A groundbreaking study has put a price tag on the damage carbon emissions do to the world’s oceans, revealing that the global economic cost of climate change is nearly twice as high as previously calculated.
For years, the standard accounting of the “social cost of carbon” – a crucial metric used by governments to weigh the benefits of climate policy against the costs – has largely ignored the ocean.
Now, researchers from the Scripps Institution of Oceanography at UC San Diego have filled that gap.
In a study published in Nature Climate Change, the team introduced the “blue” social cost of carbon, integrating damages to coral reefs, fisheries, and coastal infrastructure into economic models for the first time.
The result is a shock to the system: when ocean impacts are included, the cost of every ton of carbon dioxide emitted into the atmosphere jumps by 91 per cent.
Pricing the invisible
“If we don’t put a price tag on the harm that climate change causes to the ocean, it will be invisible to key decision makers,” said environmental economist Bernardo Bastien-Olvera, who led the study.
“Until now, many of these variables in the ocean haven’t had a market value… This study is the first to assign monetary-equivalent values to these overlooked ocean impacts”.
The “social cost of carbon” is used by agencies like the U.S. Environmental Protection Agency to justify regulations. Excluding the ocean, the standard cost was estimated at $51 per ton of CO2.
The new study calculates that ocean-related damages add $46.20 per ton to that bill, bringing the total to $97.20 per ton.
To put that in perspective: globally, humans emitted an estimated 41.6 billion tons of CO2 in 2024. This implies that nearly $2 trillion in ocean-related damages occurred in that single year – costs that are currently missing from standard climate estimates.
Paying the price
Human-generated emissions harm the ocean in multiple ways, including warming, acidification, and oxygen depletion. These changes devastate ecosystems like kelp forests, mangroves, and coral reefs, while warmer temperatures fuel more severe storms that batter ports and coastal cities.
To calculate the cost of this destruction, the researchers looked at three categories of value:
- Market Use Values: Direct economic hits, such as decreased revenue from fisheries or diminished trade due to damaged infrastructure.
- Non-Market Values: Hidden costs, such as the health impacts on populations that lose access to seafood nutrition, or lost recreational opportunities.
- Non-Use/Existence Values: The “intangible” worth humans derive simply from knowing that biodiversity and healthy ecosystems exist.
By the year 2100, the study projects that market damages alone will cost society $1.66 trillion annually. The loss of “existence value” – the sheer enjoyment of nature – will cost another $224 billion, while decreased nutrition from failing fisheries will add $182 billion in losses.
Unequal burden
The study also highlighted a grim reality: the “blue” cost of carbon will not be shared equally.
Islands and small economies that are heavily dependent on seafood for survival will be disproportionately affected. As ocean warming reduces the availability of key nutrients in seafood – such as iron, protein, and omega-3 fatty acids – these populations face increased risks of disease and death.
“Protecting the environment can have high up-front costs, so we need methods for thinking about the trade-offs we are making as a society,” said co-author Kate Ricke, a climate scientist at Scripps.
The researchers hope that by revealing the true cost of emissions, policymakers and private companies will be compelled to reconsider the harm they are causing.
“When an industry emits a ton of carbon dioxide into the atmosphere, as a society we are paying a cost,” said Bastien-Olvera. “A company can use this number to inform cost-benefit analysis – what is the damage they will be causing society through increasing their emissions?”.
