Climbers who come from around the world to tackle North America’s tallest mountain face packing out more of their own human waste after an expert found that a glacier in which much of it is dumped is probably not breaking it down.

National Park Service (NPS) rangers trying to protect the spectacular slopes of Denali – formerly widely known as Mount McKinley – in Alaska are concerned that human poop is blighting the environment there.

Michael Loso, a glacier geologist, calculates that 36,000 mountaineers attempting the treacherous peak between 1951 and 2012 have deposited up to 215,000 pounds of solid human waste on to Kahiltna glacier, on the most popular summit route.

Since 2007, the NPS has required that climbers keep waste off the mountain’s surface. Alpinists catch their poop in biodegradable bags and pitch it into deep crevasses on the glacier.

However, Loso’s research indicates human waste never reaches the bottom of the glacier and will never fully disintegrate. He warns of the prospect of the waste reappearing downstream as stains on the glacial surface, in the otherwise beautiful wilderness landscape.

Officials are now proposing new regulations instructing climbers to drop waste in only one high crevasse, where a huge ice cliff is thought to pulverise the poop and render it inert. Climbers would have to carry out the rest of their waste.

Beyond the aesthetics, climbers on Denali obtain all drinking water by melting snow, which if contaminated by excrement can spread bacterial illnesses, which could be deadly at altitude.

Each year in the short climbing season about 1,100 people with permits attempt Denali’s summit at 20,310ft. More than 90% use a route starting from a landing strip for small aircraft on Kahiltna glacier, flying in from the settlement of Talkeetna, north of Anchorage.

Starting in 2007, the NPS required that human waste be collected in “Clean Mountain Cans”, a portable toilet invented by a Denali park ranger that resembles an extended coffee can.

Loso tested human poop on the mountain and found that after a year, bacteria in the waste had not broken down.