Thankfully, the issues of food security and sustainability are back on the international agenda. The big question that confronts us now is this: what does a sustainable food system for nine billion people look like, with changing dietary wants and needs, in a very low-carbon economy?

At the moment, we don’t really have the answers. In the Sixties and Seventies, the answer to the productivity challenge of the time was the ‘Green Revolution’. We now have to deliver the same sort of change in terms of productivity while decreasing greenhouse gas emissions. That is a hell of a challenge because a lot of the gains we achieved in the second half of the last century were associated in some way with putting processed oil into the system, from artificial fertiliser and the transport system through to the way we cook the food at the end.

We can’t afford to do that anymore. For example, this country is committed to reducing greenhouse gas emissions by 80 per cent, and the food chain is going to have to be a major part of that reduction. That problem seems even greater at a global level. We can’t keep clearing forest land for farming. And demand for emissions-intensive foods such as meat and dairy tends to rise with income – accelerating the impact on the climate. We have a pretty good idea what a very low-carbon energy system could look like – but the low-carbon farm?  And will consumers be up for diets that are not low carb so much as low carbon?

There are opportunities, too. It is commonly said that food output needs to double globally by 2050, but we can do quite a lot simply by tackling the level of waste which is embedded in current practices from farms right along the food chain to consumers. There’s a gradual awakening that there’s a huge amount of potential there. By wasting less, we reduce the need for fertilisers, pesticides, fuels and so forth while getting more actual food on plates.  Tristram Stuart’s recent book, Waste, catalogues the problem in agonising detail from end to end.

Here in the UK, government-funded work has resulted in us having good data on what is going on at the consumer end, the amount that we throw away as individuals and households. The Waste and Resources Action Programme (WRAP) has published studies which suggest that the typical British household wastes more than £400 per year in food that is bought and then thrown away. The foxes got to work on some of bins on my road last night; this morning I walked to work along a pavement liberally scattered not only with chicken bones but with fruit, juices, and the like that had been chucked away while apparently still edible – a typical week on a typical street.

Further up the chain, losses that accumulate at the supermarkets don’t necessarily show up in their statistics, but instead appear as waste on suppliers’ accounts through, for example, buyers not anticipating demand properly and the excess getting thrown away. There is over-production and wastage at the manufacturing level. There is also wastage back on the farm, both in terms of crop losses for the old-fashioned reasons of pests and disease or because, for instance, the vegetable crop doesn’t quite meet the quality standards imposed by the buyers. As result, usable food gets ploughed back in.

International data suggest that post-harvest losses in the developing world may be as high as 30-40 per cent. As some of these emerging economies move to distribution systems that look a bit more like those in the West, some of those sorts of losses may disappear. But consumer waste may well rise.

The silver lining in the cloud that was 2008’s food crisis is that people have woken up to the vulnerability of the system and are at least now aware of the issues. More money is now being allocated to international crop research programmes. What really needs to be sustained, and increased, is the work looking at what climate change means for food output and how to respond.

The places that are going to be hit the most by climate change are today’s main centres of hunger in Africa and south Asia. As things stand, it doesn’t take much in the way of disruption of monsoons to have a major impact on proper nutrition in India, for example. Things will be much worse as climate change disrupts existing weather patterns while generally making growing conditions tougher.

Whatever happens in the aftermath of Copenhagen, several decades of change in the climate are embedded in the system already, so we’re going to need a lot of investment in adapting food production to that reality. Part of that response will be varieties of crops that are more drought resistant and systems of water management that are far more efficient than those common today. There is an enormous amount of work to be done.

Andrew Jarvis is a principal at GHK, a policy consultancy, and is a former senior policy adviser in the UK Prime Minister’s Strategy Unit.