WASHINGTON (AP) - President Barack Obama says he'll unveil a national plan to combat climate change in a speech Tuesday. Obama says in an online video the White House released Saturday that he'll lay out his vision for reducing carbon pollution, preparing the U.S. for the effects of climate change and leading other nations in the global effort. Obama's speech Tuesday afternoon at Georgetown University will come the day before he leaves for a weeklong trip to three African nations. "There's no single step that can reverse the effects of climate change," Obama says in the video. But when it comes to the world we leave our children, we owe it to them to do what we can. He says scientists must design new fuels and energy sources, and workers must prepare for a clean energy economy. Obama isn't saying what specifics he'll lay out. But White House aides have suggested the steps will include renewable energy and energy-efficient appliances and buildings. The plan is also expected to involve the Environmental Protection Agency using its authority under the Clean Air Act to regulate heat-trapping pollution from coal-fired power plants.