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Unless we act quickly to limit global warming, nearly all marine species will be at high or critical risk of extinction by the end of the century. Also, there is still time to act to avoid these gloomy prospects. At least that is what a study published in the journal Nature Climate Change reports on August 22.

This is the kind of news that unfortunately surprises us less and less. We all know that the living world is very hard hit by pollution, climate change, deforestation and other practices of overexploitation of natural resources. However, new studies reveal that if greenhouse gas emissions continue at the current rate, no less than 90% of marine species will be at risk of extinction by the end of the century.

In their study, the international team of researchers took into account some twenty-five thousand species located in the upper ocean and how they are likely to react to the continued rise in temperatures as well as increasing acidification. waters. Indeed, it should be remembered that in addition to causing an accumulation of heat in the climate system, part of the atmospheric carbon dioxide (CO2) dissolves in the ocean and lowers its pH.

Towards a carnage of marine life in the event of inaction or insufficient action
The results show that with global warming of 3°C to 5°C, corresponding to an absence of regulation of greenhouse gas emissions, 90% of marine life forms would be threatened with extinction. The good news is that with global warming kept at 2°C in line with the objectives of the Paris climate agreement, the risk of extinction would be greatly reduced for most of the species studied. This scenario of course implies a rapid and deep decrease in our emissions with a net zero reached around the middle of the century.

The life forms most at risk are often those experiencing other stresses such as overfishing. It goes without saying that with such a collapse of marine life, human societies would be very hard hit, especially with regard to populations and economies that depend very directly on fisheries resources. For these low-income countries often located in the deep south, the issue of food insecurity is therefore a serious one.

Note that if we fail to keep the climate at a level consistent with the goals of the Paris Agreement, we would be heading for the greatest extinction of species ever known on Earth since the terrible episode of the Permian-Triassic boundary that decimated over 95% of marine life 252 million years ago. “Our climate risk assessment can help prioritize vulnerable species and ecosystems for marine conservation and fisheries management efforts,” the study notes in its executive summary.

By ingeniously taking advantage of elephant seals, a study has shed light on the mechanisms involved in the dynamics of the Blob, this exceptional marine heat wave that occurred a few years ago in the northeast Pacific. The results were published in the Journal of Geophysical Research: Oceans on July 4.

The marine heat wave that affected the northeast Pacific between 2013 and 2016 was the most intense ever reported since the beginning of observations, with anomalies sometimes exceeding 6°C. Named The Blob in reference to a nanar from the 1950s, it has fueled a large body of studies, especially since several aftershocks have occurred since then, including a notable one between 2019 and 2021.

Elephant seals to examine The Blob

Thanks to sensors placed on a group of northern elephant seals, a team of researchers was able to record the phenomenon from below from 2014 to 2017. Indeed, if the monitoring of temperature anomalies on the surface of the sea is easy thing with satellite instruments, the situation quickly becomes complicated for anomalies located below the surface. However, they play a strong role in terms of the persistence and risk of a resurgence of the heat wave.

“Elephant seals collect data in places different from existing oceanographic platforms,” reports Christopher Edwards, lead author of the study. “This is an underutilized dataset that can tell us about important oceanographic processes and help biologists understand the ecology of northern elephant seals.”

An understanding of the phenomenon that is being refined

The most valuable measurements were collected during the migratory phases, when the animals dive several hundred meters deep and travel long distances. They revealed larger heat anomalies than previously estimated, with an extended thermal excess at least up to a thousand meters deep. The latter was also largely maintained during 2017, at the very time when the Blob was disappearing on the surface.

“These temperature anomalies are so deep that they are unlikely to result from mixing from the surface,” explains the researcher. “A reasonable mechanism is that the exceptionally warm waters were transported north from the south. What we don’t yet know is whether this northward transport is directly related to surface warming. Surface changes may have transiently altered deeper currents to pull southerly waters northward.”

What is certain, however, is that in a context of global warming, marine heat waves will become more frequent, more intense and will affect larger areas. As the latest IPCC report indicates, these are trends that have already begun. For example, since the 1980s, the number of marine heat waves has doubled worldwide.

“The more information we can collect, the better off we will be in terms of understanding what is happening and dealing with challenges,” the lead author points out. “While elephant seals have been used to study the physical oceanography of polar regions for some time, this is one of the first studies to use the data collected to answer oceanographic questions in temperate regions, such as the North Pacific Ocean.