It's our duty as Americans to protect our national parks for the next hundred years —Alex Honnold

Rock climber Alex Honnold argues we must do more to defend US national parks from a slew of imminent environmental threats

Just over eight years ago, I completed a free solo ascent - unroped - of the one of the most beautiful and challenging climbs in the world: a 350 metre crack called Moonlight Buttress in southwestern Utah's Zion national park. At the time, Alpinist magazine called it "one of the most impressive free solos ever achieved."

While I find it hard to articulate exactly why I'm drawn to this type of exposed, unroped climbing, the setting certainly plays a big role. Zion is aptly named: it's a promised land of striking multicolored sandstone cliffs soaring from a green valley below. Though I'm intensely focused when I climb, the gift of doing it in such breathtaking places is not lost on me.