US President Barack Obama touted his new climate change proposal in his weekly address Saturday, calling for Americans to lead the charge against the warming environment.

"Those who already feel the effects of a changing climate don't have time to deny it -- they're busy dealing with it," said Obama in his pre-recorded address on radio and the Internet.

"The firefighters who brave longer wildfire seasons. The farmers who see crops wilted one year, and washed away the next. Western families worried about water that's drying up.

"The cost of these events can be measured in lost lives and livelihoods, lost homes and businesses, and hundreds of billions of dollars in emergency services and disaster relief. And Americans across the country are already paying the price of inaction in higher food costs, insurance premiums, and the tab for rebuilding.

"The question is not whether we need to act. The question is whether we will have the courage to act before it's too late," the president said.

Obama laid out a broad new plan to fight climate change on Tuesday, using executive powers to get around deniers who have blocked action in Congress. He called for new restrictions on existing and new power plants to curb carbon emissions, pledged to push new generation clean energy sources and to lead a fresh global effort to stem global warming.

"This is the fight America can and will lead in the 21st century. But it will require all of us, as citizens, to do our part," the president said Saturday, calling for scientists to develop biofuels and farmers to grow them, engineers to design clean technology and businesses to get them to market.

"We will be judged -- as a people, as a society, and as a country -- on where we go from here," Obama said.

Some opponents of his approach have warned that the plan could result in older coal-fired plants being taken offline and may thereby raise electricity prices for consumers, which could disproportionately hurt the poor.

Officials counter that the plan will reduce the amount of electricity used -- thereby reducing fuel bills.

However, the specifics of much of his plan were unclear, and many of Obama's new rules could face court challenges that would delay their implementation.

Meanwhile, speaking for Republicans on another contentious issue, Senator Pat Roberts from Kansas raised concerns over the health care reform package Obama championed in his first term.

The Affordable Care Act, passed in 2010 and upheld by the Supreme Court in 2012, aims to provide health care coverage to an additional 30 million Americans. States are to implement it gradually by 2014.

But many Republicans remain staunchly opposed.

"As we celebrate the 4th (of July Independence Day holiday), it will be a mere 89 days until the October 1st deadline, when millions of Americans are forced to purchase health insurance in a special marketplace ... overseen by the federal government," Roberts said.

"Health care as you know it will change," he warned, suggesting many aspects including cost, coverage, and side effects were still unknown.

Roberts has proposed a law that would repeal the marketplaces, as well as other provisions related to the mandate to buy insurance, if the Obama administration misses its deadline.