Overfishing is becoming increasingly recognised for the ecological disaster that it is. The capacity of the global aggregate fishing fleet is at least double of what is needed to exploit the oceans sustainably, and fishing methods such as industrial bottom trawling have proved particularly destructive. Add to this the rise in atmospheric carbon dioxide, leading to increased sea temperatures and ocean acidification, oil spills, agricultural and industrial run-off, pollution from aquaculture, and the enormous accumulation of plastic debris in water, and the critical situation for marine wildlife becomes clear.

But less is said and written about the social dimensions of this disaster. This is not simply a case of an industrial sector hurtling down a path to its own economic extinction. There is also a whole way of life at stake for some of the world's most vulnerable communities.

The scrubby desert outside Port Augusta, three hours from Adelaide, is not the kind of countryside you see in Australian tourist brochures. The backdrop to an area of coal-fired power stations, lead smelting and mining, the coastal landscape is spiked with saltbush that can live on a trickle of brackish seawater seeping up through the arid soil. Poisonous king brown snakes, redback spiders, the odd kangaroo and emu are seen occasionally, flies constantly. When the local landowners who graze a few sheep here get a chance to sell some of this crummy real estate they jump at it, even for bottom dollar, because the only real natural resource in these parts is sunshine.

Which makes it all the more remarkable that a group of young brains from Europe, Asia and north America, led by a 33-year-old German former Goldman Sachs banker but inspired by a London theatre lighting engineer of 62, have bought a sizeable lump of this unpromising outback territory and built on it an experimental greenhouse which holds the seemingly realistic promise of solving the world's food problems.

As US cornfields withered in drought conditions last summer, Brazil's once empty Cerrado region produced a bumper crop of the grain, helping feed livestock on US farms and ease a drought-related spike in prices.

US imports of Brazilian corn were small by world standards. But they are rising fast, and they mark just one element of the increasingly complex and sometimes contentious relations between the world's agricultural superpower and its fast-growing competitor amid shifts in the global economy.

Starting at zero in 2010, Brazilian corn exports to the US are on pace to exceed $10m this year and are bound to rise as farmers expand planting and more corn is funnelled to nonfood uses, such as ethanol production. Brazil is expected next year to dethrone the US as the world's largest producer of soybeans. With so much land available for cultivation, that status will probably become permanent.

Canada's multimillion dollar proposal to cull grey seals will not bring back the ravaged stocks of Atlantic cod it is intended to help, scientists have said.

In October, the Canadian Senate approved a controversial plan to kill 70,000 grey seals in the Gulf of St Lawrence under a bounty system next year, ostensibly to revive the cod stocks that the seals were eating.

But a group of marine scientists at Dalhousie University in Halifax, Nova Scotia, have said in a recent open letter: "There is no credible scientific evidence to suggest a cull of grey seals in Atlantic Canada would help depleted fish stocks recover.