Society is failing to address the key challenge it faces over the next 40 years – whether the world can actually sustain a population of nine billion.

Aubrey Manning’s keynote speech at the Oxford Farming Conference on Wednesday, 5 January, asked whether the forecast population was realistic, manageable or sustainable.

“Whatever your cause, it is a lost cause unless you limit population.”

The predicted rise in population is not only realistic, it is inevitable. “There are so many people [in less developed countries] under the age of 25 that haven’t begun to have children yet,” he pointed out.

You can manage it in the short term, but certainly not in the long term, he said. Options include raising production on existing land, bringing new land into production, GM, improving infrastructure and changing diets.

Previous efforts to raise production in less developed countries had led to environmental disasters, he pointed out. “GM crops will put even greater concentration on a few crop varieties and continue our arms race with pests,” he warned.

Nor is it sustainable, said Prof Manning. “I feel we are destroying much of the beauty of the world as well as its life support systems.”

The “inconvenient truth” is that society must address the thorny issue of reducing population growth.

“We seem to have no problem talking about how we provide food for hungry mouths. But the question of preventing the birth of hungry people presents all sorts of problems.”

Prof Manning’s keynote speech preceded the OFC debate “This House believes unrestrained population growth and food security are incompatible”.