President Barack Obama speaking in Yosemite National Park, California
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President Obama in Yosemite: 'Climate change is a reality'

This year marks the 100th anniversary of America's National Parks - sites across the US where nature is protected and preserved.

While visiting Yosemite National Park in California with his family, President Barack Obama drew attention to the dangers of climate change.

The BBC's Tim Allman reports.

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