Food security will dwarf climate change as the world's most pressing issue in the next few decades, and New Zealand may have seen the first signs of rich or powerful nations trying to secure food supplies for their people.

Actions in recent months by parties linked to Dubai and China appear to support a New Zealand academic's view that food security is a larger issue than has been given credit.

Dubai interests had agreed to fund the purchase of 28 Southland farms through a hapu until the deal collapsed last week, and Chinese interests have reportedly been looking to buy the Crafar family's 22 North Island dairy farms.

China has also made large investments in Africa to secure access to resources.

"Food security is the biggest issue we're facing, and people have not got to grips with it yet," said Jacqueline Rowarth, Massey University's professor of pastoral agriculture.

Little was known about the intentions behind the New Zealand purchases, except Dubai interests planned to sign a 99-year supply agreement for meat, milk and fibre from the Southland farms.

The Crafar farms, however, offered a large, ready resource of dairy products.

Based at Reporoa in the Bay of Plenty, the Crafar family has grown its original property to 22 farms milking 20,000 cows, carrying 10,000 other stock and employing 200 staff.

But it is weighed down by about $200 million of debt and has been placed in receivership.

There are plenty of unanswered questions from the deals, such as how would the products be processed, who were the buyers and would they benefit New Zealand?

Unfortunately, answers have been hard to find as the investors have remained inaccessible to the media.

The failed Dubai venture appears to have tried to sidestep government controls on foreign ownership by funding a New Zealand entity which would technically own the land.

Just who was backing the bid was not determined, but research showed such investments were made by the Dubai Government and not by individuals.

Questions were asked about the deal's authenticity. The New Zealand agents said they did not believe it required Overseas Investment Office approval.

However, the office told the Otago Daily Times that on the information it had, the deal would need its scrutiny.

Agriculture Minister David Carter said it was important not to reject foreign investment outright, but it needed to be controlled.

He said the need for the world to increase food production was at odds with the threat from greenhouse gas emissions, and that was something that scientists would have to address.

Carter acknowledged food security and climate change were two significant global issues.

Rowarth's view that food security was bigger than climate change was supported by a national conference in Australia last year, hosted by Agrifood Skills Australia.

CSIRO Sustainability Agriculture scientist Peter Carberry told the conference that people had started to take for granted the world's ability to meet its food and fibre needs.

But he said demand outstripping supply would dwarf the issue of climate change as the requirement for food and fibre would double within a single lifetime.

The conference said world hunger was viewed as a problem of development, distribution and equity of access - and not the ability of the world's resources to meet global demand. It suggested a rethink of attitude was needed.

"Agriculture research aimed at productivity gains was often seen as a matter of private interest, not global need," Carberry said.

At its How to Feed the World 2050 conference last year, the Food and Agriculture Organisation of the United Nations concluded that demand for cereals would grow from 2.1 billion tonnes today to three billion tonnes by 2050.

However, the advent of biofuel could push demand even higher.

Demand could increase even more sharply for other products, with meat production needing to almost double from about 250 million tonnes to 470 million tonnes.

"The demand for other food products that are more responsive to higher incomes in the developing countries, such as livestock and dairy products, vegetable oils, will grow much faster than that for cereals," said a conference report.

A Royal Society of New Zealand report said pastoral agriculture may have reached its technological limits.

To take the next substantive step to increase production and resist the effects of climate change might require using technology such as genetic modification.

Rowarth said New Zealand could do little to resist growing food demand from population growth pressure from countries such as China, but it was something we might have to get used to.

Foreign ownership could, however, mean changes to the way New Zealand farms were managed or run, providing a challenge for regulators.

In parts of the world housed animals were the norm, while other countries had lower animal welfare and environmental standards which, she said, could influence the way farms were managed.

"If we have external interests coming in, we may have to get use to not quite farming under our expectations."

Based on a measure of calories, New Zealand could feed 18 to 20 million people, but the quality of our products was also an attraction to overseas investors, she said.

The director of Lincoln University's Agribusiness and Economic Research Unit, Caroline Saunders, said New Zealand's attraction was its food surpluses relative to its low consumption.

But she said foreign ownership was not an issue because the land was not going away and it remained in the sovereign ownership of the state.

"In the end the land is still New Zealand land."

Under pressure

* The world's population of 6.6 billion is predicted to reach 8 billion by 2030 and 9 billion by 2050.

* China is already buying up farmland in Africa, and Chinese buyers have been linked to the Crafar farms.

* Dubai interests were keen on buying long-term leases on Southland farms.