This June, the UN hosts the Conference on Sustainable Development in Rio de Janeiro. It’s a return to Rio to stock-take the 1992 UN Conference on Environment and Development.

The 1992 Rio Declaration is portrayed as the point when governments accepted that capitalism needed to include environment and development as central not bolt-on philanthropy. It had taken 20 years of evidence since the UN’s 1972 Stockholm Conference on Environment to get even debating the point.

We need to remember this 40 year history as we approach Rio+20. The Western model of political economy is supposedly lean, quick and efficient, yet faced by the need to become truly sustainable, it’s failing us.

A meeting last week hosted by WWF and the Royal Geographical Society brought together good people from companies, science and policy-making struggling with these limitations.

My own thoughts are that we have institutional failure, not just an evidence-policy gap. The UN is an advisory talking shop. It’s split from bodies such as World Bank and IMF where financial power lies. These splits are replicated at national government level. Our Prime Minister isn’t even going to Rio+20. The environment is ‘off’. Tackling the fiscal deficit dominates Whitehall.

One could be cynical and ask, if in 1992 the world woke up to the problem and on most indicators things still aren’t rosy, why have another Rio jamboree? But what’s the alternative? Drastic action to tackle greenhouse gases won’t come easily. The Greeks are rioting at fiscal strictures. Would the British do likewise if they had to eat differently? Yet we need to. Food accounts for 30% of all greenhouse gases emitted by European and UK consumers.

A wise head at the WWF-RGS meeting said the unthinkable. We need crises to get change. I agree. But we’ve been in crisis since 2008 and all we’ve had are desperate governmental efforts to restore business-as-usual, rather than to re-orient capitalism.

The first documents emerging for Rio+20 fashionably talk of ‘resilience’ but also ‘choice’. Given the choice, people aspire to eat more like the USA. The problem is, it requires five planets to do so. It doesn’t add up.