Russia’s army is attempting to starve the people of Mariupol into submission in an act of barbarity that almost certainly constitutes a war crime. But the knock-on effects of Vladimir Putin’s invasion of Ukraine threaten hunger, even starvation, for millions of people beyond the immediate theatre of war.

Russia and Ukraine are major food producersaccounting for roughly 30 per cent of global exports of wheat and barley. Russia alone exports 15 per cent of global fertiliser, while Belarus, also under sanctions, is an important producer of potash, crucial for growing soyabeans that in turn go into animal feed . If farmers around the world use less fertiliser, next year’s harvests in Brazil, Argentina and other agricultural powerhouses could collapse.

Ukraine’s wheat exports are being blockaded by Russian ships. Ukrainian farmers don’t have seeds or fuel for their tractors. Grain prices are a third higher than when the war began and two-thirds above where they were a year ago.

For people in the rich world, the coming food shock will put further upward pressure on grocery bills already affected by the highest inflation in decades. For poorer countries, engulfed by the economic consequences of Covid, higher food prices may spell catastrophe.

Millions of people in countries affected by conflict — including Yemen, Ethiopia and South Sudan — are teetering on the brink of famine. Food importers from India to Indonesia face higher bills. Egypt subsidises bread, a staple, for 70mn people, a huge drain on the exchequer. Leaders of other countries in a similar fix will remember the kind of social unrest, including the Arab uprising, that can follow rising food prices.

Given how badly the world has done in distributing vaccines equitably, the omens for how it will deal with a food crisis are not good. The chronically underfunded World Food Programme says rising costs mean it will have to cut rations for millions of people, reallocating food from the merely hungry to the outright starving.

The quickest remedy would, of course, be to end the war in Ukraine. In the longer term, the world should reduce its reliance on Russian food and fertiliser. It should invest more in raising agricultural yields in Africa, which still has plenty of underutilised arable land, and cut down on scandalous food waste in the developed world.

In the short term, there is a clear case for richer countries to increase funding. Sanctions against Russia are entirely justified but richer countries must cushion the blow for poorer ones caught in the crossfire.

One possibility is to look again at the reallocation of Special Drawing Rights, effectively free money, $650bn of which was created within the IMF last year as part of the global pandemic response. Most of it went to rich countries while plans to on-lend a portion to poorer nations have got bogged down.

Individual countries remain free to donate allocations. They should consider doing so. Some mechanism could surely be found to use SDRs more generally to help countries with their balance of payments problems. If that proves impossible, the IMF will need to find emergency resources to help the most vulnerable nations meet their rising food bill.

In the modern era, famines are almost always man-made. Amartya Sen, the Nobel economist, said they could not happen in a democracy because of the free flow of information and the consequent public outrage. But democracy is ever more under attack. Putin is the latest aggressor. Unless he is stopped, hunger will follow.