Beware ‘blue carbon’ bold, but uncertain claims

As originally published on Newsroom, July 11 2023

Audacious assertions about the oceans’ potential for carbon sequestration are not yet matched by reality

Forests of seaweed grow much faster than forests of trees and so absorb carbon dioxide far more rapidly. That is leading to some bold claims for the potential for seaweed to solve climate change. And it’s being matched with bold actions – Microsoft, Shopify and Stripe are already buying seaweed-based carbon removals.

Is this boldness justified?

The biggest challenges do not always bring out the best in people, companies, or nations. There is an inevitable temptation to make bold claims based on little evidence, especially when disproving those claims is hard. This temptation keeps being realised for claims about emissions and emissions reductions.

The best solution, as always, is solid science that reveals the truth of those claims. That science takes time. That creates a gap between claims and truth that allows for hogwash to proliferate.

The methane leakage discrepancy

A clear example from the past year has been leakage of methane from natural gas wells and plants. Methane has a high global warming potential so leaks are bad. The natural gas industry for decades claimed low rates of leakage. The International Energy Agency estimated that globally 1.7 percent of methane leaked from wells and plants. The oil and gas industry could make the simple argument that leaks would cost them money and that they were good global citizens, so their plants would be well-maintained with minimal leakage. In the absence of credible monitoring, those claims stood unchallenged.

However, scientists could observe the overall amount of methane in the atmosphere. For many years, that top-down view of methane levels conflicted with the bottom-up accounting based on reported methane emissions from oil and gas leaks, and other anthropogenic sources.

So what caused this gap? Had researchers missed a large natural source or sink of methane? Was methane from livestock far in excess of what we understood? Or were some people lying?

The gap was resolved once independent monitoring became possible – in this case the monitoring is by a new generation of space-based sensors that allow the detection, location, and quantification of plumes of leaking methane. As cynics might expect, the industry was being far from honest. The actual rate of leakage from the oil and gas industry was far higher than 1.7 percent; in fact a single leak in Turkmenistan produced emissions equivalent to the whole of France. Globally, methane leaks have turned out to be about twice what the industry claimed, with a global warming impact potentially equivalent to Canada’s.

Rainforest carbon offsets: a cautionary tale

The same pattern has played out for rainforest carbon offsets. To meet the demand from companies for their products to be carbon neutral, those companies buy rainforest protection – preventing those forests from being chopped down and preventing the emissions that would result. Or at least those are the bold claims, backed and certified by organisations which say they represent leading carbon standards for offsets.

When independent researchers explored the claims of projects that said they were protecting rainforests, many showed no evidence of reducing deforestation or were in areas where the rainforests were not at risk, so there was no benefit from the claimed protection. Again, remote sensing has played a role with satellite imaging helping to validate ground-based monitoring.

This year has seen those certifying organisations called out for verifying implausible claims. One estimate was that 94 percent of offsets to protect rainforests had no effect on those rainforests.

The pattern goes like this: well-intentioned people want to make a difference with projects that have uncertain outcomes, where bold claims are easy to make yet hard to disprove. Those claims attract further well-intentioned investment so those projects keep growing… until the research is finally done to call out claims that are at best overly hopeful.

What’s the next climate solution that may succumb to this pattern? Enter ‘Blue carbon’.

This refers to the carbon processed and stored in our oceans and coastal regions. These enormous ecosystems contain far more carbon than our atmosphere, suggesting a golden opportunity for climate change mitigation. But, as with rainforest offsets, blue carbon projects are making audacious claims while a fair bit of scientific uncertainty remains.

Sea-based scientific uncertainties

Mangroves, tidal marshes, and seagrass meadows are the best-understood ecosystems. Projects protecting and regenerating these areas are already selling carbon offsets with claims that such initiatives could absorb a gigaton of carbon dioxide annually – a handy contribution given humanity’s carbon emissions hover at around 40 gigatons each year.

Even for these projects, the effects of human intervention are often unclear. How much carbon impact we can have and at what cost is uncertain. And then there’s the tricky matter of monitoring and ensuring the carbon stays where it should – permanently in storage.

Less well understood are seaweed forests, fiords, and the seabed. Increasing seaweed farming could sequester large amounts of carbon, but could also reduce phytoplankton growth in the same waters for no net change of carbon uptake. Aotearoa’s seabeds sequester plenty of carbon and Fiordland in particular exports a great deal of carbon from land to the ocean bed. Protecting seabeds from bottom trawling could prevent losses of carbon from sediments but monitoring of the effects of trawling on the seabed is woefully inadequate so understanding the impact of reduced trawling is difficult.