince China and India to join." Failure to cut emissions also would result in missed opportunities for sustainable economic growth from clean energy, the German leader said.

Democrats stood and cheered during her comments on climate change, while many Republicans sat without applauding, reflecting the partisan divide on the issue.

"She's going to be disappointed," said Rep. Joe Barton of Texas, the ranking Republican on the House Energy and Commerce Committee. He doesn't accept the view of the vast majority of climate scientists, who say that greenhouse gases from fossil fuels and deforestation are responsible for a rise in global temperatures over recent decades.

Merkel met with President Barack Obama earlier Tuesday at the White House.

"The U.S., Germany and countries around the world, I think, are all beginning to recognize why it is so important that we work in common in order to stem the potential catastrophe that could result if we continue to see global warming continuing unabated," Obama said before the meeting.

Later, after meeting with a delegation of top leaders from the European Union, Obama said they'd discussed climate change extensively and agreed that it's "imperative to redouble the efforts" on the road to Copenhagen to achieve success and avoid "a potential ecological disaster."