By Marie Rumsby of the Royal Society’s In Verba blog.

In the years that followed the Iranian revolution, when Ayatollah Khomeini returned from exile to Tehran and the country went to war against Iraq, the women of Iran were called upon to provide the next generation of soldiers. Following the war the country’s fertility rate fell from an average of over seven children per woman to around 1.7 children per woman – one of the fastest falls in fertility rates recorded over the last 25 years.

Iran is an interesting example but every country has its own story to tell when it comes to population levels and rates of change. The global population is rising and is set to hit 9 billion by 2050. And whilst fertility rates in Ethiopia are on the decline, its total population is projected to double from around 80 million today, to 160 million in 2050.

Earlier this month, the Royal Society announced it is undertaking a new study which will look at the role of global population in sustainable development. “People and the Planet” will investigate how population variables – such as fertility, mortality, ageing, urbanization, and migration – will be affected by economies, environments, societies, and cultures, over the next 40 years and beyond.

The group informing the study is chaired by Nobel Laureate Sir John Sulston FRS, and includes experts from a range of disciplines, from all over the world. With names on the group such as Professor Demissie Habte (President of the Ethiopian Academy of Sciences), Professor Alastair Fitter FRS (Professor Environmental Sciences, University of York) and Professor John Cleland FBA (Professor of Medical Demography, London School of Hygiene and Tropical Medicine), there’s bound to be some lively discussions.

Linked to the announcement of the study, the Society held a PolicyLab with Fred Pearce, environmental journalist, and Jonathon Porritt, co-founder of Forum for the Future, to discuss the significance of population in sustainable development.

Both speakers have been campaigning against over-consumption for many years. Jonathon Porritt has been a keen advocate for fully funded, fully engaged voluntary family planning in every country in the world that wants it.

“In my opinion, that would allow us to stabilize global population at closer to 8 billion, rather than 9 billion. And if we did it seriously for forty years, that is an achievable goal.” Porritt thinks that stabilizing global population at 8 billion rather than 9 billion would save a large number of women’s lives, and suggests “you cannot ignore the gap between 8 billion and 9 billion if you are thinking seriously about climate change.”

Fred Pearce acknowledges that population matters, but stresses that it is consumption (and how we produce what we produce) that we need to focus on. He feels it is too convenient for us to focus on population.

According to Fred, the global average is now 2.6 children per woman – that’s getting close to the global replacement level of 2.3 children per woman.

“It is no longer human numbers that are the main threat……It’s the world’s consumption patterns that we need to fix, not its reproductive habits,” said Pearce.

The Society will be taking a long look at some of these issues, assessing the latest scientific evidence and uncertainty around population levels and rates of change. The “People and the Planet” study is due for publication in early 2012, ahead of the Rio+20 UN Earth Summit. The Society is currently seeking evidence to inform this study from a wide-range of stakeholders.

The deadline for submissions is October 1, 2010. For more information on submissions, please see the Royal Society’s full call for evidence announcement.

Image Credit: “In Verba” courtesy of the Royal Society.