By 2030, half the world's oceans could be reeling from climate change, scientists say

More than half the world's oceans could suffer multiple symptoms of climate change over the next 15 years, including rising temperatures, acidification, lower oxygen levels and decreasing food supplies, new research suggests.

By the mid-century, without significant efforts to reduce warming, more than 80 per cent could be ailing - and the fragile Arctic, already among the most rapidly warming parts of the planet, may be one of the regions most severely hit.

The study, published today in the journal Nature Communications uses computer models to examine how oceans would fare over the next century under a business-as-usual trajectory and a more moderate scenario in which the mitigation efforts promised under the Paris Agreement come into effect. In both scenarios, large swaths of the ocean will be altered by climate change.

Nearly all of the open sea is acidifying because of greenhouse gas emissions. But the researchers found that cutting greenhouse gas emissions could significantly delay future changes, giving marine organisms more time to migrate or adapt.

"Things that live in the ocean are used to regular variability in their environments," said lead study author Stephanie Henson, a scientist at the National Oceanography Centre at the University of Southampton in Britain. "It gets warm in the summer and it gets cold in the winter, and species survive that kind of range in temperature or other conditions perfectly well."

But she noted a warming climate could eventually cause changes in the ocean that have never happened before - hotter temperatures, lower pH or less oxygen than have ever naturally occurred. When this happens, some organisms may no longer be able to tolerate the changed conditions and will be forced to migrate, evolve as a species or face possible extinction.

There's a large degree of uncertainty in the scientific community about how organisms will react. But there's evidence to suggest major challenges ahead. Mass coral bleaching events in the past few years have been largely attributed to unusually warm water temperatures. Large-scale coral death on the Great Barrier Reef last year is thought to be strongly linked to climate change.

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