Four leading environmental scientists have urged the international community to install a legal trade in rhino horn - in a last ditch effort to save the imperilled animals from extinction.

In an article in the leading international journal Science the scientists argued that a global ban on rhino products has failed, and death rates among the world's remaining black and white rhinos are soaring due to illegal poaching to supply insatiable international demand.

"Current strategies have clearly failed to conserve these magnificent animals and the time has come for a highly regulated legal trade in horn", says lead author Dr Duan Biggs of the ARC Centre of Excellence for Environmental Decisions (CEED) and University of Queensland.

"As committed environmentalists we don't like the idea of a legal trade any more than does the average member of the concerned public. But we can see that we need to do something radically different to conserve Africa's rhino."

The researchers said the Western Black Rhino was declared extinct in 2011. There are only 5000 Black Rhinos and 20,000 White Rhinos left, the vast majority of which are in South Africa and Namibia.

"Poaching in South Africa has, on average, more than doubled each year over the past 5 years. Skyrocketing poaching levels are driven by tremendous growth in the retail price of rhino horn, from around $4,700 per kilogram in 1993 to around $65,000 per kilogram in 2012," they say.

"Rhino horn is now worth more than gold," the scientists note. This growth is mainly attributed to soaring demand by affluent Asian consumers for Chinese medicines.

World trade in rhino horn is banned under the CITES Treaty - and this ban, by restricting supplies of horn, has only succeeded in generating huge rewards for an illegal high-tech poaching industry, equipped with helicopters and stun-darts, which is slaughtering rhinos at alarming rates.

Attempts to educate Chinese medicine consumers to stop using rhino horn have failed to reduce the growth in demand, they said.

The scientists argue that the entire world demand for horn could be met legally by humanely shaving the horns of live rhinos, and from animals which die of natural causes.

Rhinos grow about 0.9kg of horn each year, and the risks to the animal from today's best-practice horn harvesting techniques are minimal. The legal trade in farmed crocodile skins is an example of an industry where legalisation has saved the species from being hunted to extinction.

Furthermore, if rhinos were being 'farmed' legally, more land would be set aside for them and this in turn would help to conserve other endangered savannah animals, as well as generating much-needed income for impoverished rural areas in southern Africa the researchers argue.

They advocate the creation of a Central Selling Organisation to supervise the legitimate harvest and sale of rhino horn globally. Buyers would be attracted to this organisation because its products will be legal, cheaper than horn on the black market, and safer and easier to obtain, they said, adding "horn sold through a Central Selling Organisation could be DNA-fingerprinted and traceable worldwide, enabling buyers, and regulators to differentiate between legal and illicit products."

A legal trade in rhino horn was first proposed 20 years ago, but rejected as 'premature'.

However, the time has now come for a legal trade in horn, says Dr Biggs. "There is a great opportunity to start serious discussions about establishing a legal trade in rhino horn at the 16th CITES Conference of the Parties (COP-16), which is to be held from 3-14 March this year, in Bangkok."

"Legitimizing the market for horn may be morally repugnant to some, but it is probably the only sensible way to prevent extinction of Africa's remaining rhinos," the scientists conclude.

Their paper Legal Trade of Africa's Rhino Horns by Duan Biggs, Franck Courchamp, Rowan Martin and Hugh Possingham, appears in the latest edition of the journal Science (March 1).