Our effects on the oceans have yet to make themselves truly felt

The oceans are warming and acidifying at an accelerating rate, but other adverse changes are also under way because of climate change. Several of these other changes, including ones to ocean microbes that regulate Earth’s carbon and oxygen cycles, will increasingly have their impacts felt in coming decades, say the authors of a new study.

The scientists, who work at Princeton University in the United States, examined physical and chemical changes taking place in the oceans as a result of a rise in atmospheric CO2 fueled by our emissions. They then applied diagnostical tools to map the emergence of anthropogenic impacts on various timescales. “We found emergence timescales that ranged from less than a decade to more than a century, a consequence of the time lag between the chemical and radiative impacts of rising atmospheric CO2 on the ocean,” they write.

“Processes sensitive to carbonate chemical changes emerge rapidly, such as the impacts of acidification on the calcium carbonate pump (10 years for the globally integrated signal and 9–18 years for regionally integrated signals) and the invasion flux of anthropogenic CO2 into the ocean (14 years globally and 13–26 years regionally),” the researchers explain.

“Processes sensitive to the ocean’s physical state, such as the soft-tissue pump, which depends on nutrients supplied through circulation, emerge decades later (23 years globally and 27–85 years regionally),” they add.

In other words, processes affected by gradual changes in the climate and ocean circulation because of a build-up of CO2 in the atmosphere will take from three decades to a century to manifest themselves. These changes will impact nutrient supplies and the cycling of carbon through marine plants and animals.

The oceans absorb excess heat and carbon from the atmosphere, but they do so at a cost to themselves: in the process their waters warm and acidify, which impacts marine ecosystems. Acidification and warming can harm microbes at the base of the marine food web that feeds fish and coral reefs, produce oxygen and help lock up CO2 from the atmosphere.

“Our results indicate that many types of observational efforts are critical for our understanding of our changing planet and our ability to detect change,” says Sarah Schlunegger, a research associate at Princeton’s Program in Atmospheric and Oceanic Sciences.