TODAY'S Daily chart, using data provided by Cargill, is the nearest thing to a snapshot of everything you need to know about feeding the world. It describes whether each region of the world has a food surplus or deficit, and how imports or exports have changed since 1965.

TODAY'S Daily chart, using data provided by Cargill, is the nearest thing to a snapshot of everything you need to know about feeding the world. It describes whether each region of the world has a food surplus or deficit, and how imports or exports have changed since 1965.

Several lessons emerge. First, food trade is significant and growing. Large parts of the world—notably Asia and the Middle East and Africa—cannot feed themselves, so there have to be compensating surplus regions. The biggest are in the Americas. Essentially, the abundant food exports of America's corn belt and Brazil's cerrado go to feed the people of the great cities of Asia and Africa. It is worth bearing this in mind the next time a government proposes to restrict a country's farm exports (as dozens did in 2008 in the wake of soaring prices). Food trade is hedged around by innumerable restrictions which make more inefficient an activity on which hundreds of millions of people depend.

Second, the trends in the main regions show that the biggest agricultural stories of the past few decades happened in Brazil and Russia. The broad regional pattern is as follows: Australia, Central America and Western Europe do not play significant roles. Australia is a fairly large exporter and Europe a biggish importer. But their net trading positions now are similar to what they were in 1980 (Europe moved briefly into surplus in the 1990s but is back where it started). More surprisingly, this is true of the United States and Canada, too. Though America is by far the largest exporting region, its exports have changed only incrementally over the past 30 years. Now look to the import side. Imports have changed a lot. There has been substantial and continuous growth in Asia and the Middle East-Africa-whose imports have risen by about 250m a year in the past 45 years. This growth in demand has been met by a vast expansion of exports from South America, notably Brazil, and a change in the net position of countries of the former Soviet Union, especially Russia and Ukraine; they swung from being the world's second largest importer in 1980 to the world's third largest exporter in 2010. Without the revolution in Brazil's cerrado and the transformation of inefficient collective and state farms after the fall of communism, it is hard to imagine how the cities of Asia and Africa would have been fed. That raises disturbing questions about the future. The dramatic increase in imports in Asia and the Middle East and Africa seems certain to continue. The rise in the past 30 years has been a result of population growth. This will slow a little bit in future as fertility declines in Africa, but only somewhat, partly because population growth in Asia has slowed down already, and partly because the effect of slower demographic growth will be offset up increasing demand for meat. So import demand in Asia and the Middle East will continue to rise. In contrast, it is harder to see where the big changes in supplies will come from. The dramatic surge in South America owns a lot to the spread of farming into the drylands of the cerrado in Brazil, which was previously not cultivated. There is some virgin land left, as well as room for improvements in farm yields. But the miracle of the cerrado was to some extent a one-off event which will not be replicated. That is also true of the collapse of communism: the productivity-boosting transformation of Russian collective and state-owned farms into private property can happen only once.

Hence the last, implicit, message of the chart. If the world is to satisfy the continuing demands of its deficit regions, it needs ideally to find a new Brazil or Russia, a place where the bars can rise steeply on the right hand side. As it happens, there is—potentially—such a place. At the moment, Africa is an importing continent and contributes to the steep slope of the Middle Eastern graph. But unlike most other areas it has ample unused land, adequate water supplies and a lot of sun, the most important ingredients of farming. If the world is to feed the booming cities of Asia and the Middle East, it needs more trade—and a green revolution in Africa.