Two young climate change activists are making a 17,000-mile trek from the North Pole to the South Pole to highlight how the world is changing through global warming. So far, they’ve cycled, skied, sailed and walked. On Friday, James Hooper and Rob Gauntlett crossed the U.S.-Mexico border on bicycles. The expedition took off at the Geomagnetic North Pole on April 8. This is 19-year-old James Hooper.

James Hooper: “We’ve had some amazing reactions. I mean, the whole point of the trip is to try and involve as many people as possible, to try and encourage people to understand about global warming. In the Arctic, the sea ice has thinned by 50 percent in the last 20 years, and in area, it’s actually shrunk by about 30 to 40 percent in the last 10 years. So, I mean, there’s massive changes going on, and we want to make people aware of those.”