Who cares if we all reduce our carbon footprint – if there are billions more of us. It still adds up to a greenhouse gas disaster.

For Dr. John Guillebaud, a UK population expert – controlling our numbers is a biological necessity – and one key factor in averting the worst of climate change.

Since his early days growing up in Africa, this medical doctor has devoted himself to family planning. Now he, and a team at Optimum Population, have calculated just how many air miles, or driving miles, each new member of the human race adds to the atmosphere.

For the average person in Britain, where people use almost half the energy of someone from California, deciding to have one less child reduces greenhouse gas equivalent to 620 flights from London to New York – or over 3 million miles in a Toyota Prius (the most efficient mass produced vehicle we have.)

One less child in an under-developed country still saves a million Prius miles.

Dr. John isn’t any kind of fanatic. He doesn’t want Mao-Tse Tung “one child” type laws. A practical family can have two kids (to replace the parents) – and maybe three if others don’t have any.

Even in places like Africa, which Guillebaud knows intimately, women would like to have far less children – if only they had access to birth control we all take for granted. They don’t get the family planning, the pill, the IUD, or much of anything – making the average family up to 10 kids each. Even with fears of old age, and high child mortality, most African women would love to stop at 5 or 6 at most. But they don’t have that option, when they make love.

Population control is one issue the big green groups, and even the greenest politicians, won’t talk about – for fear of alienating the religious, or being accused of racism. But if we are serious about saving a stable climate – we can’t do it with 9 or 12 billion humans.

And not just the climate. Our numbers have already escalated beyond Earth’s carrying capacity. Eventually, like all other species, our numbers will crash – and not in ways we can control. That won’t be pretty.

For Guillebaud, family planning, women’s choice, and contraception are part of the green toolbox we need to save the planet.

Listen to the full interview by clicking the title above – it’s really worth your time.

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Optimum Population has a briefing paper on their website that explains the links between population and climate change. Since they published their short press release, they have been inundated by requests for media interviews. Radio Ecoshock was lucky to get in there for you, so give it a listen.

Dr. John Guillebuad is Emeritus Professor of Family Planning and Reproductive Health, UCL (University College, London).