Slowly, surely, a new mixture of consensus and fault lines is emerging about world food. On the one hand, there is agreement that we are entering a new era in which basic agricultural commodity prices are rising after decades of dropping. This will hit the poorest hardest, as the new Oxfam report rightly points out. But on the other hand, there is not yet sufficient agreement or political leverage to begin the big changes that are necessary. To make matters more complicated, there's disagreement on what the problem really is.

Is another round of technical intensification needed to raise productivity? That's what the UK's Foresight report argued a few months ago, calling for the oxymoronic "sustainable intensification". Or is it a matter best addressed by more equitable distribution of wealth? This is what Oxfam and others argue, saying there is enough food to go around if properly shared.

To the west, the great success of the food story in the second half of the 20th century was lower prices. This allowed spending to diversify and fuelled the consumer society boom. Proportionately less outlay on food meant more for clothes, homes, holidays and fun. In the world of food, this rebalancing came at a cost to the developing countries dependent on exports. Their purchasing power declined while ours went up. It also came with dire environmental costs: biodiversity loss, pollution, soil damage and water stress. These indicators suggested that the environment, too, was being squeezed.

The warning bells that this 20th-century policy package might be over have been ringing for some time. From the 1960s, with growing evidence and conviction, environmentalists warned that human reliance on the eco-sphere might be threatened. Similarly, public health analysts spotted the transition from problems of under-consumption to those of over- and mal-consumption. Mass hunger sits alongside mass obesity. This bizarre distortion is no longer one where the rich world is fat, and the developing world is thin. Even sub-Saharan Africa now has an obesity problem.

The evidence of this mismatch between policy and reality has been growing for decades. But what can be done about it? That's the question that ought to be centre stage on every national government's food policy agenda. The tragedy is that this isn't the case. For a moment, when in 2006-08 world food prices rose, even powerful countries looked worried. Fresh from the banking crisis, no one wanted food destabilisation too. An emergency world conference was scheduled. But even before it was held, prices began to drop. Sighs of relief in the west. Normality could resume. Three years on, prices are back above 2008 levels, and food inflation is endemic. Oxfam prophesises that food prices will double by 2030. That would take the average British shopping basket to around 20% of disposable income. But to the poorest of the world, it would mean almost all income going on food.

The South African government is reported to be considering whether to emulate Tony Blair's action in 1999 when concerned about food prices. Turn to Wal-Mart. Aware of the vice-like grip Britain's dwindling number of supermarket giants had over 60 million British mouths, Blair sent signals that the UK would welcome the world's biggest food retailer to introduce some price competition. Competition and US capital were to be the recipe to hold down food prices. Wal-Mart purchased Asda, the chain already close to the Wal-Mart giant store model.

Is this model really the answer? Hardly. It's part of the problem. Essentially, the consumer drives to the store. No longer does the food come to the consumer. In a world where oil prices have also rocketed – one of the real reasons for rising food prices – this is no longer an apt model. Surely, the last thing South Africa needs is a retail giant that threatens the existence of thousands of small shopkeepers. Allowing it into Africa may signal modernity, but it's ecological and social irresponsibility.

As Oxfam's report rightly implies, the prospect of food prices doubling ought to be a political wakeup call. But politicians don't seem to be listening yet. They will, I have no doubt.

To be fair to them, the challenge they face cuts across conventional political boundaries. An entire 20th-century approach to food modernity is under threat. Consumer expectations, not least that we can eat whatever we like whenever we like, are at stake.

The 20th century squandered scientific possibilities. It created the fiction that ever more food can be produced by tapping oil, throwing fertiliser at seeds, spraying endless water and treating the soil as blotting paper, a neutral medium. We now know how fragile that mix is, and how fragile the Earth's crust and biology are too. Slowly, some of the institutions created over the last 60 years are recognising that political leadership and redirection are needed. The FAO, WHO, Unicef and Unep all collate the food story. Ministers meet, but in silos. The big picture eludes them. Inaction triumphs.

It's this consensus that Oxfam is confronting. But to do it will require mass support. Politicians have famously short time-horizons.