When people see Eric Larsen and Ryan Waters dragging tires around Boulder's trails, they often ask, "Is the park service paying you to groom the trails?" Larsen said.

They usually just laugh and keep dragging their tires — they're training.

Larsen and Waters, both of Boulder, are not park service employees. They are preparing to pull two 350-pound sleds full of food and gear on a journey of about 500 miles from Canada to the North Pole.

About that inexact number: Waters said the mileage changes because ice shifts. "You can set up your tent and wake up and have drifted several miles," he said.

The temperatures will hover around minus 50 degrees. They will travel primarily on skis, but also use snowshoes, and in some cases have to swim across holes in the ice. They must carry everything they need with them — no resupplies.

Their goal is to break the world record for this journey by doing it in fewer than 49 days.

The two will depart for the North Pole from Canada's Ellesmere Island on March 1.

Waters, 40, is a guide with Mountain Professionals in Boulder. He has already climbed the Seven Summits, the tallest mountains on every continent, and he has skied across Antarctica, but he thinks that this will be his most challenging expedition yet.

"About 5,000 people have climbed Everest," Waters said. "You can count the number of people who have skied to the North Pole on two hands."

Larsen, 42, is also a guide with Mountain Professionals. He has climbed Mount Everest, too, and he skied to the North Pole in 2010 — his second trip there. On that trip, he had the support of additional supplies along the way. Since his last trip, no one has repeated the trip and successfully skied to the North Pole from the starting point, Ellesmere Island in the Canadian arctic, he said. This is the route Waters and Larsen will return to, to complete the trip without resupply.

Ryan Waters skis toward the sun at Svalbard, Norway.
Ryan Waters skis toward the sun at Svalbard, Norway. (Eric Larsen / Courtesy http://ericlarsenexplore.com/)

Waters and Larsen met in Boulder, and climbed Alaska's Denali together in 2009, but they started talking about this unsupported ski to the North Pole as they were both en route to separate expeditions in Antarctica.

In March of 2013, the two traveled to Svalbard, Norway, to train for the North Pole expedition. Recently, they have been training together every day in Boulder. "We see each other a lot, just training and figuring out logistics," Larsen said.

Part of that training has been ski mountaineering here in Colorado. But Colorado temperatures might not prepare them for the cold they'll encounter at the North Pole.

Waters said that the cold will be more difficult to deal with than in other places because of the higher humidity in the Arctic. "In the morning you wake up, and everything will be covered in ice ... Every time you breathe, or cook, you create frost."

Polar-bear attacks are also a concern. "Hopefully we don't encounter them. But it's something we have to be ready for," Waters said. "Our first line of defense is a flare gun." They will also be carrying a sawed off shotgun for worst-case scenarios.

The ice is another factor.

The team will have to ski over very thin ice, at times as thin as one inch thick. Larsen said salt ice has a plastic, rubbery quality that fresh water ice doesn't have. It will actually bend and flow under skis, making it possible to ski over it. However, it can still break. If it does, they will only have two minutes to get out of the water and get dry before hypothermia sets in.

"You're basically traveling on this really dynamic surface that is always breaking, moving together and moving apart," Larsen said. "I've had situations where a big crack has opened up near our tent overnight. We could fall in while we sleep."

Waters struggled to explain the appeal of the trip.

"There's not a lot of times that are really fun," Waters said. "It's hard to explain why you would go and do this ... It's being in those environments. There's nothing more realistic. You really have to be dialed to pull off a successful trip."

Waters said he has dreamed about polar exploration since he was a kid, and is excited for the opportunity to journey to the North Pole.

What is the appeal of polar exploration?

Ryan Waters pulls a sled in Svalbard, Norway.
Ryan Waters pulls a sled in Svalbard, Norway. (Eric Larsen / Courtesy http://ericlarsenexplore.com/)

"That's a good question," Larsen said. "I'll let you know when I come up with an answer... It is an incredible place to be. The challenge for me lies with connecting people with that place and communicating how incredible it is despite those challenges, and how important it is for a healthy planet."

When the team reaches the North Pole, people they have contracted will meet them and fly them out. It won't be a two-way journey.

Contact Jake Kincaid at jacob.kincaid@colorado.edu.