Obama's remarks in Berlin echoed comments he made in his State of the Union and inaugural speeches this year.
"This is the global threat of our time," Obama said Wednesday. "And for the sake of future generations, our generation must move toward a global compact to confront a changing climate before it is too late. That is our job. That is our task. We have to get to work."
Some environmentalists who cheered those remarks when they were made months ago, criticized them Wednesday.
"President Obama deserves praise for including climate change among the long-term threats facing us all," said Ned Helme, president of the Center for Clear Air Policy, an environmentally friendly think tank. "But he should do more than talk about the problem. The president needs to put the full force of his office behind new regulations that will truly curb greenhouse gas emissions. For too long now, he has produced little action. I'm encouraged that he will finally act and not just ask."
Meanwhile, the environmental community is growing impatient.
"I really can't understand why they haven't moved forward on this more quickly, and we hope that turns around," said Nathan Wilcox of Environment America.
An orchestrated and well-publicized campaign to persuade Obama to reject the Keystone XL oil pipeline, which would carry oil extracted from tar sands in western Canada to refineries along the Texas Gulf Coast, appears to be an uphill battle.
Opponents call the $7 billion project a "carbon bomb" that would carry "dirty oil" and exacerbate global warming. But the State Department in an environmental evaluation concluded that other means of transporting the oil would be worse from a climate perspective.