President Obama on Saturday broke from his family vacation in Yosemite National Park to urge Americans to act on climate change, which he argued is destroying the country’s precious natural resources.

“Make no mistake, climate change is no longer a threat, it’s a reality,” the president said in a roughly 10-minute speech, ahead of the upcoming 100th anniversary of the National Parks system.

Obama said Yosemite rangers told him that signs of climate change, or global warming, are already occurring across the roughly 761,000-acre park in California.

“Yosemite’s largest glacier, (once) almost a mile long, is almost gone,” said Obama, standing behind the majestic Yosemite falls.

Global warming has in large part been blamed on human activity and on coal and other fossil fuel-burning plants.

The president has been criticized for vowing, since essentially the start of his presidency, to make developing alternative or green energy a priority, while his administration has proposed changes that have the potential to shutter coal-firing plants and prevent new ones from opening.

He also appeared to take a jab Saturday at presumptive Republican presidential nominee Donald Trump who has threatened to dissolve the Paris climate change agreement.

“This shouldn't lead to careless suggestions about scrapping an international treaty we spent years putting together,” Obama said.

The president attempted to spread to the responsibility to act on all Americans, saying “that’s especially true for our leaders in Washington” and that “our generation” must make an effort.

“Over the last 100 years, there has been plenty to celebrate,” Obama said. “Over the next 100 years, protecting (open) spaces is even more important.”