Scientists has – for the first time – factored climate-driven damage to the ocean into the social cost of carbon – a key metric used to estimate the economic harm caused by greenhouse gas emissions, with profound implications.

After decades of calculating the economic cost of climate change largely on land, scientists at Scripps Institution of Oceanography at the University of California San Diego have found that by integrating the ‘blue’ social cost of carbon, the true cost of carbon dioxide emissions to society has nearly doubled.

Despite the mounting evidence of coral reef collapse, declining fisheries, and escalating damage to coastal infrastructure, many of the pressures being faced by the ocean have – until now – remained invisible in economic models. However, by now assigning monetary values to these impacts for the first time, this new framework exposes the scale of losses borne by marine ecosystems – and by the people who depend on them.

“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 during a postdoctoral fellowship at Scripps Oceanography.

“Until now, many of these variables in the ocean haven’t had a market value, so they have been absent from calculations. This study is the first to assign monetary-equivalent values to these overlooked ocean impacts.”

The findings, published on January 15 in Nature Climate Change, arrive at a moment when governments and industries worldwide are reassessing the real cost of carbon pollution. Social cost of carbon is already used by agencies such as the US Environmental Protection Agency and Department of Energy to evaluate climate policies, making the inclusion of ocean damage a potentially transformative shift.

Ocean carbon accounting

Carbon dioxide emitted by human activity does not stay in the sky. It is absorbed by the ocean, warming seawater, altering its chemistry, reducing oxygen levels and intensifying extreme weather. These cascading changes are reshaping marine life and damaging habitats including coral reefs, mangroves, seagrass meadows and kelp forests, while rising seas and stronger storms threaten ports and other coastal infrastructure.

To quantify this web of impacts, the researchers examined how societies rely on the ocean for food, trade, recreation and cultural identity. Their accounting included market losses such as reduced fisheries revenue and disrupted shipping, as well as non-market values such as diminished nutrition and fewer recreational opportunities. They also incorporated what they describe as non-use or existence values – the inherent worth people place on thriving ecosystems and biodiversity, even when they are not directly used.

These estimates were then fed into an economic model that simulates different future emission pathways. Without ocean impacts, the social cost of carbon stands at US$51 per tonne of carbon dioxide. With ocean damage included, the study adds a further US$46.2 per tonne, bringing the total to US$97.2 – a 91% increase.

Against the backdrop of 41.6 billion tonnes of global emissions in 2024, the researchers estimate this represents nearly US$2 trillion in ocean-related damages in just one year – costs that are currently missing from standard climate accounting.

Looking ahead to 2100, the study projects that market damages will dominate, reaching US$1.66 trillion annually. Non-use values linked to the enjoyment and existence of ocean ecosystems amount to US$224 billion, while non-market impacts such as reduced nutrition from fisheries losses contribute a further US$182 billion.

Yet Bastien-Olvera cautions against treating all dollars as equal. Cultural loss, food security and ecosystem collapse cannot simply be traded off against financial gains elsewhere.

Study co-author Kate Ricke, a climate scientist and associate professor at Scripps Oceanography and the School of Global Policy and Strategy, has emphasised that social cost of carbon underpins cost–benefit analysis – a cornerstone of both public policy and private-sector decision making.

“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 Ricke, who led a 2018 study that estimated country-level contributions to the social cost of carbon.

“There are things that people value and benefit from that aren’t easily monetised and the ocean is particularly challenging to assign monetary values. The blue social cost of carbon is a new framework to recognize these values.”

The study also reveals a starkly uneven geography of harm. Small island states and coastal economies emerge as some of the most vulnerable, in part because of their heavy dependence on seafood for nutrition. As warming seas reduce the availability of key nutrients such as protein, iron, calcium and omega-3 fatty acids, the resulting dietary losses are projected to increase disease risk and mortality.

For Bastien-Olvera, bringing together fisheries scientists, reef and mangrove experts, biological oceanographers and economists has been essential to the work. It’s his hope that the framework will now be taken up by governments and industry alike.

“The social cost of carbon can help you contextualise the costs of climate change,” said Bastien-Olvera. “When an industry emits a ton of carbon dioxide into the atmosphere, as a society we are paying a cost. A company can use this number to inform cost-benefit analysis – what is the damage they will be causing society through increasing their emissions?”

Funded by the Scripps Institutional Postdoctoral Fellowship and involving researchers from institutions including UC Santa Barbara, the University of British Columbia, the University of Oxford and the European Institute on Economics and the Environment, the study offers a powerful new lens on the true cost of carbon and brings with it the ocean into greater focus.

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