But the sheer number of people on earth is not as important as their inequality and how much they consume, said Jules Pretty, one of the working group of 22 who produced the report. "In material terms it will be necessary for most developed countries to abstain from certain sorts of consumption, such as CO2. You do not need to be consuming so much to have a long and healthy life. We cannot conceive of a world that is going to be as unequal as it is now. We must bring the 1.3 billion people living on less than a $1.25 a day out of absolute poverty. It's critical to slow population growth in those countries which cannot keep up with services."
The report gives the example of Niger in West Africa which has increased life expectancy in the past 30 years but is doubling population every 20 years. "Even assuming its total fertility rate (Tfr) falls to 3.9 by 2050, which may be optimistic, the population will grow from 15.5 to 55.5 million by 2050. A future in which population increase outstrips the production of food and other necessities of life is a real possibility for Niger. It is difficult to see a bright future for the country without sharp reductions in fertility and population growth together with increased investment in health and education," it said.
Most of the global population growth in the next century will come from the 48 least developed countries, of which 32 are in Africa, said Ekliya Zulu, one of the authors and president of the Union for African Population studies. "Taking Africa alone, the population will increase by 2 billion this century. If we fail and fertility levels do not go down to 2.1, (from 4.7 now) the population [there] may reach 5.3 billion. When we slow down population growth we empower women and provide more money for least developed countries to invest in education. The majority of women want fewer children. The demand to reduce fertility is there", he said.
The authors acknowledge that it would take time and massive political commitment to shift consumption patterns in rich countries, but believe that providing contraception would cost comparatively little. "To supply all the world's unmet family planning needs would be $6-7 billon a year. It's not much. It's an extremely good investment, extremely affordable. To not provide family planning is an infringement of human rights", said Sulston.
The authors declined to put a figure on sustainable population, saying it depended on lifestyle choices and consumption. But they warned that without urgent action humanity would be in deep trouble. "The pressure on a finite planet will make us radically change human activity", said Pretty.
"The planet has sufficient resources to sustain 9 billion, but we can only ensure a sustainable future for all if we address grossly unequal levels of consumption. Fairly redistributing the lion's share of the earth's resources consumed by the richest 10% would bring development so that infant mortality rates are reduced, many more people are educated and women are empowered to determine their family size – all of which will bring down birth rates", said an Oxfam spokeswoman.
Intellpuke: You can read this article by Guardian Environment Editor John Vidal in context here: www.guardian.co.uk/environment/2012/apr/26/earth-population-consumption-disasters