A food production expert says Australia may face a massive famine if governments fail to address an impending global food shortage.

A conference of food productivity experts in Sydney this week heard the greatest threat to the world is not climate change, but food production on land and in the water.

Science communicator Julian Cribb, an adjunct professor at the University of Technology Sydney, made a keynote address at the seminar saying there is expected to be about 9.2 billion people in the world in 2050, barring wars or major accidents.

But Professor Cribb says that population will create an alarming problem - there simply will not be enough food to go round.

"Basically what the world has not noticed is that hunger has been sneaking up on us for quite a while," he told ABC News Online.

"Population is growing and demand for food is rising.

"Governments have had it so good for so long - the world has had plenty of food - they have become complacent and ignorant.

"Climate change is going to get worse and worse, but the food problems are going to be in the next two to three decades.

"I'm warning now because it takes about a generation to develop new technologies and get them out broadscale. We need to take action now about these things."

Treasury head Ken Henry this week said that Australia's population growth is the biggest challenge to Commonwealth and state governments since Federation.

Professor Cribb agrees it will cause problems, and says governments must not forget future famine goes hand in hand with population growth.

"They have grossly underestimated the potential for population growth in Australia," he said.

"If you get a major collapse in food supply in an area like the north China plains or the Indo-Gangetic plains, there will be hundreds of millions of refugees cut lose so we could easily see 20 or 30 million refugees arrive in Australia over a couple of years.

"That's going to completely alter any plans we might have for a managed population growth.

"This is quite a dangerous situation. We may be OK for food, but if others are not, we will cop the backwash."

He says a range of issues have sparked current food production problems.

"Apart from the obvious things going on in the world food markets, there's a colossal shortage of water emerging because cities worldwide are pinching the farmers' water," he said.

"There's land degradation that's proceeded unabated for about 30 or 40 years now. We're losing land at the rate of 1 per cent of the world's farmland every year.

"We're running into energy shortages, we're running into shortages of fertilisers, and on top of that you've got climate change. All of these things are making the agricultural environment much less certain."

Professor Cribb says governments should be doing a range of things now to fix the problem.

"They need to focus on recycling water and nutrients, putting more science into agriculture to get farmers better technology, stopping cities from stealing farmers' land and water, paying farmers a better price so that they don't destroy the environment that produces the food and opening up free trade in agriculture," he said.

"We really need to get on to this. Australia is as much to blame as any other country for neglecting its agricultural science. Let's face it, this is what keeps the people fed.

"So if you neglect that, you neglect the first and most important thing for any country."