The UK's Hadley Centre projects that drought could regularly affect 40 per cent of the planet's land area by the end of this century.

Their soil moisture projection suggests that regions once thought to have big farming potential, like Brazil, southern Africa and the Indian grain bowl, may prove unreliable.

The International Food Policy Research Institute has warned of a potential 30% drop in irrigated wheat production in Asia and 15% in rice, due to climate factors. The World Bank fears African productivity could halve and India's drop by as much as 30 per cent, unless urgent steps are taken.

Ecological overshoot is the term used by the Global Footprint Network to describe how humanity now withdraws more resources from the planet than it is able to replace in a year.

The GFN estimates we consume the total productivity of 1.3 Earths in food, water, energy and other resources. If the trend continues, they say, we will be using 2 planets' worth of production by 2050.

If the GFN is even partly correct, then today's diet and agricultural systems are not sustainable in the longer term.

We must reinvent them.

Julian Cribb is an award winning science writer with over 7000 published articles. He is a Fellow of the Australian Academy of Technological Sciences and Engineering (ATSE) and principal of Julian Cribb & Associates, consultants in science communication.

His forthcoming book The Coming Famine is about the global food crisis.