Studying the impact of carbon emissions and global warming events that have occurred in the late Paleozoic great ice age will help us to better understand the correlation and feedback mechanism within the earth system under the ice chamber climate, so as to more accurately predict the future development trend of global climate, environmental change and biodiversity What are the consequences of global warming? What kind of living environment will life on earth face? Will the current Quaternary ice age conflict with global warming?
In recent years, the global climate problem has become the focus of attention of various countries. So will climate change really have devastating consequences? There are many researches on this problem, but the prediction results are also very different.
In early May, the scientific journal Proceedings of the American Academy of Sciences published an achievement from the cooperation between the Nanjing Institute of Geology and paleontology of the Chinese Academy of Sciences (hereinafter referred to as the Nanjing Institute of Geology and paleontology of the Chinese Academy of Sciences), Nanjing University and the University of California Davis. They believed that there was a short huge amount of carbon emission event during the late Paleozoic ice age about 300 million years ago, It has caused marine hypoxia and significantly reduced marine biodiversity.
The warming caused by carbon emissions has occurred many times in the history of the earth, and the event 300 million years ago attracted the attention of scientists because the earth's environment at that time was very similar to that at present. This achievement is also the first achievement in the world to study global warming in the context of ice age.
The consequences of global warming have emerged
High temperatures in North America, heavy rains in Europe, floods in Asia... Many people may remember that there were many extreme weather events around the world in 2021.
In places beyond the sight of most people, environmental change is also worrying: the accelerated melting of glaciers in Greenland, frequent drought in the Amazon rainforest, large-scale death of coral reefs near Australia, the melting of permafrost in Siberia, and the slowing of Atlantic circulation since 1950.
"According to relevant research reports, at present, the earth we live on may be facing the critical point of climate change." Chen Jitao, a researcher at Nanjing Institute of Geology and paleontology, Chinese Academy of Sciences, told reporters that today's earth is in a Cenozoic ice chamber climate that began 34 million years ago. Under the background of the rapid rise of global climate, the ice level has increased, and the biodiversity of the sea has decreased in the past century.
Global warming was originally a natural phenomenon on the earth. According to the research results of scientists, in the earth's 4.6 billion year history, the temperature changes periodically, and the temperature is relatively high most of the time. At this time, the earth's surface is not covered by continental glaciers or ice sheets. We call these periods the greenhouse period.
If the earth's surface is in a state of extremely low temperature for a long time, resulting in the whole earth's surface covered with ice and snow, we will call these periods the ice chamber period or the great ice period. For example, during the Precambrian ice age, the earth suffered a severe freezing. During this period, the average temperature of the earth may once fall to about minus 50 degrees Celsius, which is known as "Snowball Earth".
But not all ice ages were as cold as snowball Earth. The great glacial period is also divided into glacial period and interglacial period, which occur alternately. At present, the earth is in the interglacial period, and the temperature is relatively higher. However, there are still many glaciers and ice sheets on the earth, mainly concentrated in Greenland and the South Arctic, which is also the most prominent feature of the ice age.
So, what kind of consequences will the current global warming bring?
"Based on the observed data of current environmental change, it is difficult to predict the long-term trend in the future. In order to find the internal relationship between warming and ocean hypoxia and biodiversity change under the background of global ice chamber climate, and more accurately simulate and evaluate the degree of ocean hypoxia, we need to find the answer through the study of ice chamber climate in the history of the earth." Chen Jitao said.
Huge carbon emissions occurred 300 million years ago
In the late Paleozoic era of 360-280 million years, there was also a great ice age on the earth. This great ice age is the longest and largest ice chamber climate on the earth. It is also the only geological period that recorded the transformation of the earth from ice chamber climate to greenhouse climate since the establishment of terrestrial higher plants and terrestrial ecosystem. At that time, the concentration of carbon dioxide and oxygen in the earth's atmosphere was also similar to that in modern times, so this period can be well compared with the ice chamber climate environment in which human beings live today.
Chen Jitao believes that studying the impact of carbon emissions and global warming events that have occurred in the late Paleozoic great ice age will help us to have a deeper understanding of the correlation and feedback mechanism within the earth system under the current ice chamber climate, so as to more accurately predict the future development trend of global climate, environmental change and biodiversity.
In the Carboniferous period 300 million years ago, the earth's continent was different from today. Large tracts of land were concentrated in low latitudes, and China's South China plate was an isolated island in the ocean. Therefore, there are a large number of marine sedimentary strata in the South China plate, which provides a good sample for the study of the marine environment at that time.
The Late Carboniferous sea water in Luoqing, Guizhou has a complete geochemical record.
Researchers have carried out comprehensive research on stratigraphy, paleontology, sedimentology, sedimentary geochemistry, numerical simulation and other disciplines in recent ten years, and found a huge carbon emission event under the ice chamber climate in the Late Carboniferous for the first time.
In order to accurately restore the environmental changes at that time, their sampling accuracy reached the centimeter level. The samples were tested and analyzed by carbon and uranium isotopes and major and trace elements, and then imported into the global carbon cycle model (loscar). The carbon emissions and carbon sources were numerically simulated, and the coupled carbon uranium model was used to calculate the degree of global ocean hypoxia at that time. Finally, the more comprehensive earth system model (cesm) was used for data simulation, Finally, the correlation mechanism between carbon emission and ocean anoxic area in this event is established.
The results show that in the Late Carboniferous (about 304 million years ago) ice chamber climate, about 9 trillion tons of carbon were discharged into the atmosphere within 300000 years, which caused significant global warming at that time. During this period, the sea surface temperature increased by about 4 degrees Celsius, the global ocean anoxic area increased by 18%, expanded from 4% to 22%, and the marine biodiversity decreased significantly in the short term.
"According to our research, a large number of foraminifera, corals and brachiopods in the ocean died at that time. These are benthos. When the ocean is lack of oxygen, the first thing to affect is these organisms with relatively limited mobility." Chen Jitao said.
The study of global warming needs to consider the macro climate background
Researchers speculate that the huge amount of carbon emission in the Late Carboniferous is related to extensive volcanic eruptions. According to the research of other scholars, large-scale volcanic activity occurred in Europe, Australia and other regions at that time.
The Carboniferous is a concentrated coal forming period. A large number of plants are buried underground in the form of solid carbon. Before magma eruption, they may invade these coal seams, resulting in a rapid increase in carbon emission in the short term.
Why does the study of greenhouse gas emissions and global warming need to examine the global climate background? Chen Jitao said that the so-called difference is a thousand miles. Under the ice chamber climate and greenhouse climate, the consequences of global warming are likely to be very different, which must be scientifically demonstrated.
By comparing the carbon emission events in different climatic environments in geological history and the global warming and ocean hypoxia caused by them, the research team proposed for the first time that under the same carbon emission rate, the ocean under the ice chamber climate may have a more serious oxygen deficiency state than the greenhouse climate.
They speculate that there are three main reasons for this: first, during the global warming of the ice chamber climate, the melting of glaciers leads to the reduction of the albedo of the earth's surface, which drives the temperature to rise further; Second, the global warming event weakened the meridional overturned circulation in the northern hemisphere and enhanced the stratification of the oceanic thermocline, thus reducing the mixing depth of the ocean surface water and reducing the oxygen content in the ocean; Third, global warming has led to the melting of glaciers and the exposure and weathering of large areas of land, causing phosphorus and other nutrients to enter the ocean, promoting primary productivity and consuming a large amount of oxygen in seawater.
The amount of 9 trillion tons of carbon discharged into the atmosphere in 300000 years sounds amazing, but it is far less than the greenhouse gas emissions caused by human activities in recent 200 years.
Taking 2018 as an example, the global carbon dioxide emission is 34 billion tons, which is converted into about 9.3 billion tons of solid carbon, while the huge carbon emission in the Late Carboniferous is about 30 million tons per year, hundreds of times that of the latter.
According to the observation of the World Meteorological Organization, the concentration of carbon dioxide in the global atmosphere has exceeded 410ppm (410 parts per million) in 2019, a new high in the past 800000 years. In March 2022, this figure rose to 418.81 ppm (418.81 parts per million).
So, will the current global warming overturn the periodic changes of the earth? According to the research of scientists, if the current carbon emission rate is not limited, the periodic climate change in the history of the earth may be broken, and the earth may enter the state of greenhouse climate.