5.9 Intellectual The Intellectual
As greenhouse gas emissions continue to warm the oceans, marine biodiversity could be lost over the next few centuries, reaching levels not seen since the extinction of the dinosaurs| Image source: pixabay.com
Introduction
The warming and oxygen-starved waters test the viability of marine species and drive them to the poles, triggering an extinction crisis for marine species, especially polar species.
In the study, published in The journal Science in April, researchers simulated the relationship between end-Permian extinction risk and climate change and validated it with fossil record data; the study migrated the model to the current environment, quantitatively analyzing the future extinction risk of global and local marine organisms under different carbon dioxide emission scenarios.
The results show that if humans fail to control greenhouse gas emissions quickly and effectively, the rate of loss of marine biodiversity will accelerate, and the threat level will even approach several mass extinction events in history.
Written by | Ding Yutian
Editor-in-charge | Feng Hao
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Every time there is a mass extinction, behind it is like a programmer tuning the earth, turning left and right to the earth's ecosystem, shaking here and there, firing a fire over there, dropping two stones from time to time, carving the temperature and temper of the planet under a long geological scale. In the first five mass extinctions, various species have emerged and gradually withdrawn, trilobites, strange shrimp, dinosaurs, and mammals that are now in their prime.
Figure 1 Ancient Ocean Behemoth - Canglong | Source: Network
However, emissions from fossil fuels have altered some of the most critical parameters, and the planet's rapid warming threatens a large number of species, including marine life, and their ecosystems. On April 29, Science magazine published the findings of Justin Penn and Curtis Deutsch from Princeton University and the University of Washington [1]. The team quantified the risk of global and local marine extinction under different carbon dioxide emission scenarios using physiological and ecological models that took into account the physiological tolerance limits of different marine species, validated using fossil record data, and were able to predict species extinction risk and species latitude distribution at the end of the Permian Period (252 million years ago). Quantitative assessments have found that if fossil energy use continues to grow rapidly, about a third of marine animals could become extinct within 300 years, a scale of species loss comparable to Earth's past five mass extinctions.
The new study builds on the authors' earlier work [2]. They created an Earth simulation system model that details the worst ocean mass extinction in Earth's history at the end of the Permian. The extinction wiped away more than 90 percent of species in the ocean, and the model found that as temperatures rose and marine animal metabolism accelerated, the gradually warming seawater could not hold enough oxygen to sustain the animals. The fossil record, as a support for historical data, also directly and strongly supports the stability and accuracy of this model [3].
Figure 2 Left: Intensity of extinction in the fossil record of marine animals over the past 542 million years. The horizontal axis is the number of occurrences in the past, the left vertical axis is the extinction ratio, and the right vertical axis is the normal distribution statistical proportion. Five horizontal lines represent the proportion of extinctions for each mass extinction event; right: the global extinction risk predicted by the model. The vertical axis is the extinction ratio, and the horizontal axis is the difference in the rise of the Earth's average temperature| source[1]
Figure 3 predicts the risk of global demise. The vertical axis is the extinction ratio, the horizontal axis is the difference in the earth's average temperature rise| source [1] Extinction refers to the complete disappearance of a species from the earth; extirpation refers to the fact that a particular species is difficult to find in a specific geographical area, possibly because it has migrated to another region. [4]
The study shows that under a low CARBON dioxide emission scenario, species losses will remain similar to the current state by the end of the century if global warming increases are controlled within about 1.9 degrees Celsius (Figures 2 and 3, blue lines). In other words, if the 2-degree Celsius temperature control target of the Paris Agreement is achieved, the risk of species extinction will be reduced by more than 70%, and the resources of marine species diversity accumulated over 50 million years of evolutionary history will be effectively preserved.
In the high-co2 emission scenario, warming will reach about 4.9 degrees Celsius by 2100 and climb further to 10-18 degrees Celsius over the next three centuries, significantly increasing the number of species lost (Figures 2 and 3, red lines). Climate change will reshuffle marine ecosystems in unexpected ways, with species losses caused by both warming and hypoxia in the oceans rivaling the intensity of the immediate effects of current human activities (such as overfishing and pollution) within a century, and ultimately causing mass extinctions on a scale comparable to the previous five mass extinctions.
Figure 4 Relationship between marine species extinction risk and latitude| source[1]
The study also confirmed that polar species at lower latitudes face a higher risk of extinction. According to current human greenhouse gas emissions, summer sea ice may disappear completely by 2035 at the earliest, and the polar climate amplification effect makes the polar ocean warming more significant, and the Arctic may be warming at four times the rest of the world [5]. According to the 2020 World Meteorological Organization report, the Siberian heat wave swept across the Far East, Russia hit new highs in the region north of the Arctic Circle, and the town of Verkhoyonsk reached an unprecedented 38 degrees Celsius [6].
Species extinction rates are lower in the lower latitudes, but species richness declines more significantly than in the polar regions. In addition, species can migrate to higher latitudes, and the proportion of species with the potential for extinction is therefore less pronounced and more intense than in the polar regions. However, due to its large base and the local demise after migration, the net number still has a greater impact.
Figure 5 A scrawny polar bear | on a crumbling ice floes Source: Kerstin Langenberger Photography@facebook
Warmer oceans force species to migrate to colder, higher-latitude seas, and marine species that were originally adapted to the colder climates of the polar regions have no colder places to migrate, and parts of the polar niche are occupied by migratory species that avoid warming from low latitudes. Deep seawater is cooler, but the pressure increases with depth and food abundance decreases, making it difficult to find suitable habitats deeper in the ocean to support large populations. A Rutgers university study [7] argues that warming of the oceans due to global warming will lead to a significant reduction in the number of high-yielding fish species that can be caught in the future, for example, after 200 years, fishermen who rely on cod on the North Atlantic coast will have a significant increase in the difficulty of catching.
To make matters worse, species metabolic rate increases as water temperature rises, so more oxygen is needed to complete bodily functions such as breathing. However, the oxygen content in the ocean is only one-sixtieth of that in the atmosphere, and the dissolved oxygen content of warm seawater is even lower, and the seawater circulation is more slow, and this concentration may even decline further as the global temperature rises, increasing the survival dilemma of marine life.
Deutsch, one of the authors, describes this phenomenon as inflation below the surface of the sea: "Imagine inflation, prices rising, and your salary falling; the oceans provide less oxygen, even though they are needed more than ever." ”[8]
In fact, the relationship between seawater temperature and oxygen content is extensive and far-reaching. Surface seawater (i.e. seawater with a water depth of more than 50 meters) is in direct contact with the air, and the oxygen content reaches its maximum due to the agitation of wind and waves, vertical convection and photosynthesis of organisms. Below the surface, due to the oxidative decomposition of organisms and biological debris, oxygen consumption, insufficient light, weakened photosynthesis, and oxygen content continues to decrease with depth, usually reaching a minimum value at 300–1000 m [9] (this depth varies with sea area, such as the continental shelf sea area is greatly affected by land).
Because the surface of warm oxygen-rich water is lighter, it is difficult to mix up and down with colder, oxygen-containing water bodies in the deeper layers, resulting in the stratification of marine water bodies and the formation of areas of water bodies with extremely low oxygen content. In the past 15 years or so, the sea temperature has continued to rise, the deep sea area, which originally has a low oxygen content, has been further deoxidized, the low-oxygen area in the ocean has expanded rapidly, and the living area of some marine organisms has been forced to change accordingly. For example, deep-sea divers, tuna and swordfish, who originally foraged at depths 200 meters below the surface, are now often found floating out of the sea [10].
Eric Galbraith, a professor of human and Earth system dynamics at McGill University, said: "The study is based on a well-established model whose conclusions establish some simple but reliable correlations. What humanity does today will determine whether we will fall into mass extinction again" [8]. Rutgers University biologist Malin Pinsky also mentioned in an interview with the media that "if we are careless, humanity will move towards a rather terrible future, and this study is a wake-up call" [11].
This isn't the first time the alarm bells have sounded.
In the 1980s, a heat wave swept across the Pacific and a small silver fish called the Galapagos damsel became extinct in the waters of Central and South America [12]. In late February 2017, an extreme heat off the coast of Brazil in Uruguay led to massive deaths of shellfish and fish, a significant reduction in local catches, and an algae outbreak caused by a heat wave forced the authorities to close beaches urgently [13]. In July 2021, the sea surface in northern Japan and southeastern Hokkaido was 2 to 4 degrees Celsius warmer than normal in previous years, and Hokkaido fishermen, as Japan's largest fishing ground, claimed that saury catches were 90% less than 10 years ago, that squid was 80% less and salmon was 60% less .[14]
Researchers have tracked the extinction risk of 119 species of north-east Atlantic and 72 Mediterranean sharks and rays. From 1980 to 2015, the proportion of threatened species rose from 29% to 41% in the northeast Atlantic, and from 47% to 65% in the Mediterranean, with researchers citing climate change as one of the key factors in biodiversity degradation [15]. The latest assessment by the United Nations Intergovernmental Panel on Climate Change (IPCC) includes a section entitled "The Great Barrier Reef Crisis" [16], which reports that the dying reef-building corals are a prominent example of species being pushed beyond the temperature limit, with coral bleaching becoming increasingly frequent and severe.
Figure 6 IUCN estimates of the current global risk of extinction of marine life and its drivers. The horizontal axis is the risk type, and the vertical axis is the number of affected species. Climate change is only part of the threat to marine life, currently affecting about 45% of endangered marine species, but it is still lower overall than overfishing, maritime transport, coastal urban development and pollution, ranking fifth among risk factors| source[1]
The impact of climate change on the oceans is never monolithic, it is more like a compound effect, warming of the sea, ocean acidification, sea level rise, melting ice, changes in ocean currents, lack of oxygen in seawater, collapse of the food chain, etc. [17]; coupled with human activities such as overfishing, maritime transport, development and pollution of coastal cities, it may be associated with climate change, causing cascading effects.
Corresponding to the multifaceted threat of human activities to marine life, there are many tools in the toolbox to alleviate the pressure of marine life extinction: reducing the burning of fossil fuels and slowing greenhouse gas emissions; promoting international negotiations to explore the construction of super-large high seas marine protected areas; strengthening illegal, unreported and unregulated fisheries management in support of countries with weak resource management capacity; avoiding unplanned overfishing, reducing harmful fisheries subsidies; avoiding the use of refractory and disposable nets, Reduce unnecessary species sacrifice due to mesh entanglement and bycatch.
The authors initially gave their study a simple title, The Risk of Extinction of Marine Life From Warming. Before submitting, they finally decided to add a word, a very important word - "avoid". In an interview with the media, Deutsch said they wanted to emphasize that the focus of the study was not on the panic and anxiety that an imminent ecological crisis was imminent, but rather that while the results described were grim, the worst outcomes could still be avoided through positive action [3].
Acknowledgements: Thanks to Bai Ming, Chen Yingjie, Jiang Zhongjing, and Ren Guozhi for their suggestions for this article.
Author Bio
Yutian Ding, Ph.D. candidate, Department of Science in New Fields, University of Tokyo.
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References: (Swipe up and down to browse)
1. L., P. J., & Curtis, D. (2022). Avoiding ocean mass extinction from climate warming. Science, 376(6592), 524–526. https://doi.org/10.1126/science.abe9039
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Plate editor| Ginger Duck