Changing Oceans in a Changing World – World Oceans to Undergo Massive Changes by the Turn of the Century

Jenny Griffin

There is increasing public awareness to the perils of rising atmospheric CO2 levels as a result of burning fossil fuels for energy, and the impact this is having on our climate. Yet surprisingly, the side effects of rising CO2 levels are rarely discussed, even though these impacts are significant and will have severe consequences for humankind if left unchecked.

The oceans cover two thirds of the Earth and are an important source of food and other resources. Any impact to ocean productivity will impact human livelihoods and possibly even survival.

A comprehensive analysis of oceanic biogeochemical changes predicted to occur by the end of this century as a result of anthropogenic greenhouse gas emissions is described in a new study published in PLoS Biology (15th October 2013). The study highlights how these changes will trigger a knock-on chain of events that will spread throughout ocean habitats, from inshore coastal zones to the depths of the ocean, impacting marine organisms small and large, and ultimately humans who depend on these habitats and organisms.

Previous studies tend to focus primarily on the impacts of ocean warming and acidification, with not enough consideration given to the biological impacts that biogeochemical changes will have on marine ecosystems, nor seriously considering the social impacts of these effects.

The researchers factored predictable synergistic changes, such as oxygen depletion and declining ocean productivity, into their models; the results of their analysis show that the entire world ocean will be affected by climate change by the end of the century, with no region remaining untouched.

“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.

The researchers illustrate that the consequences of these changes to human populations are likely to be astronomical and disruptive. As entire marine food webs will be affected, humans will have a reduced source of food, fishing and tourism industries are likely to be severely affected, and there will be social and economic impacts as a result. An estimated 470-870 million people from some of the poorest nations in the world who depend on the ocean for a source of food, for jobs and for economic security, are at grave risk of losing their source of food and source of income by 2100 as a result of multiple biogeochemical changes that are taking place within the oceans.

Using climate models developed for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) to perform their analysis, the research team determined that the majority of the ocean's surface will be simultaneously impacted by varying degrees of ocean acidification, warming, oxygen depletion, and reduced productivity. No oceanic region in the world will experience cooling or an increase in alkalinity, but a tiny fraction – predominantly polar waters – may experience an increase in dissolved oxygen or an increase in productivity.

Once the researchers had collated the above data, they proceeded to assess the impact of predicted biogeochemical changes on productivity and biodiversity, looking at global distribution maps that included 32 marine habitats and biodiversity hotspots. Finally, to determine the vulnerability of coastal human populations to these predicted changes, they included current data on human consumption of marine resources and human dependence on ocean services, together with an indication measure of the ability of these human populations to socially adapt to the predicted 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 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 of the International Research Institute of Stavanger, Norway. “This is one legacy that we as humans should not be allowed to ignore.”

References:

Chase J (2013) A Sea of Change. PLoS Biol 11(10): e1001683. doi:10.1371/journal.pbio.1001683

Mora C, Wei C-L, Rollo A, Amaro T, Baco AR, et al. (2013) Biotic and Human Vulnerability to Projected Changes in Ocean Biogeochemistry over the 21st Century. PLoS Biol 11(10): e1001682. doi:10.1371/journal.pbio.1001682