As carbon emissions continue to climb, is geoengineering our best hope to hinder the melting of the Greenland and Antarctic ice sheets, preventing significant sea level rise? A recent analysis of five major geoengineering proposals suggests otherwise.

Martin Seegert from the University of Exeter in the UK warns that promoting unworkable geoengineering solutions distracts from pressing issues. “This undermines our urgent need for decarbonization,” he asserts.

Seegert and his team assessed each polar geoengineering proposal using six criteria: effectiveness, scalability within a reasonable timeframe, affordability, international consensus, potential to create false hope for decades, and environmental risks.

In Antarctica, various ice sheets rest on the seabed, and they are melting from below due to warm seawater. One proposed solution involves erecting large “curtains” to block warm currents from reaching these ice sheets and the floating ice shelves that protect them.

The team warns that the effectiveness of these curtains is uncertain, as noted by Stephen Chaun from Monash University, Australia. “If hot water is diverted away from one ice shelf, where does it go next? Redirecting it to a nearby shelf just shifts the problem,” he states.

These curtains would need to be anchored to the seabed at depths of up to 1 kilometer, rising hundreds of meters and extending for tens of kilometers.

A significant portion of the research voyage to Antarctica is being refocused due to the hazards posed by icebergs and sea ice. “That presents considerable danger,” he notes.

Chown mentions that currently, only a single ship is capable of reaching the area where ocean curtains are required to safeguard Thwaites’ “Doomsday” glacier.

Concerns arise for glaciers that sit on land rather than floating on the seabed, as increased liquid water underneath the ice can act as a lubricant, speeding up the flow and leading to heightened sea level rise.

One proposed intervention is to drill holes in the ice and pump out any water beneath it.

“This approach necessitates a multitude of holes drilled into potentially thick ice. However, we lack precise knowledge of where the water lies,” says Sammy Buzzard from Northumbria University, UK. “Even with an understanding of the science, scalability, cost, and power supply issues make this an impractical solution.”

Another concept involves covering the Arctic Ocean’s surface with tiny hollow glass beads to reflect solar heat back into space. However, Chaun warns, “[This] could backfire completely.”

Sustaining this coverage would require the production of 360 megatons of glass beads annually—comparable to global plastic output. Following lab tests revealing the beads were toxic, the project aimed at testing this idea was discontinued.

Stratospheric aerosol injection is another proposed method, which involves releasing substances like sulfur dioxide into the stratosphere to form aerosols that reflect sunlight. This method poses significant challenges beyond just polar regions. Aerosols would not only fail to stay within the polar stratosphere but also provide minimal effectiveness during the dark polar winters against reflective ice and snow.

The scale of aerosol deployment would necessitate vast quantities, potentially damaging the ozone layer and disrupting climates in other regions, as noted by Valérie Masson-Delmotte from Paris-Saclay University, France. Affected countries may even seek compensation.

Another suggestion includes thickening Arctic sea ice by pumping seawater over it. “This would necessitate deploying millions of devices across drifting, fragile ice,” remarks Heidi Sevestre from Norway’s Arctic Surveillance and Assessment Program. “Such a scenario is technically, logistically, and economically unfeasible.”

The final concept evaluated by the researchers revolves around fertilizing the Southern Ocean to boost phytoplankton growth, thereby absorbing carbon as organic matter settles to the seabed. However, out of 12 small tests, none effectively reached the seabed. Furthermore, this approach could accelerate ocean oxygen depletion and release potent greenhouse gases like methane and nitrous oxide, warns Masson-Delmotte.

“I’m deeply worried about the overly optimistic views presented by some proponents of these strategies, which often gloss over the challenges,” states Masson-Delmotte. “I believe this article highlights that gap.”

Seegert argues that pursuing further research into these ideas squanders valuable resources. “The scale challenges are insurmountable,” he asserts.

Yet, not all researchers agree. “I believe it’s premature to dismiss any of these approaches entirely,” comments Shawn Fitzgerald from the Climate Restoration Centre in Cambridge, UK.