Proponents of modifying the ocean to battle climate change have rising hopes for their biomass sinking plans, but critics fear the environmental impacts
.jpg)
Entrepreneurial companies think sinking crop waste in oxygen-depleted waters could lock up carbon and help fight with climate change. The Black Sea is one location on their lists (Image: NASA / Dembinsky Photo Associates / Alamy)
Scientists and entrepreneurs from across the world gathered in Bucharest earlier this year to discuss a temptingly simple idea to battle climate change.
Gathering up plant scraps left over from agriculture and sinking them into the depths of the ocean could, they believe, take carbon that nature has locked up in plants and put it where it cannot escape.
Proponents believe the simplicity of the concept sidesteps some of the issues that have dogged other attempts to take geoengineering into the ocean. They are hoping a new standard defining how they should operate could fuel interest in this previously niche form of carbon removal. If it does, huge bundles of crop waste could one day be jettisoned from vessels in the Black Sea and the Gulf of Mexico, and money could flow to those doing it.
But significant questions remain about the environmental impact and how long carbon stored in this way will remain trapped. Opponents say geoengineering in general is a dangerous distraction from tackling climate change, and that the environmental impact of specific concepts – including this one – are often understated or underexplored in the rush to make money via the market for carbon credits.
The ocean for geoengineering
The ocean takes up somewhere between a quarter and a third of the current carbon dioxide emissions from fossil fuel burning and other sources, carbon dioxide that could otherwise be in the atmosphere, warming the planet. It has absorbed about 90% of the excess heat produced by these human activities too.
This outsized role in the climate system – and, more generally, the fact it covers most of the planet – makes it a tempting target for those who want to place a finger on the scales to tilt the Earth’s systems against warming.
Morgan Raven works on the carbon cycle at the University of California, Santa Barbara, in the US. She notes that studies of Cretaceous rocks show large deposits of organic matter in the ocean helped the Earth cool during a past “hothouse” event.
“This is how the Earth responds on a 100,000-year time scale,” she says. The question for geoengineers: “Can we make it a 100-year time scale so it’s useful for humans?”
Raven now works with Carboniferous, a company looking to sink agricultural waste, such as straw stalks and leaves, into the ocean. The concept was recently given the title Marine Anoxic Carbon Storage, or Macs, at that workshop in Romania.
While geoengineering via carbon dioxide removal has been criticised for distracting effort from emissions reductions, supporters cite the Intergovernmental Panel on Climate Change’s 2022 conclusion that carbon dioxide removal is “unavoidable if net-zero CO2 or GHG [greenhouse gas] emissions are to be achieved”.
