Dumping biomass in the ocean is not a climate solution

Arab News

15-04-2025

https://arab.news/9ew9x
Puro.earth, a self-appointed 'carbon removal certifier,' is seeking to establish a new accredited means of carbon sequestration: dumping bundled biomass (wood or crop waste) into the ocean. At least two companies are already selling carbon credits based on plans to dump biomass in the Black Sea. But 'ocean storage of biomass,' known as OSB, lacks scientific verification and highlights the risks of commercializing unproven climate interventions.
The idea is that 'degradation-resistant biomass' would be dumped into the Black Sea basin, where anoxic (oxygen-free) conditions would further slow, or even halt, degradation. As a result, the approach's proponents claim, the carbon would effectively be removed from the biological cycle for more than 1,000 years, with minimal environmental impact. But there is no scientific evidence that this is true.
While anoxic zones might appear barren, they are by no means devoid of life. And the tiny organisms found there — such as the Synechococcus bacteria, which was recently discovered in the Black Sea's anoxic basin — break down organic matter and release trapped carbon. They simply use chemosynthesis, rather than photosynthesis, to do it. Since carbon can migrate across the 'chemocline' (chemical transition zone) that separates anoxic zones from oxygen-rich waters, whatever is released within the Black Sea's anoxic basin can return to the ocean's carbon cycle and, ultimately, the atmosphere.
Two more processes could accelerate the release of carbon: dumping large quantities of baled biomass could — and likely would — induce turbulent chemical mixing in the chemocline, while the heat generated by decomposing biomass could further weaken the Black Sea's stratification. Moreover, as the ballast makes contact with the seafloor, it will likely resuspend sediment that currently acts as a reservoir not only of carbon, but also hydrogen sulfide (which is toxic) and methane (a highly potent greenhouse gas).
Whatever is released within the Black Sea's anoxic basin can return to the ocean's carbon cycle and, ultimately, the atmosphere
James Kerry and Lisa Levin
The seabed disturbance, together with the erosion of the chemocline, could cause these gases, in addition to carbon dioxide, to penetrate the oxygen-rich areas of the Black Sea, which support a diverse array of marine life, including dolphins, porpoises and many species of fish, some of which can be found nowhere else. Any expansion of the anoxic zone or intrusion of toxic gases into this habitat could severely harm its ecosystem, which is already under intensifying pressure from overfishing, pollution (including chemical, plastic and noise pollution), habitat destruction and rising temperatures.
But that is not all. The gases released as a result of OSB could ultimately make their way into the atmosphere, with potentially catastrophic consequences. This is not without precedent. When the stratification of Lake Nyos in Cameroon collapsed in 1986, large clouds of carbon dioxide gas were released, killing an estimated 1,700 people.
Puro.earth insists that OSB is safe. But these claims are based on modeling and short-term laboratory experiments, which cannot possibly replicate the unique and complex conditions of the Black Sea's anoxic basin. For one thing, these experiments tend to underestimate rates of organic degradation by failing to account for the possibility that they will increase over time — for example, as microbial communities adapt or due to a breakdown in the structural integrity of the biomass.
Moreover, while Puro.earth promises strict requirements for monitoring and environmental and social safeguards, it plans to observe the effects of its activities for only 15 years after the last biomass bundle is dumped — a far cry from the 1,000 years of carbon sequestration being claimed. Without long-term observational data, it cannot credibly claim that OSB is a legitimate — let alone benign — means of carbon removal, especially because the carbon permanency and ecological consequences of such activities are difficult to predict and even harder to monitor in such remote and poorly studied environments.
Land considerations further challenge the logic of OSB. Terrestrial biomass has value in itself, both in terms of the nutrients it contains and because there may be better uses for it, such as in the synthesis of biofuels. A complete life-cycle analysis of the OSB process suggests it involves significant energy consumption in the harvesting, processing, transportation and monitoring of the biomass. Puro.earth rightly asserts that any biomass used in the process 'must be free from harmful impurities and compounds,' such as toxins and pesticides. Yet that requirement would necessitate chemical testing of entire batches, which would likely impose significant costs.
Without long-term observational data, it cannot credibly be claimed that this is a legitimate — let alone benign — means of carbon removal
James Kerry and Lisa Levin
Even if OSB were safe and efficient, with dumped biomass remaining durably sequestered in anoxic waters, its promise as a climate intervention would be dubious. The problem is one of scale. According to the Intergovernmental Panel on Climate Change, we should be removing 6 to 10 gigatons of carbon dioxide from the atmosphere each year until 2050. Even assuming that only crop waste was used, locking up just one gigaton of carbon dioxide would require about 500 million tonnes of dry biomass, an amount comparable to the entire annual US corn harvest. This is not the only significant constraint on the proposed method; another is the paucity of anoxic zones on our planet to dispose of the biomass.
Companies that stand to gain financially from such projects should not be the arbiters of carbon-crediting mechanisms, nor are they qualified to make objective judgments about environmental safety. Under the UN Convention on the Law of the Sea, the standard has been, and always should be, one of precaution. A genuinely careful and conservative approach would be to conduct smaller-scale, multiyear controlled experiments before any large-scale, commercialized deployment were even to be considered.
The fact that OSB represents a low-tech approach to neutralizing carbon dioxide emissions does not exempt it from the precautionary principle and dumping regulations under the London Convention and London Protocol. The burden of proof is on the proponents of the intervention to demonstrate that their actions would not violate these standards. This should be reflected in any permitting decisions about OSB that countries bordering the Black Sea, such as Georgia and Turkiye, might have to make in the coming years.
Copyright: Project Syndicate