Another Life: Are the risks of geoengineering worth bearing?

Michael Viney: Scientists fear key attitudes may change if climate change worsens

As the climate crisis stirs deeper global anxiety, the risks and costs of some forms of geoengineering may come to seem worth bearing.

Geoengineering looks at ways of using the planet’s natural workings to soak up more CO2 from the atmosphere or shield the planet from the rays of the sun. Making more clouds has been one path of experiment. Fertilising the ocean to grow more CO2-hungry plankton is another that grows in scientific refinement and controversy.

Phytoplankton, the basic, microscopic plant life of the ocean’s food chain, needs sunlight and nourishment to grow. It uses minerals that swirl up from the seabed, notably in storms. It uses carbon from the surface seawater, which can then absorb more CO2 from the air.

In dying, the little algae sink to the depths – the “long snowstorm” as Rachel Carson called it. This locks up carbon in the floor of the sea, perhaps for hundreds of years, in a process known as the biological pump of the carbon cycle.


Among the nourishing minerals that rise from the seabed, the global oceans are generally well-stocked with nitrates and phosphates. But iron is also essential for phytoplankton growth.

In the mid to north Atlantic, much of this is supplied in dust blown high across the ocean from the arid region of the Sahara. About 30 per cent of the dark southern oceans, remote from large land masses and helpful winds, is limited both in iron and blooms of algae.

Powered iron theory

The theory of fertilising these seas with powdered iron arrived in about 1990 in work by John Martin. It prompted a dozen or more seagoing experiments in which hundreds of kilograms of powdered iron, dissolved in acidified seawater, were dumped into southern surface waters over days, or sometimes weeks. This was followed by tracking and studying life in the parcels of enriched water.

The results were quite convincing, increasing the local growth rates of plant diatoms and shifting the phytoplankton into larger, chain-linked forms. These heavier diatoms and the carbonate shells of the zooplankton grazing on them were taken as potential for sinking more CO2.

The apparent promise of fertilisation was seized on by commercial ventures intending to exploit the technology to obtain carbon credits (or, as one major start-up founder put it, “to save the world and make a little cash on the side”).

Elon Musk, Tesla chairman and space entrepreneur, invested in and supported a 2008 project headlined "new plankton-seeding venture reaps $3.5 million". Another company busily sought patents for iron delivery systems.

"The reputability of these organisations," judged Tyler Rohr of the Massachusetts Institute of Technology, "ranged from a pirate-like disregard for scientific nuance . . . to an active engagement with the scientific community".

The fears of that heavyweight community about the hugely unpredictable and unintended consequences of changing the ocean's ecosystem brought protective action. In 2008 the London protocol, with support from the International Maritime Organisation, banned commercial fertilisation with iron as a form of ocean dumping.

In 2013 the United Nations formally recognised iron fertilisation as “geoengineering”, needing stricter prior assessment and approval. This followed freelance dumping of iron off the Pacific coast of Canada that precipitated a plankton bloom across some 10,000sq km.

The feasibility of fertilisation has prompted a 2019 proposal for production of dust-fine particles of iron by bacterial action in ponds ashore. This "biogenic" iron, mimicking the aeolian dust blown from continents, could be spread by air "when phytoplankton blooms are likely".


There is scepticism already about the real benefit of aeolian dust to growing phytoplankton and the sinking of enough carbon from iron fertilisation to any useful depths. As the National Academy of Sciences concluded, the unmeasured risks of doing it on any scale, in globally interlinked oceans, greatly outweigh the possible climate benefits.

Alleged ecosystem risks include disrupting marine food webs and fisheries, producing more algal blooms with toxic impacts and giving off greenhouse gases other than CO2. Bearing in mind the possible unintended consequences, as one oceanographer asks, “ how can we know when it’s going wrong?”

With scientific uncertainty still abounding, the present international moratorium on commercial ventures in fertilisation seems secure. But some scientists worry that if climate change becomes severe enough, key attitudes may change.

One fears that “the uncertainty of a geoengineered world [will be] seen as less catastrophic than the certainty of a climate changed world”; another that fertilisation “could be sold to a less informed public as an ethically viable gamble . . . particularly if developers highlight only positive outcomes”.

What seemed at one time to be a safely disarmed, even discredited, global proposition may still have its head above water.