Delivering a speech at Georgetown University, Obama said that the planet is changing in ways that will impact all of humankind, and that the 12 warmest years in recorded history have all come in the last 15 years.

　　"Americans across the country are already paying the price of inaction," Obama said. "As a president, as a father, and as an American, I'm here to say: We need to act."

　　The president noted that power plants, which currently represent one-third of all U.S. carbon emissions, "can still dump unlimited amounts of carbon pollution into the air for free."

　　"That's not right ... and it needs to stop," he added. "I'm directing the Environmental Protection Agency (EPA) to put an end to the limitless dumping of carbon pollution from our power plants. "

　　Obama described a low carbon clean energy economy as being an engine of growth for decades to come. "There's no contradiction between a sound environment and strong economic growth," said Obama, "Using less dirty energy, transitioning to cleaner sources of energy, wasting less energy ... is where we need to go."

　　Obama said he's directing the Department of the Interior to greenlight enough private renewable energy capacity on public lands to power more than 6 million homes by 2020. He asked the federal government to consume 20 percent of its electricity from renewable sources within the next seven years.

　　He also set a goal to reduce carbon pollution by at least 3 billion metric tons cumulatively by 2030, more than half of the annual carbon pollution from the U.S. energy sector.

　　Some environmental groups praised Obama's new climate plan as a positive signal to the world.

　　"Tackling carbon pollution from power plants is the greatest opportunity and should be at the core of any serious approach to reduce U.S. emissions," Andrew Steer, president of the World Resources Institute, said in a statement. "A comprehensive climate strategy will provide businesses with greater certainty and drive investments and innovation that can charge the U.S. economy. This announcement will have ripple effects that will increase the urgency of action around the globe."

　　Others, however, warned that it's "not enough" to prevent catastrophic warming and extreme weather dangers predicted by scientists.

　　"We're happy to see the president finally addressing climate change but the plain truth is that what he's proposing isn't big enough, and doesn't move fast enough, to match the terrifying magnitude of the climate crisis," said Bill Snape, senior counsel of the Center for Biological Diversity. "This plan is a small step in the right direction but certainly begs for something bigger and bolder."

　　Obama has pledged that the United States would cut emissions by 17 percent by 2020 from the 2005 levels, and according to data released by the country's Environmental Protection Agency in April, emissions fell 6.9 percent from 2005 to 2011.

　　But for most countries, the year of 1990, rather than 2005, is the base year. Compared with that of 1990, U.S. emissions were up about 8 percent, the EPA data showed.