Should Aussie parents be taxed for extra kids?

Couples who have more than two children should be charged a lifelong tax to offset their extra offspring's carbon dioxide emissions, a medical expert says.

A new report published in an Australian medical journal has called for parents to be charged $5,000 ($NZ5700) a head for every child after their second, and an annual tax of up to $800 every year thereafter.

And couples who get sterilised would be eligible for carbon credits under the controversial proposal.

Perth specialist Professor Barry Walters is heavily critical of the $4,000 baby bonus, saying that paying new parents extra for every baby fuels more children, more emissions and "greenhouse-unfriendly behaviour".

Instead, it should be replaced with a "baby levy" in the form of a carbon tax in line with the "polluter pays" principle, he wrote in the latest Medical Journal of Australia.

"Every family choosing to have more than a defined number of children should be charged a carbon tax that would fund the planting of enough trees to offset the carbon cost generated by a new human being," said Prof Walters, an obstetrician at King Edward Memorial Hospital in Perth.

Sustainable Population Australia suggested a maximum of two, he said.

By the same reasoning, contraceptives like diaphragms and condoms, as well as sterilisation procedures, should attract carbon credits, the specialist said.

"As doctors, I believe we need to think this way," he wrote in a letter to the journal.

"As Australians I believe we need to be less arrogant.

"As citizens of the world, I believe we deserve no more population concessions than those in India or China."

Professor Garry Egger, director of the NSW Centre for Health Promotion and Research, agreed with the call, saying former treasurer Peter Costello's request for three children per family - "one for mum, one for dad and one for the country" - was too single-minded.

"Population remains crucial to all environmental considerations," wrote Prof Eggers, a leading advocate of the personal carbon trading debate.

"The debate (around population control) needs to be reopened as part of a second ecological revolution."

Family groups have rejected the calls, saying larger families use less energy than smaller ones and therefore should not be penalised.

- AAP