We are in the middle of a demographic earthquake that is reshaping our world. In the past century the human population has increased fourfold. That has caused huge environmental damage, and now global warming.
But I have good news. We are defusing the population bomb. Here is the key statistic that should change how we think about population in the 21st century. Today's women have just half as many children as their mothers. Just 2.5 each, down from five just a generation ago.
That is not just in the rich world. It is the global average today. It is a reproductive revolution going on round the world, right now. It is odd we don't hear more about it.
For 2.5 is getting close to the long-term replacement level. Allowing for girls who don't make it to adulthood, women need to have around 2.3 children to keep up numbers. In half the world, they are now having that number or fewer.
That includes Europe, North America and the Caribbean, China, most of the Far East from Japan to Vietnam and Indonesia, and much of the Middle East and North Africa, from Algeria to Iran.
Yes, even Iran. In the past 25 years, behind the veil, the number of children that Iranian women are having has crashed from eight to less than two. Women in Teheran today have fewer children than their sisters in New York or London.
This reproductive revolution goes against conventional wisdom. Family planning experts used to say that women only have fewer children when they get educated or escape poverty. But tell that to women in Bangladesh.
Bangladesh is one of the world's poorest nations. And still one of the most rural. Its girls are among the least educated, and mostly marry in their mid-teens. Yet they have on average just 2.5 children now.
Neighboring India is also at 2.5: half the figure in 1980. In Brazil, hotbed of Catholicism, most women have two children. The average is 1.8. Nothing the priests say can stop tens of millions of them getting sterilized.
What is going on? I think something very simple. Women are choosing to have smaller families because, for the first time in history, they can.
In the 20th century, the world largely eradicated the diseases that used to kill most children before they grew up. Mothers no longer need to have five or six children to ensure the next generation. Two or three is enough. And that is what they are doing.
There are holdouts, of course -- in parts of rural Africa, for instance, where children are still useful in the fields. But the big story is that in most places, whether they are rich or poor, socialist or capitalist, Muslim or Catholic, secular or devout, with tough government birth control policies or none, most people are now having small families.
It is true that population growth has not ceased yet. We have seven billion people today, and may end up with another two billion or so. I agree that will create problems in some countries. But the world does not face ever-rising human numbers.
Our population nightmares are not coming true. If Africans in the 21st century do what Asians did in the late 20th century, we will soon see peak population.
After that, the world's population could begin shrinking. Because in most of the world, after fertility rates fall from five to four to three to two, they carry on down some way. In Greece in recent years, like in other parts of southern and eastern Europe, women have fewer that 1.5 children.
What does this mean for the planet? Well, peak population is good news, of course. But it won't save us, because rising human numbers are not the main environmental problem any more.
Rising consumption today is a far bigger threat. And most of that extra consumption is still happening in rich countries.
Again, one statistic tells the story. Look at carbon dioxide emissions, the main cause of climate change. The world's richest half billion people - that's about 7 percent of the global population -- are responsible for half the world's CO2 emissions. The poor 50 percent are responsible for just 7 percent of emissions.
So there is no way halting population growth in the poor world is going to have more than a very marginal effect on climate change.
You can do similar calculations for other key environmental threats like water use or deforestation.
Economists predict the world's economy will grow by 400 per cent by 2050. If so, only a tenth of that growth will be due to rising human numbers.
So it is the world's consumption patterns we need to fix. The population bomb is being defused, by the poor women of the world. Hooray. But we in the rich world have not even begun to defuse the consumption bomb.
Every time we talk about too many babies in Africa or India, we are denying this simple fact.
This post is part of a series produced by The Huffington Post in association with TEDxKalamata's conference onJuly 26-27 in Greece. For more information, visit www.TEDxKalamata.com.
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