YOSEMITE VALLEY NATIONAL PARK, Calif. — President Obama pressed lawmakers to do more to prevent climate change as he made a pitch for the 100th-year anniversary of the national park system Saturday.

Speaking in front of the dramatic vision of the 2,400-foot Yosemite Falls, Obama cited his presidential forebears, Abraham Lincoln and Theodore Roosevelt, for preserving Yosemite and creating the National Park Service, respectively.

"It is a true expression of our democracy," Obama said in his brief remarks in front of a small crowd and reporters. Obama touted his administration's record of preservation, saying he has protected 265 million acres of federal land and waters, more than any other president.

But he warned that more work remains to help fend off the effects of climate change.

"When we look at the next century, the next 100 years, the task of protecting sacred space is even more important," Obama said. "The most important challenge we face is climate change. Make no mistake: Climate change is no longer a threat — it’s a reality."

Critics have said Obama has used his powers to improperly seize lands, preventing ranchers and others from accessing it.

Obama cited a record number of tourists to national parks last year — 305 million, according to the National Park Service — and said the park have helped spur economic activity in nearby communities and industries such as footwear, bicycles and camping gear.

The president and first lady Michelle Obama surprised a group of fourth-grade students before his remarks to tout the administration's Every Kid in a Park initiative. He also filmed a virtual-reality video with National Geographic.

Recalling the first time he saw a moose, while touring Yellowstone National Park as an 11-year-old, Obama said visiting a park "changes you. You're not the same after that. We've got to make sure every kid feels that way."