"For us it's not something far in the future, it's already happening."

Climate change and rising global food prices are at the top of the G8's agenda this year. Van Schalkwyk called on developed countries to slash emissions by 80 to 95 percent by 2050 compared with 1990, to achieve meaningful progress in fighting climate change.

Developing countries like South Africa, which holds most of the continent's coal reserves and is expanding output, will need technology transfers to slow their growth in emissions, he said.

Otherwise, increasing dryness in the west would be matched by cyclones and heavy rain in the east, fanning the spread of malaria and destroying infrastructure that wasn't built to withstand strong winds and heavy rains.

As its western regions dry out, South Africa would have to turn to more drought-resistant strains of maize, or corn, giving a greater role to genetically modified strains, he said. GMO corn is already legal in South Africa.

South Africa consumes about 8 million tonnes a year of corn. It produced 7.125 million tonnes in the 2007 harvest, but this year's harvest topped 11 million tonnes following better rains.

In December, the country specifically excluded maize from the materials that could be used to make biofuels, despite protests from a grain-growing lobby that fears drops in prices when output is high.

Van Schalkwyk called for an international framework to set policy on biofuels, which by diverting excess grain supply helped push corn futures in Chicago to an all-time high last month.

"We believe that is the responsible approach. We were criticised then, but now we are proven right," he said. (Editing by Hugh Lawson)