In a climate crisis, is geoengineering worth the risks?

And the same month, a special report by the Intergovernmental Panel on Climate Change on the relative severity of different degrees of global warming included a section on geoengineering. It highlighted both the potential benefits and drawbacks of strategies such as stratospheric aerosols and ocean seeding(SN: 12/17/18).

Seeding the ocean

Ocean seeding, or iron fertilization, is unusual among geoengineering projects: Unlike most geoengineering proposals, ocean seeding has actually been tried in the real world. But the experiments also prompted a powerful response from environmental groups, effectively halting follow-up ocean seeding experiments.

Iron, a necessary ingredient for phytoplankton growth, is abundant on land, but limited in the open ocean. Scientists have long observed that dust blown into the ocean from the Sahara or ash from large volcanic eruptions can scatter iron-rich particles far out to sea, fueling brief but intense blooms. Phytoplankton draw carbon dioxide out of the air; when they die and sink to the seafloor, they carry the carbon down to the deep ocean, where it is sequestered away and can’t leak into the atmosphere.

Those observations prompted the late oceanographer John Martin of the Moss Landing Marine Laboratories in Florida to stand up at a conference in 1988 and famously quip: “Give me a half tanker of iron, and I will give you an ice age.”

Martin’s words kicked off a decade of iron fertilization research, culminating in a series of experiments in the mid-1990s known as IronEx. Scientists scattered iron across 12 separate 100-square-kilometer patches of ocean: four in the northwest Pacific Ocean, two in the equatorial Pacific and six in the Southern Ocean (SN: 9/30/95). The experiments were essentially a success: All 12 reported measuring as much as 15 times more chlorophyll — a measure of how much algae was present — in the waters after the experiment.

How much carbon was actually sequestered away by the blooms was less clear. Laboratory experiments suggested that as much as 100,000 metric tons of carbon per ton of iron added might be sequestered. Yet after several weeks of monitoring carbon export from the surface waters to deeper waters, the scientists estimated carbon sequestration to be only about 200 tons of carbon per ton of iron.

But those numbers are pretty uncertain, Buesseler notes. The researchers had limited time to monitor the carbon export, and were able to measure export only down to about 200 meters. Today, it would be possible to do the same experiments but with longer monitoring at deeper depths, he says, thanks to “gliders and floats and more ways to monitor the ocean without having to sit there on the ship.”

More harm than good?

Rising environmental concerns in the wake of IronEx have effectively prevented any follow-up scientific experiments. Some computer simulations of the effects of large-scale iron fertilization — on a much grander scale than the actual experiments — suggested that blooms in one location could create ocean dead zones elsewhere, or that the sinking carbon could acidify the deep ocean, threatening deep-sea marine life.

Noting the uncertainty, in 1999 the activist group Greenpeace urged the International Maritime Organization to ban dumping iron in international waters as industrial waste. A ban went into effect in 2006.

But iron fertilization and carbon sequestration still holds some allure as a commercial enterprise. In 2012, a group called the Haida Salmon Restoration Corporation struck a deal with a First Nations fishing village in western Canada to seed the ocean with 100 ton of iron sulfate — five times as much as previous experiments — in hopes that it would boost phytoplankton and therefore salmon populations. To help fund the project, the company planned to sell credits for the carbon dioxide taken up by the plankton. Although the Gulf of Alaska did see subsequent blooms and the salmon catch broke records that year, the company ran afoul of Environment Canada and sparked a debate about opportunistic geoengineering. Furthermore, whether the blooms were the result of the experiments was never proven.

In 2017, a related group called Oceaneos Marine Research Foundation proposed an iron fertilization experiment off the coast of Chile. So far, protests by scientists and environmental activists have scuttled those plans.

To Buesseler, these attempts further highlight the need for formal protocols within government-sponsored research projects into ocean seeding. “Without regulations, you can get a rogue country or individual who goes out and does it.”

A snowball’s chance

Unprecedented risks posed by climate change over the next few decades may require a willingness to at least consider even seemingly absurd geoengineering ideas, says climate scientist Anders Levermann.

In July, Levermann and colleagues at the Potsdam Institute for Climate Research in Germany  noted in Science Advances that ice loss from the West Antarctic ice sheet is accelerating; some studies suggest the ice sheet is already past the point at which reducing greenhouse gas emissions will stop its collapse.

Even without that collapse, climate projections suggest that sea levels will rise by between 0.3 meters and 1.2 meters by the end of the century  (SN: 8/5/19). Depending on possible — and still-debated — contributions from ice cliff collapse, global average sea level could rise as much as 2.4 meters (SN: 2/6/19). That would put many coastal cities, including much of New York, London and Rio de Janeiro, under water.

So Levermann and his colleagues decided to run a thought experiment: What if people sprayed trillions of ton of snow over the West Antarctic ice sheet? Would that save it? Added snow, the team found, might stabilize the ice sheet by replacing ice being lost on its underside to melting by warmer ocean waters.

Calculations showed that the project would require 7.4 trillion tons, or about 7,400 cubic kilometers, of seawater, pumped over 10 years to produce the water for the snow. To power the seawater pumps and snow cannons, the project would require at least 12,000 wind turbines, placed in the Southern Ocean. More power might also be required to desalinate the water and keep it from freezing in the pipes.

Levermann notes that his team isn’t advocating for the plan, just providing a sense of the scale of such a project. It would be a moon landing–sized effort, he says, and the collateral damage to the Southern Ocean habitat from wind turbine installation would likely be significant. And the plan would not be a permanent fix, but it would buy time for coastal communities to prepare for rising seas or to relocate.

Reopening Pandora’s box

Yang proposes providing some $800 million to NASA, the Department of Defense and the National Oceanic and Atmospheric Administration to research geoengineering. “In a crisis, all solutions have to be on the table,” he said September 4 at a nationally televised CNN town hall on climate change. But geoengineering’s many potential pitfalls haven’t made it popular with the other Democratic presidential candidates, whose climate platforms focus instead on ways to reduce U.S. reliance on fossil fuels.

Buesseler acknowledges that when it comes to real-world experiments, the needle has hardly moved since 2007, when he helped convene a symposium at WHOI to discuss the status of ocean seeding.

But “I’ve always expected this would come back up,” he says. “Once you open the box, the idea is out there.”