In two weeks, world governments will meet in Rio de Janeiro to discuss sustainable development, the juxtaposition of people, economy and planet. It’s another big chance to take the temperature of world policy thinking and leadership. It’s likely to be sobering. Politicians just don’t seem to be engaged.

The world’s economies continue to be shaky in the aftermath of the 2008 oil/commodity crisis. Eurozone troubles don’t help. But the real debate is whether the macro-economy is shaky or flaky.

Subscribers to the shaky thesis - most politicians - want things to get back to business as usual. Others believe we’ve had a wake-up call about the unsustainability of what we thought of as normal growth. A sizeable portion of business opinion now accepts we are moving into a new era and that the old growth model is inadequate.

I was hopeful Rio+20 could be an opportunity for clear voices about implications and opportunities. As the tectonic plates of capitalism grind, crises can allow fresh and radical analyses to emerge, but too few have so far.

We need calm, cool heads to work through the enormous challenges that food, health and environment pose. If political leaders continue to bury their heads in the sand, we’ll all suffer.

With colleagues, I’ve been part of a worldwide team of scientists preparing a report on food security for the UN to launch at Rio.

Many recent reports offer similar analyses and options. The collective picture is sobering. Profligate waste in rich countries at or after consumption and in poor countries nearer the farm. Over-consumption creating obesity alongside hunger. Unequal distribution with deep and damaging environmental footprints.

There are options for action beyond the current mantra of producing more food. That’s too simplistic, which is why academics are emulating what predecessors did in the 1930s to 1950s. They are speaking out that progress is possible, but it won’t be the same as what we aspire to now. Supply chains and consumers need to live within environmental limits. They’re not.

We need sustainable diets fed by sustainable food systems. That requires cultural change more than technical fixes.