How to save the world - don't have more than two children

British couples should have no more than two children to save the world from global warming, according to a green think tank.



Campaigners from the Optimum Population Trust said limiting family size was the 'simplest and biggest' contribution people could make to saving the planet.



While Britain need not follow the example of China and ban large families, having more than two children should be frowned upon in the same way as using a patio heater or driving a gas guzzling car.



But critics said doctors and governments had no right to tell parents how many children to have - and that population control could lead to more problems than it solved.

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The controversial call comes from Prof John Guilleband, emeritus professor of family planning at Imperial College London, and GP Dr Pippa Hayes.



The Optimum Population Trust was at the centre of a row in 2003 after suggesting the ideal population for the UK was 30 million - around half its current level.



Writing in the British Medical Journal, they called on family doctors to 'break their silence' on the links between large families and climate change.



'Unplanned pregnancy, especially in teenagers, is a problem for the planet, as well as the individual concerned. But what about planned pregnancies?" they said.



'Should we now explain to UK couples who plan a family that stopping at two children, or at least having one less child than first intended, is the simplest and biggest contribution anyone can make to leaving a habitable planet for our grandchildren?'



A child born in the UK will be responsible for 160 times more greenhouse emissions than a child born in Ethiopia, they said.



'We must not put pressure on people, but by providing information on the population and the environment, and appropriate contraception for everyone, and by their own example, doctors should help to bring family size into the arena of environmental ethics, analogous to avoiding patio heaters and high carbon cars," they added.



In the UK which has the highest rate of teenage pregnancies in western Europe, population is officially projected to rise from 60.6 million to 77 million in 2050 - more than another two Londons. A 'two child' policy would reduce the figure to 55 million, they said.



The researchers warn with world population exceeding 6.7 billion, humans consumption of fossil fuels, fresh water, crops fish and forests is outstripping the planet's biological capacity.



Countries such as Costa Rica, Sri Lanka and Thailand, have reduced their fertility rates by improving access to contraception and through education, they said.



Critics of population control say it fails to tackle the real threats to the environment. And reducing Britain's population could lead to huge social problems if there were not enough young people to pay for the care of the elderly.



Robert Whelan, of the Civitas think tank, said the way to tackle environmental problems was through eradicating poverty - not limiting population.



'These people think that they know how many children people should have. But the only people who should make that decision are parents themselves," he said.



'We have to treat with great suspicion any attempt to interfere with the choices of parents either in the third world or in the first world.' Most mainstream green groups shy away from discussing overpopulation, believing the subject is too controversial.



The Optimum Population Trust's supporters include actress Susan Hampshire and environmentalist Jonathan Porritt.



Its views echo those of Malthus - the 18th century economist who claimed population would rise more quickly than food production triggering mass starvations.



Until it was discredited by Nazism, population control in the first half of the 20th century was most closely associated with eugenics - the belief that 'undesirable' qualities should removed from populations to improve future generations.



The rise of the green movement in the 1970s and 1980s led to a revival in calls for population control.

