Coral reefs, shellfish, and even top predators such as tuna could be devastated as human carbon-dioxide emissions continue to acidify the world’s oceans. These and other impacts of anthropogenic ocean acidification are laid out in a new expert assessment, released today.
Oceans act as a huge carbon sink, sucking up much of the CO2 released to the atmosphere. But taking up more carbon increases the acidity of the water, with wide-ranging effects on marine organisms.
The authors of the report, released today from the Third Symposium on the Ocean in a High-CO2 World, review the current science on the effects on marine organisms, and write that there is a “medium confidence” level that shellfish harvests will decline. There is also a medium confidence level that economic damage will result from impacts on coral reefs, with tourism, food and shoreline protection suffering. The size of this is unclear but one estimate is for $1 trillion in damage from coral loss alone.
How larger species will fare as oceans acidify is less clear. The report gives only a “low confidence” rating to the idea that top predators and fin fish catches will be reduced. But any losses in this area could hit hard the 540 million people whose livelihoods depend on such fisheries.
Scientists also have a “very high confidence” that the ocean’s capacity to take up carbon decreases as waters acidify. So even larger cuts in human greenhouse gas emissions than currently envisaged may be needed to meet targets set to limit global warming as a result, the authors write.
The report is likely to be pored over by policymakers as it comes out ahead of the latest report from the IPCC’s working group II on the impacts of climate change, which is due next year. Although the new report was produced with a different methodology, it still represents one of the most comprehensive and up-to-date assessments of a major impact of CO2 emissions currently available.
Co-author Ulf Riebesell, an oceanographer at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, says more work is urgently needed to understand animals’ and plants’ abilities to adapt to a more acidic ocean, and to move researching the impact on single species to how ecosystems as a whole will fare. There is also a need to clarify on how these changes will affect the services that the oceans provide to humans — from food to protection from storms.
The report authors also say that the acidity of the oceans could increase by 170% by the end of the century, corresponding to a drop in surface ocean pH by 0.32. This occurs under a pessimistic scenario of high human emissions. Since the industrial revolution, surface ocean pH has dropped from 8.2 to 8.1. As pH is a logarithmic scale, the increase in acidity since the industrial revolution could reach around 170% under this scenario.
Under lower-emissions scenarios, this decrease would be around 0.07. But current emissions show no sign of dropping to those necessary to achieve such a goal, cautions Riebesell.
“If you look at current trajectories we’re no way below the [high emissions scenario],” Riebesell says. “Of course we hope the human race is smart enough to learn at some point and turn the wheel round.”