Scientists warn against the high risk of degradation of marine ecosystems and human hardships.
An ambitious new study describes the full chain of events by which ocean biogeochemical changes, triggered by manmade greenhouse gas emissions, may cascade through marine habitats and organisms, penetrating to the deep ocean and eventually influencing humans. The study, led by the University of Hawaii and involving scientists from PML, was an international collaboration of 28 scientists from around the world and has been published in PLOS Biology.
Previous analyses have focused mainly on ocean warming and acidification, considerably underestimating the biological and social consequences of climate change. Factoring in predictable synergistic changes such as the depletion of dissolved oxygen in seawater and a decline in productivity of ocean ecosystems, the new study shows that no corner of the world ocean will be untouched by climate change by 2100.
“When you look at the world ocean, there are few places that will be free of changes; most will suffer the simultaneous effects of warming, acidification, and reductions in oxygen and productivity,” said lead author Camilo Mora, assistant professor at the Department of Geography in the College of Social Sciences at the University of Hawaii at Mānoa (UH Mānoa). “The consequences of these co-occurring changes are massive - everything from species survival, to abundance, to range size, to body size, to species richness, to ecosystem functioning are affected by changes in ocean biogeochemistry.”
Co-author Andrew Thurber, a postdoctoral fellow at Oregon State University, continued: “Other studies have looked at small-scale impacts, but this is the first time that we’ve been able to look the entire world ocean and how co-occurring stressors will differentially impact the earth’s diverse habitats and people. The real power is in the quantitative, predictive approach using the Intergovernmental Panel on Climate Change (IPCC) climate models that allow us to see how much it will all change, and also how confident we can be in our estimates.”
The human ramifications of these changes are likely to be massive and disruptive. Food chains, fishing, and tourism could all be impacted. The study shows that some 470 to 870 million of the world’s poorest people rely on the ocean for food, jobs, and revenues, and live in countries where ocean goods and services could be compromised by multiple ocean biogeochemical changes.
Mora and Craig Smith with UH Mānoa’s School of Ocean and Earth Science and Technology (SOEST) worked with the international collaboration of climate modelers, biogeochemists, oceanographers and social scientists to develop the study.
Jeroen Ingels at PML is one of the co-authors of the paper and as a member of the Network for Scientific Investigations of Deep-Sea Ecosystems (INDEEP, www.indeep-project.org), he was part of the expert consortium that developed the study. The group discussed climate change, ocean acidification and how the changes in the ocean would affect marine organisms and ecosystems, but crucially, formulating a method to quantify the important changes and potential effects on marine life and human welfare.
Jeroen commented: “The current rate at which anthropogenic emissions are still increasing is bad news for marine life and eventually, the millions of people that depend on the ocean in one way or another.
“Much of the climate change news in recent years has predominantly focused on themes such as sea level and temperature rises, but the totality of profound biogeochemical changes that are predicted to occur in our oceans will have far-reaching consequences.”
“The global spread of the projected changes will affect 100s of millions of people that have a relatively high dependence on ocean services such as food or income, and a large part of those live in low-income countries which may have little ability to adapt to the changes”
The researchers used the most recent and robust models of projected climate change developed for the Fifth Assessment Report of the IPCC to inform their analysis. They quantified the extent of co-occurrence of changes in temperature, pH, oxygen, and primary productivity based on two scenarios: a business-as-usual scenario wherein atmospheric CO2 concentrations could reach 900 ppm by 2100, and an alternative scenario under which concentrations only reach 550 ppm by 2100 (representing a concerted, rapid CO2 mitigation effort, beginning today).
They discovered that most of the world’s ocean surface will be simultaneously impacted by varying intensities of ocean warming, acidification, oxygen depletion, or shortfalls in productivity. Only a very small fraction of the oceans, mostly in polar regions, will face the opposing effects of increases in oxygen or productivity but even that is not good news.
“Even the seemingly positive changes at high latitudes are not necessary beneficial. Invasive species have been immigrating to these areas due to changing ocean conditions and will threaten the local species and the humans who depend on them,” said co-author Chih-Lin Wei, a postdoctoral fellow at Ocean Science Centre, Memorial University of Newfoundland, Canada.
The researchers assembled global distribution maps of 32 marine habitats and biodiversity hotspots to assess their potential vulnerability to the changes. As a final step, they used available data on human dependency on ocean goods and services and social adaptability to estimate the vulnerability of coastal populations to the projected ocean biogeochemical changes.
By 2100, global averages for the upper layer of the ocean could experience a temperature increase of 1.2 to 2.6°C, a dissolved oxygen concentration reduction of ~2% to 4% of current values, a pH decline of 0.15 to 0.31, and diminished phytoplankton production by ~4% to 10% from current values. The seafloor was projected to experience smaller changes in temperature and pH, and similar reductions in dissolved oxygen.
Of the many marine habitats analysed in the study, researchers found that coral reefs, seagrass beds and shallow, soft-bottom benthic habitats would experience the largest absolute changes in ocean biogeochemistry, while deep-sea habitats would experience the smallest changes.
Co-author Lisa Levin, a professor at Scripps Institution of Oceanography at the University of California, San Diego, notes: “Because many deep-sea ecosystems are so stable, even small changes in temperature, oxygen and pH may lower the resilience of deep-sea communities. This is a growing concern as humans extract more resources and create more disturbances in the deep ocean.”
“The deep-sea floor covers most of the Earth’s surface and provides a whole host of important ecosystem services including carbon sequestration in seafloor sediments, buffering of ocean acidity, and providing an enormous reservoir of biodiversity,” said Smith.
“Nonetheless, very little attention has been paid to modelling the effects of climate change on these truly vast ecosystems. Perhaps not surprisingly, many deep seafloor ecosystems appear susceptible to the effects of climate warming over the next century.”
“The impacts of climate change will be felt from the ocean surface to the seafloor. It is truly scary to consider how vast these impacts will be,” said co-author Andrew K. Sweetman, who helped to convene the original team of investigators and now leads the deep-sea ecosystem research group at the International Research Institute of Stavanger, Norway. “This is one legacy that we as humans should not be allowed to ignore.”