The damage to the world’s oceans from ongoing climate change is such that it effectively has  doubled the global cost of carbon dioxide emissions to society.

For the first time, a study from researchers at Scripps Institution of Oceanography at the University of California San Diego has integrated climate-related damages to the ocean into the social cost of carbon –  a measure of economic harm caused by greenhouse gas emissions.

Until now, the ocean was largely overlooked in the standard accounting of the social cost of carbon even though the degradation of coral reef ecosystems, economic losses from fisheries impacts and damage to coastal infrastructure are well documented and adversely impact millions around the globe.

“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 social cost of carbon is considered a more accurate accounting of harm than the calculations commonly used as the basis of carbon credits or carbon offsets offered to travellers. These calculations have been used by state governments and organizations such as the U.S. Environmental Protection Agency and Department of Energy to inform analyses of proposed policy actions to reduce greenhouse gas emissions.

Human-generated carbon dioxide emissions in the atmosphere cause damage by warming ocean temperatures, altering the chemistry of the ocean, reducing the ocean’s ability to hold oxygen necessary for species survival while increasing the severity of extreme weather, as rising temperatures provide more energy to feed extreme storms. These changes are altering the distribution of species and damaging ecosystems like coral reefs, mangroves, seagrass beds and kelp forests. There are also impacts to infrastructure like ports, which can be damaged from increased flooding and storms.

To develop the accounting, the study looked at straightforward market use values such as decreased fisheries revenue or diminished trade. It also accounted for non-market values such as health impacts of reduced nutrition availability from impacted fisheries and recreational opportunities at the ocean. Additionally, it considered intangibles such as the value of the inherent worth humans get from the enjoyment of ecosystems and biodiversity, which the researchers call non-use or existence value.

Researchers plugged the estimates into an economic model calibrated to varying greenhouse gas emission trajectories.

Without ocean impacts included, the social cost of carbon is $51 per ton of carbon dioxide emitted into the atmosphere. When the model is run with ocean impacts, study authors calculated an additional $46.2 per ton of carbon dioxide, reaching $97.2 total per ton of carbon dioxide, a 91% increase. For a sense of scale, in 2024, global carbon dioxide emissions were estimated to be 41.6 billion tons, according to the Global Carbon Budget analysis –  implying nearly $2 trillion in ocean-related damages associated with one year of global emissions, damages that are currently missing from standard climate cost estimates.

Overall, market damages are projected to be the largest cost to society, totalling global annual losses of $1.66 trillion in the year 2100. Damages in non-use values, the inherent worth we derive from enjoyment of ocean ecosystems, amount to $224 billion and non-market use values such as decreased nutrition from impacted fisheries adds up to $182 billion in annual losses.

But Bastien-Olvera, now an assistant professor at the National Autonomous University of Mexico, notes that a dollar of market damage is not the same as a dollar of cultural loss. These benefits are not perfectly substitutable, meaning that losses in one category cannot be fully offset by gains in another, so each category of damage carries a different meaning for society.

How the “blue” social cost of carbon will be an important tool for environmental decision makers

Study co-author Kate Ricke, a climate scientist and associate professor at Scripps Oceanography and the School of Global Policy and Strategy, added that social cost of carbon is a tool used in cost-benefit analysis, which is important for environmental decision makers. Cost-benefit analysis is used by government agencies for policy design and by members of the private sector for risk management analysis and financial planning.

“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 monetized and the ocean is particularly challenging to assign monetary values. The blue social cost of carbon is a new framework to recognize these values.”