Antarctic New Zealand's environment manager Neil Gilbert said more robust monitoring is needed to track impacts of tourism.
"The Antarctic Peninsula ... is one of if not the most rapidly warming part of the globe," Gilbert said. "We really don't know what additional impact that those tourism numbers ... are having on what is already a very significantly changing environment."
There are fears that habitat will be trampled, that tourists will introduce exotic species or microbes or will transfer native flora and fauna to parts of the continent where they never before existed.
A major fear is that a large cruise ship carrying thousands of passengers will run into trouble in these ice-clogged, storm-prone and poorly charted waters, creating an environmentally disastrous oil spill and a humanitarian crisis for the sparsely resourced Antarctic research stations and distant nations to respond to.
To reduce the risk of spills, the United Nations' shipping agency, the International Maritime Organization, barred the use of heavy fuel oil below 60 degrees latitude south in 2011.
That was a blow to operators of large cruise ships. Steve Wellmeier, administrative director of the tour operators group, said the ban initially slashed cruise passenger numbers by two-thirds.
But it was only a temporary obstacle to industry growth; large ocean liners can comply with the ban by using lighter distillate fuels in Antarctic waters. About 9,900 passengers are believed to have visited Antarctica on large cruise ships is the season now ending, double the total from 2011-12.
The fuel-oil ban is a rare thing for Antarctic tourism: a binding rule.
The 28 countries that comprise the Antarctic Treaty Consultative Committee have made 27 non-binding recommendations on tourism since 1966, but just two mandatory rules — and neither of those are yet in force.
A 2004 agreement requiring tourism operators to be insured to cover possible rescue operations or medical evacuations has been ratified by only 11 of the 28 countries. A 2009 agreement barring ships carrying more than 500 passengers from landing tourists — a measure to protect trampled sites — has the legal backing of just two countries, Japan and Uruguay.
The United States, by far the biggest source of tourists and tourism operators, has not signed either measure.
The International Maritime Organization intends to enforce a Polar Code, detailing safety standards for ships entering both the Arctic and Antarctic regions. It was supposed to be force by 2013, but the IMO now says it won't be adopted before 2014, and after that it will take another 18 months for the code to be implemented.
Hemmings said the current lack of standards is a problem because increasing numbers of cruise ships are negotiating the poorly charted and storm-prone seas without ice-strengthened hulls as Antarctic legs are added to South American, South Pacific and around-the-world cruises.
Those ships "are not necessarily ice-strengthened, or if they are ice-strengthened, are not ice-strengthened to a high standard because at other times of the year they're doing something different," Hemmings said.
Wellmeier, the industry group official, said the impending rules could knock some currently operating vessels out of Antarctica. In any case, he said he doesn't think tourism there will return to the explosive growth rates of the years before the financial crisis, simply because the ships needed for such expansion are not available.
Tourists far outnumber the scientists and support staff at national scientific research stations in Antarctica during the peak summer season, though the researchers make more of an impact because they stay longer. The summer population at the 39 stations across the continent peaked at about 4,400 in the 2011-12 year.
Wellmeier believes tourists should not be considered separately from the question of overall human impact on the Antarctic environment. He said too often it is research-station personnel who flout the rules.
"We hear horror stories every season," he said. "A group will come ashore from a national program and they're on their day off ... and they're breaking the rules, right and left, smoking and getting too close to the animals."
The United States has been criticized on environmental grounds for building a 1,600-kilometer (995-mile) ice road from McMurdo Station to the South Pole on which tractors drag fuel and supplies on sleds. The road provides a more reliable alternative to frequently grounded air services.
Australia-based adventurer Tim Jarvis sees Antarctic tourists not as a problem, but as part of the solution for a frozen continent where the ice is rapidly retreating. If more tourists see its wonders and the impacts of climate change, particularly on the Antarctic Peninsula, Jarvis said, the world will become more inclined to protect the continent.
"It's a pity we live in a world that's a little bit overregulated in many respects," he said of the prospect of greater controls on tourism.
Jarvis led a party of six in January and February on a 19-day reenactment of British explorer Ernest Shackleton's desperate sea and land journey to a South Georgia Island whaling station in the southern Atlantic Ocean in 1916. After his ship was crushed by sea ice, Shackleton left 22 of his crew at on a remote island, then set sail in a lifeboat on an 800-nautical-mile (1,480-kilometer) voyage to get help.
Jarvis's party encountered 8-meter (26-foot) waves, then repeatedly fell through crevasses as they trekked across the snow-covered mountains of South Georgia. Jarvis suffered frostbite to one of his feet but completed the journey. Three members of his party couldn't complete the climb because of trench foot, a condition caused by prolonged exposure to cold and wet conditions.
While the journey seems death-defying, it was the product of tremendous planning. Jarvis and his party spent more than a year applying for five permits from various treaty countries accompanied by detailed risk assessments and environmental impact statements. They paid for their own backup boat to rescue them in case anything went wrong.
"My broader message to people is that we all have the potential to do far more in our lives than we feel we're capable of doing and we should go and explore that ... but do it responsibly," Jarvis said.