‘Call me Victor,’ says the mustachioed scientist as he picks me up from the airport on a brisk, fall afternoon in Germany. Victor Smetacek is an esteemed marine biologist, but he’s decided to spend his golden years on an ambitious new pursuit. He has devised a plan to alter the mix of gases in Earth’s atmosphere, in order to ward off climate change. He is, in other words, an aspiring geoengineer.

I came to the ancient city of Bremen to ask Smetacek about an extraordinary experiment he performed more than half the world away, in a forbidding sea seldom visited by humans. This sea surrounds the vast, white continent of Antarctica with a chilly current, locking it in a deep freeze. This encircling moat reaches from the surface waters to the ocean bottom, spanning thousands of kilometres. It is known as the Southern Ocean and it is famously dangerous on account of icebergs that hide in the gloom that hovers above its surface. The churn of its swells sometimes serves up freak waves that tower so high they can flip ships over in a single go. It is in this violent, lashing place that Smetacek hopes to transform Earth’s atmosphere.

Since the 1980s, Smetacek has taken regular expeditions from his home port of Bremerhaven to the Southern Ocean aboard the sturdy icebreaker Polarstern. He goes to study the plankton that fill the sea from top to bottom, extending even into the sediments of the sea floor. Plankton is our planet’s most prolific life form, and the food it generates makes up the base layer of the global food chain. The variety of shapes among plankton species shames plants on land, showing more range in size than the difference between moss and redwood trees. There are more plankton cells in the sea than our current count of stars in the entire universe. Indeed, it is precisely this abundance that leads Smetacek to suspect that plankton could be used to change Earth’s environment.

That these tiny creatures could affect such massive change is not as unreasonable as it sounds. Much of the oxygen we breathe comes from just one species of cyanobacteria, Prochlorococcus. This species was not even discovered until the 1980s: it is so tiny that millions can fit into a single drop of water and no one had produced a sieve small enough to catch it. The oxygen made by these tiny marine plants dwarfs that produced by the Amazon rainforest and the rest of the world’s woodlands combined. By taking in CO 2 and exhaling oxygen, these tiny creatures serve as the planet’s lungs, whose steady breathing is limited only by nutrition. Just as land plants need nitrogen, phosphorus and other elements to thrive, missing nutrients restrain planktons’ growth. Add enough of those missing elements – via dust blown off a continent or fertiliser run-off from farm fields – and the oceans will produce blooms that can be seen from space.

Many of these plankton pastures are held back by iron shortages, especially in places that are largely cut off from continental dust and dirt. With access to more iron, the plankton would proliferate and siphon more and more planet-heating CO 2 from the atmosphere. Back in 1988, the late John Martin, then an oceanographer at the Moss Landing Marine Observatory, said: ‘Give me a half tanker of iron, and I will give you an ice age.’

As recently as 2012, the independent would-be geoengineer Russ George attempted to test this theory off the coast of British Columbia, as a follow-up to a fertilising cruise he took in 2002 in a wooden schooner borrowed from the rock legend Neil Young. A bearded, bespectacled little bear of a man who once tried to sell cold-fusion devices, George describes himself as a forest ecologist. But he has spent the past decade trying to commercialise iron fertilisation, most notoriously as part of the now defunct US company Planktos. After that effort was shut down by government and environmentalist outcry, he tried a new tack in the Haida Gwaii archipelago off the coast of British Columbia in 2012. Pitched and funded as an effort to boost salmon runs relied upon by native tribes, George tried to use iron to goose the plankton blooms in the North Pacific, hoping that the gains would trickle up the food chain.

George’s efforts to make money from ocean fertilisation have tainted iron fertilisation, and geoengineering more generally. And that’s a shame, because iron fertilisation could potentially sequester as much as 1 billion metric tons of carbon dioxide annually, and keep it deep in the ocean for centuries. That is slightly more than the CO 2 output of the German economy, and roughly one-eighth of humanity’s entire greenhouse gas output.

In 2004, Smecatek set out to prove the planet-transforming power of plankton with a trio of research cruises to the Southern Ocean. Though we tend to think of ourselves as the only species that can manipulate the environment on a large scale, plankton and their ancestors were the first geoengineers. Some 2.4 billion years ago, photosynthetic bacteria began bubbling out vast quantities of oxygen, becoming the planet’s key source of the gas, a title they have never relinquished. Understanding this fundamental planetary cycle means travelling to the Southern Ocean, where plankton still rule uncontested. But the Southern Ocean is, in the words of Smetacek, ‘one of the least attractive places for human beings on Earth’.

Using an iron sulphate produced as a waste product and sold as a lawn treatment by a titanium production plant back in Germany, Smetacek and his colleagues planned to supply the plankton with the missing nutrient they needed. Fertilising the waters could promote blooms that help sea life thrive all the way up the food chain, even to whale populations, which are still recovering from overhunting. And, more importantly, the uneaten plankton could suck out CO 2 from the air until they die and sink to the sea floor, burying the carbon with them. Smetacek’s ship, the Polarstern, and her six decks, several cranes and 20,000 horsepower-worth of ice-smashing thrust is, of course, made of iron, and her passage sheds tiny traces of the vital nutrient. But it is the iron dumped in her propeller wash that makes the real difference, raising iron concentrations in the surrounding seas by 0.01 grammes per square meter.

The hard part is proving that this audacious plan would work. After all, ocean waters tend to mix, diluting away any iron additions to levels too minute to be measured by human science. Smetacek’s solution was to fertilise a self-contained swirl of water that can maintain its shape for weeks or even months. These eddies form when the fast currents of the Antarctic Circumpolar Current meander into loops that detach and continue to spin until they finally slow and dissipate into the surrounding waters. On 21 January 2004, RV Polarstern steamed her way from Cape Town, with Smetacek aboard as chief scientist, to a rendezvous with the latitudes known as the Roaring Forties and Furious Fifties, where the waves are powerful enough to form the eddies needed for his experiment.

Research vessel R.V. Polarstern anchored in sea-ice. Photo courtesy Alfred Wegener Institute.

On 13 February 2004, Polarstern’s crew finally (and skillfully) brought the ship to the centre of a suitable eddy and dropped a buoy. The scientists had to wear plastic coveralls and gas masks in order to safely mix the irritating iron sulphate powder with local seawater. Using a funnel, they dumped the solution into the Polarstern’s tanks to be stirred, and then slowly circled out from the buoy at the eddy’s centre. Making their way out of the eddy one lap at a time, Smetacek and his team spewed seven metric tons of the ferrous solution in the ship’s propeller wash. As the ship ‘ploughed’ the water it left a rusty red wake, which transformed into a murky green mass that expanded slowly outward through the eddy. By Friday morning, it had covered some 167 square kilometres of sea.

We have the blueprints for a man-made portal for our pollution, a column of plankton running between the atmosphere and the deep ocean

Smetacek and his colleagues settled in for several weeks – dodging the occasional roaring storm – to monitor the fate of their bloom. ‘We have [moved] from the uncertainties of the hunter, full of apprehension as to what the next bend of the front will reveal,’ Smetacek wrote in a progress report, ‘to the fatalistic patience of the farmer, watching the crop develop in the painstakingly selected field.’ As the scientists watched, Chaetoceros atlanticus, Corethron pennatum, Thalassiothrix antarcticus and nine other fantastically named species of diatoms bloomed down to depths of as much as 100 metres over the course of two weeks. By the middle of the third week, the bloom began to die in large enough numbers to overwhelm natural systems of decay. As a result, these drifting corpses fell like snow, to depths of 500 metres. About half of them continued on even further, sinking more than 3,000 metres, to the sea floor itself.

Smetacek’s experiment was a success. For two weeks, he was able to induce carbon to fall to the sea floor at the highest rate ever observed – some 34 times faster than normal. Just as marine and terrestrial plants sucked up CO 2 from Carboniferous or Jurassic skies only to be buried and cooked with geologic heat and pressure into coal, gas and oil, these modern microbes helped pull back some of the CO 2 released when we burned their ancestors to make electricity, or to propel hulks of metal over tarred roads. This marine tinkering could help buffer the ever-increasing concentrations of CO 2 in the atmosphere, concentrations that have touched 400 parts-per-million, levels never before experienced in the hundreds of thousands of years that our clever species, Homo sapiens, has existed. Smetacek has given us the blueprints for a man-made portal for our pollution, a column of plankton running between the atmosphere and the deep ocean.

And yet, environmentalists – the very people who care the most about climate change – were outraged by Smetacek’s project, and tried hard to stop it. A subsequent research cruise in 2009 was held up by international outcry before being permitted to execute a limited follow-up study. Environmental activists stoked fears about unknown side effects. Some worried the iron could lead to a toxic algal bloom, like those that have poisoned sea lions and other sea life off the coast of California. Others floated the possibility that the experiment could lead to a dead zone, like the one created each summer by the algal bloom in the Gulf of Mexico, where the fertilisers that support Midwestern cornfields gush out of the Mississippi river’s mouth and into the ocean. When that algae dies, other microbes consume the corpses, using up all the available oxygen in the surrounding waters. When the oxygen shortages hit, fish flee, but slower-moving sea life such as crabs and worms suffocate and die in droves.

In the wake of Russ George’s rogue geoengineering in 2002, the world’s governments agreed via the United Nations Convention on Biological Diversity in May 2008 that iron fertilisation should be forbidden ‘until there is an adequate scientific basis on which to justify such activities’.

But Smetacek’s research cruise already demonstrated that iron fertilisation works, and the science behind it has been vetted and published in the journal Nature, as recently as 2012. Despite this progress, there have been no scientific research cruises since 2009, and there are none planned for the future. At the very moment it revealed its promise, the white whale of iron fertilisation seems to have slipped under the waves anew.

Back in Bremen, Smetacek told me that commerce might be the only way to motivate further research into iron fertilisation. Replenishing missing krill, and the whales it supports, could be the best route to broader acceptance of the practice. ‘There’s no point in hanging on to things or saying: “It used to be like this.” That’s changed anyway,’ Smetacek said. ‘We’ve changed everything.’

This is the kind of expansive thinking that’s required here at the dawn of the Anthropocene. The ocean is no longer a vast, unknowable wilderness, whose mysterious gods must be placated before it can be crossed. Instead, it’s become the first viable arena for large-scale manipulation of the planetary environment. A land animal has come to tame the heaving, alien world of the sea and, though doing so can make us uncomfortable, in the end it might undo a great deal of the damage we have already done.