When the ocean is dying, the planet too

In the middle of the exhibition hall of the International Union for Conservation of Nature (IUCN) Congress, held in Hawaii, is a very large world map of the US Ocean and Meteorological Agency (NOAA). It has had great success with the public by showing in acceleration the warming of the ocean, as well as the increase in its salinity since the end of the twentieth century: the planet turns to scarlet.

And the gigantic oceanic mass that covers 71% – or 360.6 million square kilometers – is expected to gain one to four degrees by 2100. Even the temperature of the deep water is in the process of and, near the coast, the thermometer climbs 35% faster than in the high seas since the 1960s.

“Changes in the ocean are five times faster than in any terrestrial ecosystem,” said Dan Laffoley, vice president of IUCN’s World Commission on Protected Areas.

Scientists estimate that the ocean has absorbed 93% of the warming due to greenhouse gas emissions generated by human activities since 1970. “Otherwise, it would be 36 degrees Celsius more than it currently is on Earth, it would be unbearable, “says Carl Gustaf Lundin, Director of IUCN’s Marine Program. But “70% of biodiversity is in the ocean,” he recalls. This buffering role in the face of climate change has a high cost for marine ecosystems, which is what the network of nature defense shows in a voluminous compilation of scientific studies, it makes public Monday, September 5. Eighty scientists from twelve countries contributed to this sum – unprecedented in size. The painting is edifying.

Migrations of marine organisms

“Changes in the ocean are five times faster than in any terrestrial ecosystem,” said Dan Laffoley, vice chair of IUCN’s World Commission on Protected Areas and a key co-author. From polar regions to tropical regions, entire groups of species, such as jellyfish, turtles and seabirds, have begun to rise ten degrees of latitude to the poles.

All marine organisms have begun to migrate: phytoplankton, algae, invertebrates, fish, but not all along the same path. Not only has plankton, at the base of the marine wildlife food chain, been changing ranges for fifty years, but its seasonality is changing, and it is becoming smaller in places. More positive note: it diversifies in cold waters.

These new data have “dramatic” effects, the authors insist, on the reproduction and nutrition of many species. For example, global warming has a devastating effect on turtles, with six of the seven marine species classified by IUCN as endangered. Among other diseases, it disrupts the incubation of eggs, dangerously increasing the number of females, to the point of compromising the next generation.

Some phenomena are known: coral bleaching is a clear indicator, visible to the naked eye, the warming and acidification of water. All of them are expected to be affected by 2050, as they provide habitat for a quarter of the fish species. It is harder to educate the public about the fate of algae, although scientists are equally worried about accelerated degradation of coastal funds. The destruction of kelp forests causes some fish to be lost and, even worse, their habitat, while promoting the proliferation of other algae, which reduces the amount of oxygen in the water.

Impacts on human health

Near the coast, the changes will have obvious impacts. Some populations are dependent on seafood. Fishing and aquaculture provide about 15% of animal protein to 4.3 billion people worldwide. However, under the effect of rising temperatures – to which are added attacks of jellyfish and various pathogens – shellfish farms, crustaceans or salmon will be moved. As for the inshore fishermen, there will be winners and losers among them. In Somalia, for example, particularly poorly endowed, the fishery could go from 1.29 kg to 0.85 kg of fish per person per year.

In comparison, in the Pacific islands, where the waters are very rich, the average consumption is around 35 kg per person and provides up to 90% of animal protein to their inhabitants. Resources could decrease by 20% by 2050. But the problem in this part of the world lies mainly in the destruction of corals. This leaves the field free for dinoflagellates, phytoplankton on which toxins develop, graze herbivorous fish and end up concentrating in large predators, such as groupers. There has been a real “epidemic” of ciguatera in French Polynesia in recent years, the report says.


It devotes a particularly chilling chapter to the impacts of these mutations on human health. “More heat, less oxygen, more microbes,” says Laffoley. The passages that open between the Atlantic and the Pacific with the melting ice will not only be a boon for freight and cruise organizers. Invasive species will themselves be able to circulate more, viruses too. More numerous, pathogens also see their circulation favored by rising sea levels, which accelerates exchanges with terrestrial bacteria in estuaries.

In general, the shorelines appear more and more vulnerable, not only because of rising sea levels. The complex relationships that closely link ocean and climate play a role in increasing the strength of storms. But humans have altered many natural protective barriers, such as mangroves, 30% of which have disappeared in a century. Once again, the warming has aggravated these destructions.

Much remains to be done for human societies to measure the “greatest hidden challenge of our generation,” according to the report’s authors. Beyond the marine world, it is the entire planet that will be upset by the changes in progress. “The ocean has a capacity for resilience, you have to help it,” says Lundin. Despite its vital role for the planet and human societies, the ocean is only a marginal aspect of climate negotiations.

» Medical » When the ocean is dying, the planet too