Warming oceans are hotbed for sixth mass extinction

   Every mass extinction, behind it, there seems to be a programmer adjusting the parameters of the earth, adjusting the left and right control of the earth's ecosystem, and carving the temperature and temper of the planet on a long geological scale. In the first five mass extinctions, various species emerged one after another and then gradually disappeared. Trilobites, strange shrimps, dinosaurs, and the mammals of the current year, you sing and I appear.

  However, emissions from fossil fuels change some of the most critical parameters, and the planet's rapid warming threatens a large number of species, including marine life, and their ecosystems. "Science" magazine recently published the research results of Justin Penn and Curtis Deutsch of Princeton University and University of Washington. The team used a physiological-ecological model that took into account the physiological tolerance limits of different marine species and validated using fossil record data to predict the extinction risk and latitudinal distribution of species at the end of the Permian (252 million years ago). Global and local ocean extinction risks under different CO2 emission scenarios were calculated. The quantitative assessment found that if fossil energy use continues to grow rapidly, about a third of all marine animals could become extinct within 300 years, a decline in species on a scale comparable to Earth's past five mass extinctions.

  The new study builds on earlier work by the two authors. They created an Earth-simulation system model detailing the worst oceanic mass extinction in Earth's history at the end of the Permian. The extinction took away more than 90 percent of the species in the ocean, and the model found that as temperatures rose and the metabolism of marine animals increased, gradually warming waters could not hold enough oxygen to keep animals alive. The fossil record, as the support of historical data, also directly and powerfully corroborates the stability and accuracy of this model.

  The study shows that, under a low carbon dioxide emissions scenario, by the end of the century, if global warming is limited to about 1.9 degrees Celsius, species losses will remain similar to current levels. In other words, if the 2°C temperature control target of the Paris Agreement is achieved, the risk of species extinction will be reduced by more than 70%, and the marine species diversity resources accumulated over 50 million years of evolutionary history will be effectively preserved.

  Under the high carbon dioxide emission scenario, the warming reaches about 4.9 degrees Celsius by 2100, and further climbs to 10-18 degrees Celsius in the next three centuries, and the number of species losses increases significantly. Climate change will reshuffle marine ecosystems in unexpected ways, with species losses from both ocean warming and oxygen deprivation rivaling the intensity of current direct impacts of human activities such as overfishing and pollution within a century , and eventually caused a mass extinction comparable to the previous five mass extinctions.

  The study also confirmed that polar species face a higher risk of extinction than lower latitudes. Based on human current greenhouse gas emissions, summer sea ice may disappear completely as early as 2035; and the polar climate amplification effect makes the polar oceans warm more significantly, and the rate of warming in the Arctic may be four times that of the rest of the world. According to the 2020 World Meteorological Organization report, a heat wave in Siberia swept the Far East, with Russia reaching new highs in the region north of the Arctic Circle, and the town of Verkhoyansk even reached an unprecedented 38 degrees Celsius.

  Species extinction rates are lower in lower latitudes, but species richness declines more significantly than in the poles. Lower latitudes were originally richer in biomass and biodiversity, and in addition, species could migrate to higher latitudes, and the proportion of species at risk of extinction was therefore less pronounced and less dramatic than in the poles. However, due to its large base and local demise after migration, the net quantity still has a greater impact.

  If humans cannot quickly and effectively control greenhouse gas emissions, the loss of marine biodiversity will accelerate, and the threat level will even approach several mass extinction events in history.

  Warmer oceans are forcing species to migrate to colder, higher latitudes, while marine species that were originally adapted to polar cold climates have no cooler places to migrate. Occupied by migratory species. The temperature of deep seawater is lower, but the pressure will increase with depth, and the abundance of food will also decrease. Therefore, it is difficult to find suitable habitats to support large populations in the deeper seas. A Rutgers University study argues that ocean warming caused by global warming could lead to significantly fewer high-yielding fish species that can be caught in the future, such as 200 years from now, making it significantly harder for cod-dependent fishermen along the North Atlantic coast.

  To make matters worse, the species' metabolic rate increases as the water temperature rises, requiring more oxygen to perform bodily functions such as respiration. However, the oxygen content in the ocean is only 1/60th of that in the atmosphere, warmer seawater has lower dissolved oxygen content, and seawater circulates more slowly. As global temperatures rise, this concentration may fall even further, increasing the survival of marine life. predicament.

  Deutsch, one of the authors, describes this phenomenon as inflation under the sea: "Imagine inflation, prices go up, and your salary goes down; the oceans provide less oxygen, even though they are more consumed than ever before. need."

  In fact, the relationship between seawater temperature and oxygen content is broad and far-reaching. Surface seawater (that is, seawater with a depth of more than 50 meters) directly contacts the air, and the oxygen content reaches the maximum due to the stirring effect of wind and waves, vertical convection and biological photosynthesis. From below the surface, due to the consumption of oxygen by the oxidative decomposition of organisms and biological debris, the lack of light and the weakening of photosynthesis, the oxygen content continues to decrease with depth, usually reaching a minimum value at 300-1000 meters (this depth varies with sea areas) , such as the continental shelf sea area is greatly affected by the land).

  Because the warmer, oxygen-rich water at the surface is lighter, it is difficult to mix up and down with the deeper, cooler, lower-oxygen water, resulting in stratification of ocean water and the formation of areas of extremely low-oxygen water. In the past 15 years or so, the temperature of seawater has continued to rise, and the deep-sea areas with low oxygen content have been further deoxygenated. The low-oxygen areas in the ocean have expanded rapidly, and the living areas of some marine organisms have been forced to change accordingly. For example, deep-sea divers, tuna and swordfish, who used to forage at depths of 200 meters below the surface, are now often spotted at the surface.

  Eric Galbraith, Professor of Human and Earth System Dynamics at McGill University, said: "This study is based on a well-established model, and its conclusions establish some simple but reliable correlations. What humans are doing now will determine whether we will fall into another mass extinction. ". Rutgers University biologist Malin Pinsky also mentioned in an interview with the media, "If we don't pay attention, human beings will be heading for a rather dire future, and this study is a wake-up call."



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