Earth's Climate Cycles and an Anomaly

Hot or cold, the planet has been home to life and death. Learn about the natural cycles that have driven life and death for millions of years and how they’re different from the climate change of today.

Earth is not still. Inside and out, it moves on different scales of size and time. Its cosmic position, not only in the planetary system, but also in the Milky Way, make it the venue of natural cycles that, from an anthropocentric perspective, inevitably occur without the influence of human actions. 

Among these natural cycles are the climate cycles, which are constant long-term changes in temperature that modify the planet’s atmosphere, surface, and water, and from which has emerged and been extinguished the life of thousands of plants, animals, and other organisms; species that survived, evolved, or that we know only through vestiges, others that left no trace, and others still that we cannot even imagine. But the natural climate cycles of Earth should not be confused with present-day climate change, which has been caused by us humans, is short-term and, more than adding to a cycle, irreversibly catalyzes the end of organisms and ecosystems. What follows is an explanation to avoid confusion. 

Earth’s Natural Climate Cycles

These cycles are repetitive periods in which the planet warms and cools according to the quantity of solar radiation (insolation) that it receives during millions or billions of years. The effects of these changes in temperature have caused five long glacial eras or glaciations with warmer and shorter interglacial periods, started from 2.4 billion years ago within the at least 4.5 billion years of Earth’s age; that is to say, the hot and cold variations have repeated five times, therefore constituting cycles.

The Serbian geophysicist Milutin Milanković used mathematics to understand the relationship between long-term climate change with the Earth’s movements with respect to its distance from the Sun. Thanks to what he discovered, we know how the insolation variations affect Earth’s climate. He identified at least three movements that cause insolation variations: 

Orbital eccentricity: The quantity of solar radiation that Earth receives depending on the shape of its orbit: almost circular or slightly elongated as an ellipse. The transition between quasi-circular and elliptical and vice versa is slow, lasting around 98,000 years, and there is a variation in distance of only 3% between both and of 6% in the solar energy received. The more elliptical the orbit, the more solar radiation the planet receives because this means there is a point where it’s closer to the Sun. Currently, we are moving in an almost circular orbit, so that we receive mostly the same amount of solar energy throughout the year.  

Axial obliquity: The tilt of the rotational axis of the planet along its plane of orbit (its movement around the Sun); that is to say, this axis is also in movement, like a metronome that leans slowly from one side to the other for 41,000 years, therefore, its angle varies in degrees, between 22.1° and 24.5°. There is more solar exposure in the northern hemisphere and less in the southern hemisphere when the axis is inclined toward the Sun and vice versa; that is one hemisphere is warmer than the other depending on the season of the year. Today, the axis is at 23.4 degrees. This implies that the northern hemisphere has the longest day and the shortest night of the year, and the southern hemisphere has the shortest day and the longest night of the year. 

Precession: The rotational axis is tilted, but it also changes direction because the planet is pulled by the force of attraction from the Moon, Jupiter, Saturn, and of course, the Sun. In this spinning top, the tip of the axis forms a circle as it spins tilted during a period of approximately 25,771.5 years. Today’s precession, for example, causes the northern hemisphere to receive more solar radiation during the winter.

When these three movements combine for billions of years, solar exposure on Earth changes with certain tendencies in the polar and equatorial zones. Some regions tend to be temporarily colder than others, while throughout the entire globe there are constant high and low temperatures. 

As a habitat, then, the Earth moves and, thus, mutates within. Ice covers its surface during glaciations, melts during interglaciations, and appears again in a new glaciation. This has occurred with and without human presence since the beginnings of the Earth. Homo sapiens appeared on the planet 200 or 350 thousand years ago (not even a million), and, as a species, we have survived two glacial periods within the geological Quaternary period that began 2.588 million years ago and continues to this day. That is to say, it has been estimated that within the Quaternary geological period there have been four principal glaciations, of which we have survived two. The last one ended 10,000 years ago and was followed by an interglacial period, less icy and warmer, in which we still find ourselves. 

During this last glacial period, the ice was prominent in the north and south of the planet. Some humans managed to resist the low temperatures, particularly those in the south of Ethiopia, who moved to highlands 4,000 meters above sea level in the Bale Mountains. There, despite the cold, the high frequency of rains, and lower oxygen levels, they adapted physically and culturally. According to a study from the Martin-Luther-Universität Halle-Wittenberg in Germany, this area was far from the glacial lands, allowing for Homo sapiens to develop new capacities for survival such as an adaptation to places with lower oxygen levels. They had sufficient water due to the progressive melting of ice, their diet consisted of the fat and meat of mammals like giant rodents and wooly mammoths, for lack of vegetation, and from them obtained the calories necessary for facing these adverse conditions. Due to hunting by humans and climate conditions, some large mammals succumbed: saber toothed cats, land sloths, and mastodons, to name a few. Others more survived, including chimpanzees, servals, bears, kangaroos, and various felines. 

In the same way, during glaciations before the Quaternary, innumerable organisms appeared and disappeared; for example, primitive ones, multicellular ones, amphibians, reptiles, the first mammals, flowering plants. Planet Earth hosts life that adapts or dies out in certain scenarios and atmospheric conditions, that can modify its surroundings and alter ecosystems and its symbiosis with different species, and humans have indeed managed this to a fault. 

Human-induced Climate Change

Although it could seem like an easy explanation, the Earth’s natural cycles that we have just explored are not the main factor in the climate change that we are experiencing today due to the following reasons:

- Current climate change is chronologically associated with the greenhouse effect caused by the burning of fossil fuels starting in the first Industrial Revolution, therefore, its origin is anthropogenic, that is, due to human activities. 

- The oldest record of increased carbon dioxide in the atmosphere within this interglacial period is from 1830, meaning that recent climate change has been occurring for 191 years. During this time, the planet’s climate has increased 1.2° C. In 1880, global surface temperature was -0.16° C, and in 2020, 1.2° C. The World Meteorological Organization estimates that in 2024, it will be at 1.5° C. Thus, the rhythm of change in Earth’s climate is accelerated (measured in decades), not slow as in natural climate cycles (measured in thousands or millions of years).

- The natural cycles are correlated with the increase or decrease in the amount of solar radiation that the planet receives, but in the last 40 years, this has decreased. Therefore, global warming cannot be attributed to an increase in solar radiation.

- We are in an interglacial period: between the last glacial period and the next one that can occur in a few thousand years. Therefore, we should be on track for a colder and colder global climate, not a warmer one, of course considering that interglacial periods are not freezing, but have both warm and cold states.

 

In this context, we humans, born of a combination of effects of temperature and land change, have altered the ecosystems of the planet that hosts us, at this point in an inevitably conscious manner. The excessive carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and water vapor emissions due to the burning of coal, petroleum, and other fuels, deforestation, and other activities, have accelerated not only our physiological adaptation to variations in temperature, but also those of the rest of Earth’s inhabitants. Some species have managed to adapt, but others have fallen abruptly, adding to what has been called the sixth mass extinction in Earth’s history. 

The Circle of Life

In 2017, the University of Washington published a study in which they said that, in the face of climate change and global warming, "many amphibians, mammals, and birds will move to cooler areas outside their normal ranges as long as they find space and a long path between our urban developments and growing cities," but what about fish?

Assuming that not all organisms are equally sensitive to changes in climate, a group of scientists from such a university studied the environmental patterns that would put 3,000 species of fish in oceans and rivers at risk. They found, for example, that freshwater fish at high altitudes in the northern hemisphere will be most at risk when waters are warmer. They will either have to move quickly to other locations to adapt to the changes or will be forced to adapt immediately without moving, which has a high failure rate. Meanwhile, fish living in the tropics are more accustomed to warmer climates, however, they can only endure so long before also needing to move to cooler waters. "Fish will migrate, adapt or die as long as temperatures continue to rise."

The example of fish survival is, therefore, one of many that demonstrate that climate change is rapid and that it does not correspond to a natural cycle of either land temperature or life. The effects of climate change, then, transform the behavior and coexistence of all living organisms, both on land and under water. So far there is no clear record of genetic or morphological changes, but there is a clear record of their life cycles, such as different periods of hibernation, mating or migrations.

If, even out of mere curiosity, we look at geographical models based on satellite images, it is possible to visualize "from the third person" the atmospheric changes on the planet in real time, such as the formation and thawing of the poles, the decrease of water in rivers or seas, or the growth of the hole in the ozone layer. With that perspective, inside the planet, we can witness more closely some of the foreseeable impacts of climate change:

- Sea level rise

- Increase in the number of endangered animal and plant species in danger of extinction

- Decrease in water reserves

- Disappearance of glaciers

- Loss of wetlands

- Increase in poor nutrition and infectious diseases and epidemics 

- Increased mortality and morbidity rates 

- Intensification of heat waves and droughts 

Human intervention catalyzes the natural cycles of the planet, until now to supply itself with more resources. In modern philosophy, the meaning of inhabiting has been rescued as "taking care of" or "looking after", and that of caring as "protecting", "guarding" or leaving something in the essence of the place we inhabit or live in. Since we inhabit the planet, our behavior has an impact on it. "Mortals inhabit to the extent that they save the earth [...]. Salvation not only removes something from danger; to save properly means: to open to something the entrance to its own essence. Saving the earth is more than exploiting it or even strangling it. To save the earth is not to take possession of the earth, it is not to make it our subject, from which only one step leads to limitless exploitation".

This Heideggerian message, in other words, explains that for us mortals to properly inhabit the earth (and the Earth), we let its conditions, seasons, surfaces and elements be as they are, without harming them. And, since we are on this planet, we must learn to inhabit it, take care of it; learn to adapt to it to suit or protect it, and thus have a pleasant life and death on it, which is the only certain goal of humans. "Mortals inhabit to the extent that they conduct their own essence - being capable of death as death - to the use of this capacity, so that it is a good death." In this sense, from any scientific or humanistic perspective, the message is similar: organisms inhabit a planet with cyclical natural characteristics and, if there is awareness, it is possible to avoid or mitigate further damage, to coexist in life and death in the most beneficial way possible for the Earth itself.

 

 

References

Buis, Alan (2020). "Milankovitch (Orbital) Cycles and Their Role in Earth's Climate". Nasa news. https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/

Heidegger, Martin (2007). "Construir, habitar y pensar". En La pregunta por la técnica (y otros textos). Folio: Barcelona. pp. 43-63

Lise Comte, Julian D. Olden. "Climatic vulnerability of the world's freshwater and marine fishes". Nature Climate Change, 2017; DOI: 10.1038/nclimate3382

Nerilie, J. Abram, et. al. (24 August, 2016). “Early onset of industrial-era warming across the oceans and continents”. Nature. https://www.nature.com/articles/nature19082

NSF. “Large Ice-Age Mammal Extinctions: Humans and Climate the Culprits”. NSF News. https://www.nsf.gov/news/news_summ.jsp?cntn_id=122133

Ossendorf, Götz (2019). “Middle Stone Age foragers resided in high elevations of the glaciated Bale Mountains, Ethiopia”. Science; 365 (6453): 583 DOI: 10.1126/science.aaw8942

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