Transcript for Professional ice climber Will Gadd helps scientists learn more about climate change
Fear and danger are constant to me. They remind me to pay attention. The places that I work in are really hazardous. If you're not afraid in that environment, something is wrong with you. Reporter: Where most see a remote and unforgiving landscape, will Gadd sees a play there's no mountain high enough, no water fall dangerous enough for this extreme ice climber. Even the mighty niagara falls proved no match for Gadd. That's him on top of the frozen cascade, the first person ever to make the climb. Gadd is a living legend in the climbing world. Now he's using his influence to sound the alarm about climate change. That was exciting. Reporter: Taking him from the last remaining ice on Africa's highest peak. Some estimates, there won't be any ice on top of kilimanjaro in less than ten years. Reporter: To the depths of the melting arctic. A remarkable journey that all began here in the far, freezing reaches of the Canadian rockies. How long have you been coming to this glacier? I just figured it out. I've been coming here for 45 years that I remember. I remember being a kid in elementary school and driving out with the family, and the glacier being right here. Today it's way back there. Reporter: A warning of the effects of climate change. There should be a glacier here. Reporter: Why should anyone care about a melting glacier? Glaciers are the symptom. When glaciers are retreating this quickly, something is changing very, very quickly in our world. Reporter: The glacier has lost more than half its volume and receded nearly a mile in the past 125 years. Yearly markers let visitors know just how much has vanished over time. Unassuming monuments with profound implications. When I come back here and I see that the glacier's receded more, it's a reminder of how quickly things are changing. It's an obvious marker. You read in the newspaper about climate change. It's abstract. But you come out here and the glacier has moved. Reporter: After years of watching his ice melt away he felt compelled to put his climbing skills to use. Okay, martin. Reporter: By guiding scientists into places once thought inaccessible. Good, martin, doing great. Reporter: With Gadd leading the way in 2016, scientists were able to explore the inside of the glacier for the first time in history, prompting unexpected discoveries. That's biofilm. You look at a glacier, and I would think nothing's living in here. That's what we believed. It's cold, now we know we're completely wrong. Reporter: And there's evidence right there, right? And totally accidently we found new life forms down there. That's a special thing. I'm athlete, but to help our collective knowledge move forward a bit is really satisfying to me. Reporter: The united nations recognized Gadd's impact in 2019 naming him a mountain hero. Having will on our project was critically important for us, because we were going into a cave with some unknowns. Reporter: Jason gully, a glaciologist at the university of south Florida recently enlisted Gadd's help. We got winds around 50 miles per hour, temperatures dropping below zero. And we drop in to what happened to be one of the coolest caves I've ever entered. I've never been in anyplace like this ever. Me either. This is next level for sure. Reporter: Gadd took scientist scientists into a plunging cave, giving them unprecedented access. There's tremendous research going on in Greenland. If the Greenland iets sheet were to melt, it would raise sea levels five to seven meters. Reporter: And that damage can be costly. A study released just this week warns that the melting arctic could cost the global economy nearly $70 trillion. Gadd's team had hoped to study the frigid waters beloet ice sheet, but here science comes with risk. That was exciting. I was afraid. There is so much debris and so much power in there, it was not a safe place to be. And this research is important. But it's not worth dying for. Right there. You guys see this crack here? We've got a bunch of cracks. You know, that are basically in alignment with the block that's overhanging. Really short version, that ice is all messed up. And we are not stoked. What we weren't really prepared for was how unstable the cave was. There'd be these big chunks of ice previously attached to the ceiling that had fallen onto the floor. That's end of it right there. The ceiling comes down, the pool goes into it. We couldn't go any further. Even if we were crazy enough to come here and die, and now I think it's an excellent time to leave. One of the things that we're always concerned about as sign hits is the risk of some of these projects and having somebody like will who's really, really good technically but also spends a lot of time thinking about risk management makes our job that much easier as we're doing science. We understand how the icecap works now as a result of the work that Jason and I did together. I love that. As athletes, we're not known for being super smart, but I'm helping some super smart people get in there. Reporter: To get a better sense about what Gadd needs to teach the scientists, we had him put me to the test. A private training session in an imposing setting. Wow. Yeah, look at this. Reporter: That's where we're going. We're climbing up that. Reporter: First, Gadd showed me how it's done. Scampering up the wall like nothing. As long as you do it the same it's all good. Basically. Reporter: You just have decades of experience. You're going to do great. Reporter: And now. Stand up on it. You don't need to kick right away. Reporter: It's a grueling task. But with some moral support from the man called the best ice climber of his generation. Victory! Well done. Welcome to the Canadian rockies, aye? Reporter: Would I be able to go on an expedition with you to go do science? You've got the basic ice climbing part, there's about four more levels of this. Reporter: But even with the basics, Gadd says there should be a sense of urgency. I am optimistic we can stem the tide in some way, but I think we're going to have a lot of pretty wild change on our planet. And I'm going to teach my kids to expect radical change and embrace it. Short term, we're in it. It's going to be difficult. Long term, I think when people pull together they can do anything. Reporter: Fore"nightline," I'm will reeve. You can watch "Beneath the ice" on the rid bull website. Coming up, three Disney
This transcript has been automatically generated and may not be 100% accurate.