The World Wildlife Fund says three planets worth of natural resources will be needed by the middle of this century if current consumption rates continue.

The group's Australian CEO, Dermot O'Gorman, told a meeting at Adelaide Town Hall the global population is likely to grow to 9 billion by 2050.

He says the world is already seeing the results of the population having doubled in the past 50 years.

"Everything from increasing water stress and pressures which of course Adelaide and South Australia know very well from the Murray-Darling Basin experiences, through to food shortages globally and the climate problem that we need to face," he said.

He says humans began consuming more resources than were being produced by the 1970s.