If average temperatures on the ground have been increasing since the beginning of the pre-industrial era, this is also the case in the oceans, but at a slower rate, points out Anne de Vernal. It should be remembered here that the oceans occupy 70% of the Earth’s surface. Without them, global warming would be much greater since the oceans have so far absorbed 90% of the excess heat caused by climate change. They also absorb almost 30% of the CO2 emitted each year.
“The ocean is thus a reservoir of heat which accumulates energy,” explains Ms. de Vernal. However, the reservoir homogenization times are very long, of the order of a thousand years. » Concretely, this means that the current warming of the oceans is irreversible. In the event that humanity stops emitting greenhouse gases (GHG) today, the time it will take for the oceans to cool down will take thousands of years. Conversely, not reducing our emissions contributes to accelerating the warming of the oceans, which we now observe at depths of up to 2000 meters.
This is the title of an analysis published by researchers from the Ocean platform
This phenomenon can be observed almost everywhere on the planet. In a recent report, scientists from the Maurice Lamontagne Institute, located in Mont-Joli, in the Lower St. Lawrence, reported that oxygen levels of about 10% are currently being observed in the deep waters off Rimouski. Waters considered low in oxygen have a saturation rate of 30%. At 20%, the level can be fatal for many aquatic species. More tolerant species, such as halibut and northern shrimp, cannot survive at oxygen levels below 10 to 15%. In short, the deoxygenation of the oceans associated with water acidification is a concern for the scientific community.
One of the consequences of climate change is the rise in sea levels, which is also irreversible. Two phenomena are at the origin of this increase, specifies Anne de Vernal. First there is the thermal expansion of the ocean. “The volume of water increases with temperature. A direct effect of warming is therefore an increase in the volume of ocean water. » Sea level has been rising 1.3 mm per year since 2005 due to thermal expansion. The other, more well-known explanation is the melting of the ice caps, “notably that of Greenland which loses around 268 gigatons of ice each year, according to satellite measurements since 2002,” adds Ms. de Vernal. The melting of ice caps has caused ocean levels to rise by 2.2 mm per year since 2002. Over the past 30 years, ocean levels have risen by 103.3 mm or 10 cm on average, according to official data. An essential reference on this subject remains the Sea Level Change site, produced by NASA, which contains a multitude of data on sea level rise.
Ocean warming, deoxygenation, and acidification are not without consequences for marine biodiversity, Anne de Vernal points out. “The latest estimates from the United Nations Educational, Scientific and Cultural Organization warn that more than half of marine species could be on the brink of extinction by 2100. With a current temperature rise of 1.1°C, it is estimated that 60% of the planet’s marine ecosystems have already been degraded or are being used unsustainably,” the UN states in a recent publication recommended by the researcher. For example, we know that 70 to 90% of coral reefs will disappear with warming of at least 1.5°C by the end of the century, a proportion that will increase to 99% with warming of at least 2°C. To better understand coral bleaching, she suggests reading about it on the Woods Hole Oceanographic Institution website.