The challenge faced by the world during this century, in order to feed a growing world population, is to get more out of farming resources while cutting greenhouse gas emissions from agriculture and reducing other environmental externalities.

With the world's population growing from 7 billion people to 9 billion, our ability to feed all these people becoming an intrinsically scary problem, with climate change making global food insecurity much, much worse.

The recent United Nations climate talks in Durban, heard Oxfam warn that extreme weather threatens food security - from the drought in the Horn of Africa to heat-waves in Russia destroying crops, to heavy monsoonal rains pushing up rice prices in south-east Asia. Indeed, the United Nations Food and Agriculture Organization (FAO) warned that widespread degradation and deepening scarcity of land and water resources have placed many important food production systems at risk with no region being immune.

Sadly, in Australia, many people have grown somewhat used to watching poor people starve overseas - Australia likes to think it will always be able to feed itself. Possibly this may be the case as Australia has a tiny population, is a big food exporter, feeding 60 million people, including ourselves worldwide.

Yet Australia is also the driest inhabited continent and is highly vulnerable to global warming.

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Scientists have warned that unmitigated warming would reduce economic production from irrigation in the Murray-Darling Basin by almost half before 2050. The FAO considers the basin, responsible for 40 per cent of Australia's agricultural output, ''at risk''. The recent release of the draft basin plan met an outcry about the impact on food production of cuts in water availability of 2750 billion liters - a 25 per cent reduction on 2009 extraction levels.

The Australian Bureau of Agricultural and Resource Economics forecast the cuts would reduce the gross value of irrigated agriculture production by 9 per cent this decade, roughly a 4 per cent cut in the basin's total agricultural production (or less, as irrigators revert to dry-land farming).

With regard to global warming, scientists have estimated that 1 to 2 degrees of warming and rainfall changes in the Murray-Darling Basin of plus 5 per cent and minus 20 per cent. This suggests that the Murray River flows could change from an increase of 7 per cent to a decrease of 41 per cent by 2030.

Food security is often framed in the global sense, and because most Australians have access to enough food, they do not think about it as being on our their doorstep. But there are some early signs that it is already happening here.

With some exceptions, worldwide farm productivity gains are starting to taper off. Over the last 50 years, the world has lifted food supply by 180 per cent, while population has increased 120 per cent. But those gains came from increased resource use - more land, more labour, more energy, more water, more fertilizer and pesticide.

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The challenge faced by the world during this century, in order to feed a growing world population, is to get more out of farming resources, while cutting greenhouse gas emissions from agriculture and reducing other environmental externalities.

Ensuring adequate food supplies in the future, despite climate change, will require farmers to be innovative and adaptive. Worldwide, the picture is not clear yet. However imminent, threats to our food supply are much more concrete than the death of the Great Barrier Reef or the loss of Arctic summer sea ice.

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