No Good News for Oceans As Climate Changes

We often hear about melting sea ice, rising tides and bleached coral reefs, but climate change is poised to reverberate through a broader swath of the marine environment than these headline issues alone might suggest.

According to a new study published in PLoS Biology, “the entire world’s ocean surface will be simultaneously impacted by varying intensities of ocean warming, acidification, oxygen depletion, or shortfalls in productivity.” As the ocean’s biogeochemistry shifts, the paper reports, so too will its habitats and the creatures living there. This could mean hardship for some 470 to 870 million people–many of whom live in poverty–who depend upon the bounty of the sea to support livelihoods and fill dinner plates. And these impacts are not predicted to occur centuries down the road, either: according to the study, they may transpire as soon as 2100. 

Nearly 30 scientists from around the world–including climate modelers, ecologists, biogeochemists and social scientists–co-authored the study. They built upon computer models from the Intergovernmental Panel for Climate Change by compiling data from 31 Earth System Models that included at least one ocean parameter. All told, 27,000 years’ worth of data of the various overlapping, aggregated variables were compiled into their new model.

With those data compiled, they then modeled two different future scenarios: one in which atmospheric carbon dioxide concentrations increase to 550 parts per million, and another in which they hit 900 ppm (the planet currently stands at about 400 ppm, as compared to pre-industrial times, when that measurement was 280 ppm). The former model represents values predicted if mitigation efforts are undertaken, while the latter is predicted for a “business-as-usual” scenario where we maintain current levels of greenhouse gas emissions into the future.  

Their model predicted changes in temperature, oxygen levels, increased acidity and productivity (the creation of organic compounds by primary producers like phytoplankton) on both the ocean surface and the sea floor under those two future scenarios. Nearly across the board on the ocean’s surface, they found, their models predicted a continued warming and rise in acidity accompanied by a decline in oxygen and productivity. The only exception was in a small fraction of the sea in polar regions, where the sea surface would experience increased oxygen and productivity. The magnitude of these predicted changes, they write, will be greater than any comparable shifts over the past 20 million years.

The most drastic impacts, they found, will occur on the ocean’s surface, but the seafloor will also experience its share of smaller but still significant changes. Seafloor temperature and acidity will change only slightly compared to the surface, but there will be large reductions in the influx of carbon, which provides food for many bottom-dwelling organisms. The drop in dissolved oxygen on the sea floor will be similar to that experienced on the surface.

These changes may be enough to disrupt the ocean floor’s delicate ecosystem. ”Because many deep-sea ecosystems are so stable, even small changes in temperature, oxygen, and acidity may lower the resilience of deep-sea communities,” Lisa Levin, an oceanographer at the University of California, San Diego, and co-author of the paper, said in the release. “This is a growing concern as humans extract more resources and create more disturbances in the deep ocean.” 

As for the surface, the magnitude of the projected changes will vary by place. The tropics will experience the smallest changes in acidity; temperate regions will suffer the least significant shifts in temperature and productivity; and the Southern Ocean near Antarctica will be spared the least fluctuations in oxygen. But overall, across the board the ocean surface will suffer significant impacts.

With those data in hand, they then overlaid habitat and biodiversity hot spot information for 32 diverse marine environments around the world to see how these changes would impact ocean flora and fauna. Coral reefs, seagrass beds and other shallow areas will suffer the greatest impacts, they found, while deep ocean seamounts and vents will suffer the least.

Humans will not be spared the repercussions of those changes. In a final analysis, they quantified humanity’s dependence on the ocean by analyzing global jobs, revenues and food that comes from the sea. Most of the up to 870 million people who will be affected most by these changes live in some of the world’s poorest nations, they found.

While these predictions are subject to the same limitations that plague any computer model that attempts to represent a complex natural system and project its future fate, the authors believe that the results are robust enough to strongly support the likelihood that our oceans will be very different places in the not-too-distant future. If carbon dioxide levels continue to rise, they write, “substantial degradation of marine ecosystems and associated human hardships are very likely to occur.”

“It is truly scary to consider how vast these impacts will be,” co-author Andrew Sweetman of the International Research Institute of Stavanger, Norway, emphasized in the press release. “This is one legacy that we as humans should not be allowed to ignore.”

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.