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If a Canadian team gets its way, 10 tonnes of iron dust will be dumped into waters off the coast of Chile. The Oceaneos Marine Research Foundation, a non-profit organisation based in Vancouver, aims to use “ocean seeding” to replenish the sea with nutrients essential for the growth of phytoplankton. The idea is to boost the food chain and revive declining fish stocks.

This has obvious appeal. Globally, fisheries are in dire straits, and if exploitation continues at the same rate, we will run out of seafood by 2048. Chile is a case in point – overfishing has decimated nearly all its major commercial fisheries.

But the proposal has sparked concern among some scientists sceptical of the technique’s benefits and worried about other possible implications. The backlash comes – in part – because of the legacy of a similar scheme in 2012 off the coast of British Columbia, Canada. It caused an outcry and there was no evidence of benefits to the sockeye salmon population it was hoping to revive, or to the Haida community that helped fund the project.

Some critics worry that trials of the sort proposed in Chile could set the scene for something far more elaborate and potentially profitable – using ocean seeding to slow climate change, with the know-how largely in private hands.

The idea that ocean seeding could cool the climate by removing carbon dioxide from the atmosphere isn’t new. It was first proposed in 1988 by a US biochemist named who said: “Give me half a tanker of iron, and I’ll give you an ice age.”

Plankton blooms

Martin’s idea was that restoring nutrients to parts of the ocean lacking them would stimulate plankton blooms, which would suck carbon out of the atmosphere as they grew. Once they died, the plankton would sink to the ocean floor, taking the carbon with them and burying it for centuries.

Since 1990, at least 12 open-ocean experiments have collectively shown that – as a concept – this has merit; one triggered a large bloom, at least half of which sank below 1000 metres to the seabed. But the fear that we will end up nourishing deadly toxic algal blooms or trigger some other unintended outcome led the UN to ban commercial ocean fertilisation in 2008. International law only permits non-commercial small-scale seeding for research purposes.

The proposed trial off Chile fits this bill, so why the outcry? Oceaneos’s Chilean plans are clouded in obscurity, with details of its compounds and methods yet to be spelled out. And in its previous incarnation, the organisation sought to draw down carbon from the atmosphere, a technology it tried to patent.

Given the pace of climate change, it is conceivable that we will have to turn to geoengineering in the future, whether that’s seeding oceans with iron or deflecting the sun’s rays. While neither option is desirable, in choosing the best course of action, research – like the proposed trial off Chile – will be vital.

It’s equally vital that any trials that inform geoengineering – whether intended for this or not – are always conducted for the public good.