“Up to now, the oceans have shielded us from the worst impacts of climate change by absorbing most of the heat caused by rising greenhouse gas emissions, and capturing around a quarter of the carbon dioxide released. The resulting ocean warming and acidification have added to other pressures on marine life, such as pollution and over-fishing, and the populations of many species are shrinking or shifting in response.
From the poles to the tropics, plankton, jellyfish, turtle, fish and seabird species are on the move, shifting by up to 10 degrees of latitude to find cooler habitats, while some breeding grounds for turtles and seabirds disappear.
The distribution patterns of species like pelagic tuna, Atlantic herring and mackerel, and European sprats and anchovies are gradually shifting in response to changing ocean temperatures. Some fish are moving tens to hundreds of kilometres per decade.
But not all species are able to cope.
Over the last three decades, as the planet has warmed, the frequency of coral bleaching has increased three-fold. In Western Australia, extensive areas of kelp forest were wiped out during a marine heatwave. In the Southern Ocean, progressive warming has been associated with a decline in krill, with populations of many seabirds and seals also decreasing.
“You worry about the polar bears; so do we. But nobody is worried about us, because we will lose our homes too with the melting ice and the rising sea level” – Anote Tong, Former President of Republic of Kiribati, the world’s lowest-lying island nation.
Ocean warming drives a chain of impacts that link to human society. Communities that rely on the ocean for daily subsistence – typically the poorest coastal nations – are likely to suffer the greatest losses. Ocean-based fisheries, tourism, aquaculture, coastal risk management and food security are all threatened by ocean warming combined with over-fishing and population growth.
‘The effects on food security are likely to be greatest in tropical and subtropical countries where the largest reductions in fisheries production are generally expected to occur. However, as profound as the effects of ocean warming on productivity of marine fisheries are likely to be in many of these countries, population growth and the quality of resource management will probably have a much greater influence on availability of fish per capital for the next few decades’ – IUCN report, Explaining Ocean Warming.
Oceans at the crossroads.
The report recommends a series of actions to address these impacts, including mitigating CO2 emissions, enhancing marine protected areas, and protecting the high seas and ocean seabed under the Law of the Sea and by expanding the World Heritage Convention.
‘We need to protect our oceans as if our lives depend on it – because they do’ – Sylvia Earle, ‘Ocean Elder’ and Founder, Mission Blue.”