Retired South African Archbishop Desmond Tutu coined a new moniker for the oil sands Saturday – calling it "filth" in a keynote speech and saying northern Alberta's bitumen production is the upshot of "negligence and greed."

Archbishop Tutu, 82, has called for apartheid-like boycotts and divestment against fossil fuel companies, and in his speech at a First Nations conference Saturday he said "climate change is the moral struggle that will define this century." Following a helicopter tour in the skies above the oil sands region north of Fort McMurray, he said he was "shocked" to see oil in the Athabasca River and he remains concerned about environmental effects of Alberta's oil sands mega-projects.

But ever the peacemaker, his aerial tour appeared to soften the tone of the Nobel laureate and human rights activist.

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"No one wants to see an end to industry. If you have industry that is responsible, they have to be commended and encouraged," he told reporters moments after stepping off the helicopter. "It's not as if we go around saying, 'to hell with them, whatever. Clobber them.'"

He said he learned at least some of the bitumen naturally seeps into the water from the sand, and was impressed what he heard from a senior executive from oil sands producer Suncor Energy Inc. – which paid for the helicopter flight – about the oil sands company's investments in First Nations communities and renewable energy sources such as wind.

Archbishop Tutu was the main attraction this weekend at a Fort McMurray conference focused on treaty rights and the environment, and spoke to a room of about 200, including First Nations members from across the Prairies and Northwest Territories – many of whom spoke about their struggles their loss of traditional territory and concerns about safe drinking water due to energy projects. Archbishop Tutu said he was touched by their stories. Besides hurting the health of First Nation communities, he said projects such as the oil sands are worsening climate change.

"The fact that this filth is being created now, when the link between carbon emissions and global warming is so obvious, reflects negligence and greed," Archbishop Tutu said.

Although producers say they have made strides to make the oil sands less environmentally damaging, oil sands take more energy to produce than conventional oil, and bitumen mines – one method of extraction – use up vast tracts of land.

The man who won the Nobel Peace Prize in 1984 for his work in the battle against South African apartheid said bitumen production is emblematic of a high carbon era that must end. Archbishop Tutu joins a list of critics who have variously described the oil sands as "dirty" or the most destructive industrial project on earth. Earlier this year, rocker Neil Young said the region north of Fort McMurray resembles atomic-bomb devastated Hiroshima. In recent months, Archbishop Tutu has said he stands in solidarity with communities that oppose oil sands pipelines such as Keystone XL, Northern Gateway and Energy East.

The renowned human right crusader was in Fort McMurray to attend the As Long As the Rivers Flow conference, sponsored by Toronto law firm Olthuis Kleer Townshend LLP and the Athabasca Chipewyan.

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Chief Allan Adam of the Athabasca Chipewyan also spoke Saturday, saying multinational companies want to come into the band's traditional territory and develop the resources at a rapid rate beyond the control of his 1,100-person community.

At the same time, the conference is being held at the modern, energy efficient headquarters for the band's ACDEN group of companies, which according to the chief earns more than $250 million in annual revenues from industrial contracts with oil sands producers. While Chief Adam has called for strict environmental regulations and a halt to new projects, he said "we don't want to stop development, we don't want to shut it down."

Mark Little, Suncor executive vice president for upstream operations, travelled with Archbishop Tutu on his helicopter flight. Mr. Little said they found "a lot of common ground."

Mr. Little spent part of the flight talking to Archbishop Tutu about Suncor's investments in community projects, such as First Nations seniors homes, or First Nation business startups.

The Canadian pipeline company behind the proposed Keystone XL project, which would transport oil sands bitumen to the U.S. Gulf Coast, also issued a news release Saturday in rebuttal to Archbishop Tutu's comments. TransCanada Corp. spokesman Davis Sheremata said Archbishop Tutu is entitled to his opinion but sources of energy, such as oil, have a positive impact on the daily lives of people around the world.

"Oil powered the jet that flew Mr. Tutu to Canada from Africa, produced the fuel for the helicopter tour he had planned of the oil sands, and helped manufacture the microphones and TV cameras for his press conference," the release said. "Without oil we wouldn't have fertilizers to grow our food, plastics for surgical tape and heart valves, and gasoline to start the more than 250 million cars in North America every morning."