The world has entered a new food crisis. Prices have surged, contributing to unrest in the Arab world. The president of the World Bank, the former US deputy secretary of state Bob Zoellick, last week warned that global food prices are at "dangerous levels."

It's part two of the crisis that started in 2007-08, which led to food riots in 18 countries. Prices in 2008 reached their highest since 1845, in inflation-adjusted terms, according to the Economist magazine's index, before slumping. The crisis seemed to have solved itself.

But last month, global food prices actually broke the record, according to the experts at the UN's Food and Agriculture Organisation. Over the past year the price of corn has risen 52 per cent, wheat 49 per cent and soybeans 28 per cent.

Rising food prices have pushed an extra 44 million people into poverty in the past seven months, according to the World Bank. It's even being felt in the rich world. In Australia, the opposition hopes to capitalise on it: "The year will begin and end with Australian families facing an ever-rising cost of living," the Liberal Party's Joe Hockey said in a speech last week.

Alarmed at spiking food prices, a score of countries, including big food suppliers such as Russia and Ukraine, have banned food exports to make sure they can feed their own people first.  At the same time, the British government's chief scientific officer, Sir John Beddington, declared that "the case for urgent action in the global food system is now compelling".

There are old and new problems. The most glaring of the old include protectionism in the richest countries. The European Union spends about $365 billion every year subsidising uneconomic farmers and shutting out food exports. The US and Japan are almost as bad. Then there is poverty: 1 billion people who subsist on $1 a day cannot afford to buy food.

There are three new problems. One is the "financialisation" of food. Big investors have come to treat the major traded commodities - including food - as instruments of portfolio investment and speculation. Another new problem is biofuels. Some 40 per cent of the US corn crop, enough to feed 350 million people, goes to make fuel for cars. A third new problem - or perhaps just a recurring one - is extreme weather. If this is just cyclical, it will pass. If it's climate change, it will not.