The world must act now to avoid conflict over food, land and water spreading from hot spots such as Syria to power centres like London and New York, according to a top science writer.
Julian Cribb, an award-winning Australian journalist, called for an overhaul of global food production to avoid disputes over resources proliferating in new territories.
"We tend to think of food crises as something that happens in Africa or some other developing country," he told the Thomson Reuters Foundation by phone.
"We think supermarkets will always be full of food… But the world only has about three months’ supply of grain in store at any one time," said Cribb.
The world's food systems are coming under increasing strain from a combination of climate change, water scarcity and soil and biodiversity loss, he said.
Yet if harvests were to fail in a major grain-growing region, prices of grain and bread would spike, he said.
"Supermarkets can be emptied in 24 hours, if people panic. We are far closer to hunger than most of us suspect," said Cribb, whose book Food or War, published by the Cambridge University Press, comes out in October.
Globally, more than one in four people struggles to eat healthy food and one in nine goes hungry, according to the United Nations.
Cribb identified seven "powder kegs" at risk of conflict in the coming four or five decades. South Asia topped the list, followed by Africa and China. United States also made the cut.
South Asia and China are facing critical water shortages that could unleash conflict while fights are already breaking out in parts of Africa over water and grazing rights, he said.
"In America, it is going to take 6,000 years to replace the groundwater they've taken out in the last 150 years," according to Cribb, referring to heavy use by farmers.
"Even though America is an advanced country, with all the technologies and solutions, they've not managed their water well, and they are as vulnerable as many other countries to groundwater shortages."
"I'm not saying a shooting war would break out over water. But there is definitely danger of conflict of various kinds."
He said confrontation could take many forms, from physical to legal, affecting neighbours, governments and industries.
Farming guzzles freshwater, uses fossil fuels and relies on pesticides, he said, urging a new system that is climate-resilient, environmentally-friendly, nourishing and affordable.
Cribb proposed three new options: farming that repairs natural resources, deep-ocean aquaculture that avoids pollution and disease, and the recycling of urban water and nutrients.
There is no time to be lost, Cribb said, as humans devour fertile soil and water at record speed.
"The most destructive object on the planet…is the human jawbone."
- Thomson Reuters Foundation