Warming oceans will affect the poorest

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A fisherman in Elmina, Ghana: Livelihoods are threatened by ocean warming. Image: Steve Evans via Wikimedia Commons

Livelihoods like this Ghanaian fisherman’s are threatened by warming oceans.
Image: Steve Evans via Wikimedia Commons

By Tim Radford

By 2100, the world’s oceans will be warmer and more acidic, with less dissolved oxygen and lower yields of fish and shellfish. And that will make life very difficult for up to 870 million of the world’s poorest people who rely on the sea for food, jobs and income.

LONDON, 22 October - Camilo Mora of the University of Hawaii and colleagues report in the journal Public Library of Science Biology that greenhouse gas emissions from industry and power generation have begun to trigger biogeochemical changes in the oceans that will impose huge costs.

These changes are likely to cascade through marine ecosystems and habitats to the deep ocean itself, and to affect humans along the way.

“The consequence 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,” said Dr Mora.

Mora and fellow oceanographers made headlines earlier this month by calculating the year in which any location on Earth was likely to experience dramatic and inexorable climate change: the researchers arrived at a mean date of 2047 (give or take six years on either side) for change, with the first impact in West Papua by 2020.

The PLOS Biology paperonce again tries to take a global view of change on the blue planet. The researchers calculated the effect of two scenarios for the future: one in which the world rapidly tries to reduce emissions, and the notorious business-as-usual scenario, which will take carbon dioxide concentrations to the unprecedented level of 900 parts per million by 2100.

No cooling

Then they contemplated the impact on 32 marine habitats and biodiversity hotspots, and then they examined the available data on human dependence on the ocean.

They found that most of the world’s ocean surface would feel the heat. Only in the polar regions would there be any increase in productivity or in oxygen levels. Nowhere would there be any cooling, and pH levels would trend towards acidification everywhere.

By 2100 global averages for the upper layer of the ocean would increase by between 1.2°C and 2.6°C. Dissolved oxygen concentrations would on average fall by between 2% and 4%, and phytoplankton production would diminish by between 4% and 10%. Phytoplankton are the base of the ocean food chain, so this can only reduce overall yield for between 470 and 870 million people who make a precarious and meagre living from the sea.

“The impact of climate change will be felt from the ocean surface to the sea floor,” said Andrew Sweetman, a co-author, now at the International Research Institute of Stavanger, Norway. “It is truly scary to consider how vast these impacts will be. This is one legacy that we as humans should not be allowed to ignore.” - Climate News Network