Is the Quaternary Ice Age encountering global warming the human living environment cold or hot?

Is the Quaternary Ice Age encountering global warming the human living environment cold or hot?

◎ Intern reporter Sun Mingyuan

Focus on global warming (2)

The Earth has become our home because of its habitable environment, but in reality, it is not a docile planet, but just in the last few hundred thousand years just in a suitable state for human survival. In the history of the earth, there have been tens of millions of years of severe cold, as well as heat and rains that have lasted for millions of years. Earth's temperature has been changing for long periods of time over billions of years. Therefore, measuring global warming needs to be done from a human perspective. We are concerned about global warming because it is closely related to the survival and development of mankind.

Climate change at the Earth scale

Humanity is now in the midst of a great ice age

Wu Huiting, a lecturer in geology at China University of Mining and Technology (Beijing), introduced that when discussing earth's climate change, "scale" is a very important concept. Geologists refer to the period in Earth's history when the atmosphere and the long-term low temperatures on the surface led to the massive expansion of polar and mountain ice sheets, and even covered the entire continent, as the Great Ice Age. The timescale for measuring the Great Ice Age is millions of years. Since the formation of the Earth, there have been at least 5 great ice ages, each lasting tens of millions of years. At the height of the Great Ice Age, the Arctic and Antarctic ice sheets covered a very wide area, exceeding 30% of the total surface area. In contrast, during the Great Ice Age, the Earth was in what geologists call the Greenhouse Period, when there were no continental glaciers (including the North and South Poles) on earth.

Scientists estimate that more than 85 percent of Earth's 4.6 billion-year history has been during the greenhouse period. From this perspective, the Great Ice Age was just an "interlude" of the greenhouse period, but as mentioned earlier, the term "interlude" is for billions of time scales.

Wu Huiting, for example, said that the cold of the Ice Age is particularly typical of the "Snowball Incident". The "Snowball Event" refers to the fact that between 750 million and 580 million years ago, the Earth experienced a Great Ice Age that lasted more than 10 million years, during which some scientists speculate that the average temperature on the Earth reached minus 50 ° C at one point, and the entire Earth was frozen. During the "Snowball Event" period, only a small number of creatures living near volcanoes or in ungalized seas survived.

Although not every Ice Age is as cold as it was when the Snowball Event occurred, and each Ice Age also has its own evolutionary cycle, which is not always in its peak, the length of the EvolutionAry Cycle and the magnitude of the fluctuations of the Earth's climate can already be seen. In fact, we humans are in the midst of a great ice age today, the Quaternary Ice Age, and the ice sheets of Antarctica and Greenland are symbols of this ice age. For most of Earth's history, during the greenhouse period, the average temperature was much higher than it was at the moment of the Great Ice Age. And lower average temperatures are not uncommon during the Great Ice Age of history.

When we reduce the scale of observation from million years to 100,000 years, we can observe smaller glacial and interglacial periods during the Great Ice Age. The Great Ice Age itself consists of many shorter cycles, of which the relatively cold period is called the Ice Age and the relatively warm period is the Interglacial Period. Humans are currently living during an interglacial period that began about 11,000 years ago, and the average annual temperature is now 15°C higher than the peak of the Quaternary Ice Age about 18,000 years ago. Scientists expect that the next ice age will arrive in about 90,000 years, and the "frozen" world will come again.

Climate change cycles are influenced by multiple factors

Changes in the Earth's orbit, plate movement, etc. all act in it

As a scholar of paleontology, Wu Huiting added that climate change in geological history has a major impact on biological evolution. For example, the global oxygenation event more than 2 billion years ago led to the emergence of eukaryotes, and the super-large volcanic eruption event 250 million years ago increased the global temperature, hypoxia and acidification of seawater, resulting in a large number of extinctions on the earth at that time, subverting the face of the global marine ecosystem.

Why is there a million-year cycle of the Great Ice Age-Greenhouse Period on Earth, and why is there a 100,000-year cycle of ice age-interglacial period inside the Ice Age? To explain these problems, scientists have proposed a large number of hypotheses, the most influential of which is the "Milankovic cycle" named after the Yugoslav geophysicist and astronomer Milanković. Milankovich speculated that the formation of glacial and interglacial periods is related to changes in the Earth's orbit, depending on eccentricity, tilt of the Earth's axis, the position of the summer solstice in the Northern Hemisphere and other factors. The hypothesis proposed by Milankovich, supported by subsequent geological evidence, has become a generally accepted theory in the scientific community. As for the causes of the Formation of the Great Ice Age, possible influencing factors proposed by the scientific community include plate motion and the position of the solar system in the Milky Way. Taking the "Snowball Event" as an example, scientists speculate that the cause of this Ice Age is that the rock weathering brought about by plate movement consumes too much carbon dioxide, and the reason for the end is that thousands of years of volcanic eruptions have released and accumulated a large amount of carbon dioxide.

Compared with these long cycles and drastic changes in the history of the earth, the climate change experienced by human beings in the thousands of years of civilization is insignificant. Compared with celestial bodies and plate movements, the impact of human activities on Earth's climate also looks like a drop in the ocean. So why is global warming important to us? Why are the views of "skeptics" and "conspiracy theorists" undesirable? In the final analysis, to understand these problems, we must further narrow the scale of observation and observe from the perspective of human society.

Global warming at the human scale

Our activities have altered the normal trajectory of climate change

Over the long term, the dominance of celestial bodies and plate movements over Earth's climate change is absolute, and surface organisms are like floating dust compared to their power. However, tenacious Life on Earth has developed the ability to influence the climate in its own evolution. In the midst of climate change, measured on a million-year scale, the role of living things as a whole may only be said to be about participation. But for these creatures themselves, which live from a few minutes to a few hundred years, a little bit of climate change can be said to be life-threatening — and humans are no exception.

The staff of the Anhui Provincial Geological Museum and the Institute of Paleontological Fossil Sciences introduced the position of human beings in the history of climate change to the science and technology daily reporter: In the history of the earth, there are three types of organisms that affect climate change by changing the carbon cycle. The first to emerge are photosynthetic organisms (algae), which have the ability to convert carbon dioxide into oxygen, fixing more than 90% of carbon dioxide in the original atmosphere. What follows is a decomposer (soil microbiome), which breaks down plant fibers and puts carbon dioxide back into the atmosphere, allowing the carbon cycle to be established. It is precisely because of the successive appearance of these two that the ice chamber effect once appeared on the earth, and then it was dissolved.

The last of the three, humans, have only gained the ability to influence the climate in the last 200 years — humans who entered the industrial age have dug up fossil fuels underground and released carbon dioxide through large-scale consumption. Human activity has broken the carbon cycle that the Earth's organisms have maintained for hundreds of millions of years, and within 200 years, the release of the fossil carbon pool in nature that would have taken tens of millions or even hundreds of millions of years to complete – this is the origin of "global warming".

In the scientific community, the issue of global warming has also experienced a century of controversy. It is difficult for scientists to determine whether human activities have the ability to have even a small impact on the Earth's climate, and whether current climate change is a normal expression of nature's cycles. By the end of the 20th century, however, there was growing evidence that the impact of human activities on the climate did exist, and that the impact had been large enough to alter the trajectory of normal change, and global warming became the consensus of the scientific and political circles.

"We found that the number of biological species on Earth and the rate and magnitude of climate change at the moment far exceed the most tragic and serious mass extinction events that have occurred in geological history." Wu Huiting said, "At present, scientists are deeply studying the relationship between the origin and evolution of early life on Earth and climate change, and using big data to analyze trends. ”

Some studies in recent years have shown that cattle and sheep burping, farting to release methane, wild boar foraging and destroying the soil will increase carbon emissions. Among them, the issue of greenhouse gas emissions from livestock has been paid attention to by international organizations and governments, and the carbon emission of wild boar activities is a new research result published by scientists in 2021. However, compared with these animal activities, human consumption of fossil energy has always been the dominant factor in greenhouse gas emissions.

Geologists pay little attention to research problems at scales below 100,000 years. For the Earth, which has existed for 4.6 billion years, a million years is nothing more than a whisker. But for human society itself, climate upheavals on a million-year scale are out of reach, and there is no need to worry about the next ice age that will come in 90,000 years, but the survival and development of the next thousand or even a hundred years is imminent. It is on the timescale that belongs to human beings that human-induced global warming is of crucial significance. Protecting the environment, striving to maintain a suitable climate, and striving to achieve carbon peaking and carbon neutrality are ultimately about protecting human beings themselves.

Source: Science and Technology Daily