Geoff York This image shows a de-horned white rhino and its calf. A new paper argues that humanely harvesting rhino horn could save the animals from extinction.

Surging demand for rhino horn to decorate daggers and treat everything from hangovers to cancer is driving the iconic animals to the brink of extinction. The only way to save them is to humanely harvest rhino horn and sell it legally, scientists argue in a controversial new paper.

Only 5,000 black rhinos and 20,000 white rhinos remain, mostly in South Africa and Namibia, the scientists note. The western black rhino was declared extinct in 2011.

The paper, published Thursday in the journal Science, is a bid to spark "serious discussions around establishing a legal trade" at an international conference on the trade in endangered species that starts Sunday in Bangkok, lead author Duan Biggs told NBC News.

Edna Molewa, South Africa's water and environment affairs minister, told reporters Thursday that the government would consider "extraordinary measures" to save the rhino from poaching, including a legal trade.

"We have been given a mandate by Cabinet not to close our ears to potential and possible trading in rhino horn," she said, and at this year’s conference, South Africa "would listen and gather as much information as possible" on what should be done about trading, Business Day reported.

Humane trade

Trade in rhino horn was banned under the Convention on the Trade of Endangered Species (CITES) in 1977. Since then, demand for the horn has been met by poachers, who typically kill the rhinos before hacking off their horns.

Just days after Rock Center aired Harry Smith's report, "The Last Stand," on the growing epidemic of illegal rhino poaching in South Africa, three of the rhinos featured in the report were attacked by poachers. Rock Center's Harry Smith reports.

"The trade ban restricts supply and that pushes up the price of horn, which increases incentives for poaching and has caused skyrocketing poaching levels," said Biggs, who is a researcher at the Australian Research Council Center of Excellence for Environmental Reporting.

Today’s street value of rhino horn is about $65,000 per kilogram (2.2 pounds), making it worth more by weight than gold, diamonds, or cocaine, according to the paper. As a result of the high prices, the number of rhinos poached has more than doubled each year over the past five years.

Biggs and colleagues argue that the demand for horn can be met by legally shaving horn from a herd of about 5,000 live animals kept on private conservation lands in South Africa. This would lower prices, lure buyers of horn to the legal market, reduce incentives to poachers and thus reduce poaching.

Rhino horn is largely composed of keratin, a protein also found in fingernails and hair. It regrows when cut at a rate of about 0.9 kilograms a year. For about $20, a rhino can be sedated long enough for its horn to be harvested, Biggs and colleagues note.

"It is a product that can be delivered to the market sustainably and humanely and in a way that has broader conservation benefits," Biggs said. For example, sale of the horn could be used to strengthen anti-poaching efforts.

Poachers 'very nasty people'

Sam Wasser is a conservation biologist at the University of Washington in Seattle who has led global efforts to end the illegal ivory trade, which is run by sophisticated crime syndicates motivated by the huge profits in the wildlife trade.

In South Africa, home to three quarters of the last remaining rhinos on the planet, a spike in rhino poaching is threatening the white rhino's survival. NBC News' Harry Smith reports for "Rock Center."

He said the rhino poachers are the same people who poach elephants, describing them to NBC News as "very nasty people that really want to make a lot of money." The paper calling for a legal trade in rhino horn, he said, "grossly underestimates the impact of organized crime on this trade."

In South Africa alone, 668 rhino were killed in 2012; 448 were killed there in 2011. The sharp rise is largely attributed to a rumor that the horn is a cure for cancer. Studies show that it is not. "That's essentially a marketing ploy by organized crime to increase the value and demand for horn," Wasser said.

In order for a legal trade to be effective, he noted, it would need to lower the price of horn from $65,000 to a few hundred dollars per kilogram. "Poachers are going to be trying as hard as they can to get the last rhinos to capitalize on that high price before the price drops, if it ever does," Wasser said.

He added that poaching of elephants increases in the months prior to CITES meetings whenever countries propose a legal sale of ivory because the poachers scramble to benefit from higher prices. He expects the same to happen with a legal rhino horn trade.

If so, the only surviving rhinos will be those under tight security on private lands in South Africa. "They won’t be natural rhinos," Wasser said.

The more effective approach to saving rhinos, he argued, is to focus efforts on breaking apart the crime syndicates that control the ivory trade. "If you do that, you also get the rhino poaching under control because it is the same organized crime groups that are doing this," he said.

This could be easier than it sounds, Wasser added. He works with Interpol, the international criminal police organization, to genetically track the origin of seized ivory. They’ve found most of it comes from a few hotspots. Focusing law enforcement on those hotspots, he said, could shut down the illegal trade.

No silver bullet

Cathy Dean, executive director of Save the Rhino International, a London-based non-profit group, told NBC News that "there is no one silver bullet that is going to solve the rhino-poaching crisis."

Those pushing for legal trade agree that anti-poaching efforts will need to be maintained and policies must be in place to ensure that local communities in and around rhino areas benefit from the sale of horn, for example.

"Broadly speaking, we are in favor of sustainable use and of reducing reliance on donor funding, so the option of legalizing the trade in rhino horn is of interest," Dean said. "But, there are many, many preconditions that must be met before we could support such a measure."

Duan Biggs A white rhino is shown here in South Africa's Kruger National Park. Rhino horn sells on the black market for $65,000 per kilogram. That's more valuable than cocaine.

For example, she noted, South Africa must find a trading partner for the horn. So far the governments of China and Vietnam, where most of the illegally harvested horn is sold, have shown no willingness to participate in a legal trade.

WWF, the conservation organization, said in a statement that private landowners in South Africa are to be applauded for their efforts in rhino conservation, and that "it is vitally important to keep incentives in place" to ensure their continued involvement.

"At the same time, there are legitimate concerns that establishing a legal avenue of horn trade under current circumstances could produce a range of unintended consequences that would undermine the conservation efforts of WWF and its partners."

For example, a legal horn market could serve as a conduit for laundering illegal rhino horn, increase consumer demand and undermine existing law enforcement.

"The situation is not stable enough to entertain any consideration of legal trade in rhino horn," the WWF said.

Biggs acknowledged that the proposal for a legal trade is controversial, but said it is worth trying. "What we know is that the current situation is certainly not working," he said. "It is failing to conserve rhinos and it comes at taking away resources from other conservation efforts."

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John Roach is a contributing writer for NBC News. To learn more about him, check out his website.