10 cases of anthropogenic fluctuations in the Earth's climate

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

For a long time, the Earth's climate has fluctuated for ten different reasons, including orbital wobbles, tectonic shifts, evolutionary changes, and other factors. They plunged the planet either in ice ages or in tropical heat. How do they relate to contemporary anthropogenic climate change?

Historically, the Earth has managed to be a snowball and a greenhouse. And if the climate changed before the appearance of man, then how do we know that it is we who are to blame for the sharp warming that we observe today?

Partly because we can draw a clear causal relationship between anthropogenic carbon dioxide emissions and a 1.28 degree Celsius rise in global temperature (which, incidentally, continues) over the pre-industrial era. Carbon dioxide molecules absorb infrared radiation, so as their amount in the atmosphere increases, they retain more heat, which evaporates from the planet's surface.

At the same time, paleoclimatologists have made great strides in understanding the processes that led to climate change in the past. Here are ten cases of natural climate change - compared to the current situation.

Solar cycles

Scale:cooling by 0, 1-0, 3 degrees Celsius

Timing:periodic drops in solar activity lasting from 30 to 160 years, separated by several centuries

Every 11 years, the solar magnetic field changes, and with it comes 11-year cycles of brightening and dimming. But these fluctuations are small and affect the Earth's climate only insignificantly.

Much more important are the "large solar minima", ten-year periods of decreased solar activity that have occurred 25 times over the past 11,000 years. A recent example, the Maunder minimum, fell between 1645 and 1715 and caused solar energy to drop 0.04% -0.08% below the current average. For a long time, scientists believed that the Maunder minimum could cause the "Little Ice Age", a cold snap that lasted from the 15th to the 19th century. But it has since emerged that it was too brief and happened at the wrong time. The cold snap was most likely caused by volcanic activity.

For the past half century, the Sun has been slightly dimming, and the Earth is warming up, and it is impossible to associate global warming with a celestial body.

Volcanic sulfur

Scale:cooling by 0, 6 - 2 degrees Celsius

Timing:from 1 to 20 years old

In 539 or 540 A. D. e. there was such a powerful eruption of the volcano Ilopango in El Salvador that its plume reached the stratosphere. Subsequently, cold summers, drought, famine and plague ravaged settlements around the world.

Eruptions on the scale of Ilopango throw reflective droplets of sulfuric acid into the stratosphere, which screen sunlight and cool the climate. As a result, sea ice builds up, more sunlight is reflected back into space and the global cooling is intensified and prolonged.

Following the eruption of Ilopango, the global temperature dropped by 2 degrees over 20 years. Already in our era, the eruption of Mount Pinatubo in the Philippines in 1991 cooled the global climate by 0.6 degrees for a period of 15 months.

Volcanic sulfur in the stratosphere can be devastating, but on the scale of Earth's history, its effect is tiny and also transient.

Short-term climate fluctuations

Scale:up to 0, 15 degrees Celsius

Timing: from 2 to 7 years

In addition to seasonal weather conditions, there are other short-term cycles that also affect rainfall and temperature. The most significant of these, the El Niño or Southern Oscillation, is a periodic change in circulation in the tropical Pacific Ocean over a period of two to seven years that affects rainfall in North America. The North Atlantic Oscillation and the Indian Ocean Dipole have a strong regional impact. Both interact with El Niño.

The interrelation of these cycles has long hindered the ability to prove that anthropogenic change is statistically significant, and not just another leap in natural variability. But since then, anthropogenic climate change has stepped far beyond natural weather variability and seasonal temperatures. The 2017 US National Climate Assessment concluded that "there is no conclusive evidence from the observational data that could explain the observed climate change by natural cycles."

Orbital vibrations

Scale: approximately 6 degrees Celsius in the last 100,000 year cycle; varies with geological time

Timing: regular, overlapping cycles of 23,000, 41,000, 100,000, 405,000 and 2,400,000 years

The Earth's orbit fluctuates when the Sun, Moon and other planets change their relative positions. Due to these cyclical fluctuations, the so-called Milankovitch cycles, the amount of sunlight fluctuates at mid-latitudes by 25%, and the climate changes. These cycles have operated throughout history, creating alternating layers of sediment that can be seen in rocks and excavations.

During the Pleistocene era, which ended about 11,700 years ago, Milankovitch cycles sent the planet into one of its ice ages. When the Earth's orbit shift made northern summers warmer than average, massive ice sheets in North America, Europe, and Asia melted; when the orbit shifted again and the summers became colder again, these shields grew back. As the warm ocean dissolves less carbon dioxide, the atmospheric content increased and fell in unison with the orbital oscillations, amplifying their effect.

Today, the Earth is approaching another minimum of northern sunlight, so without anthropogenic carbon dioxide emissions, we would enter a new ice age in the next 1,500 years or so.

Faint young sun

Scale: no total temperature effect

Timing: permanent

Despite short-term fluctuations, the brightness of the sun as a whole increases by 0.009% per million years, and since the birth of the solar system 4.5 billion years ago, it has increased by 48%.

Scientists believe that from the weakness of the young sun, it should follow that the Earth remained frozen for the entire first half of its existence. At the same time, paradoxically, geologists have discovered rocks aged 3.4 billion years, formed in water with waves. The unexpectedly warm climate of the early Earth appears to be due to some combination of factors: less land erosion, clearer skies, shorter days, and a special composition of the atmosphere before Earth got an oxygen-rich atmosphere.

Favorable conditions in the second half of the Earth's existence, despite the increase in the brightness of the sun, do not lead to a paradox: the Earth's weathering thermostat counteracts the effects of additional sunlight, stabilizing the Earth.

Carbon dioxide and weathering thermostat

Scale: counteracts other changes

Timing: 100,000 years or longer

The main regulator of the Earth's climate has long been the level of carbon dioxide in the atmosphere, since carbon dioxide is a persistent greenhouse gas that blocks heat, preventing it from rising from the planet's surface.

Volcanoes, metamorphic rocks and carbon oxidation in eroded sediments all emit carbon dioxide into the sky, and chemical reactions with silicate rocks remove carbon dioxide from the atmosphere, forming limestone. The balance between these processes works like a thermostat, because when the climate warms up, chemical reactions are more effective at removing carbon dioxide, thus slowing the warming down. When the climate cools down, the efficiency of the reactions, on the contrary, decreases, facilitating the cooling. Consequently, over a long period of time, the Earth's climate remained relatively stable, providing a habitable environment. In particular, average carbon dioxide levels have been steadily declining as a result of the increasing brightness of the Sun.

However, it takes hundreds of millions of years for the weathering thermostat to react to the surge of carbon dioxide in the atmosphere. Earth's oceans absorb and remove excess carbon faster, but even this process takes millennia - and can be halted, with the risk of ocean acidification. Each year, burning fossil fuels emits about 100 times more carbon dioxide than volcanoes erupt - the oceans and weathering fail - so the climate heats up and the oceans acidify.

Tectonic shifts

Scale: approximately 30 degrees Celsius over the past 500 million years

Timing: millions of years

The movement of the land masses of the earth's crust can slowly move the weathering thermostat to a new position.

For the past 50 million years, the planet has been cooling, tectonic plate collisions pushing chemically reactive rocks like basalt and volcanic ash into the warm humid tropics, increasing the rate of reactions that attract carbon dioxide from the sky. In addition, over the past 20 million years, with the rise of the Himalayas, Andes, Alps and other mountains, the rate of erosion has more than doubled, leading to an acceleration of weathering. Another factor that accelerated the cooling trend was the separation of South America and Tasmania from Antarctica 35.7 million years ago. A new ocean current has formed around Antarctica, and it has intensified the circulation of water and plankton, which consumes carbon dioxide. As a result, Antarctica's ice sheets have grown significantly.

Earlier, during the Jurassic and Cretaceous periods, dinosaurs roamed Antarctica, because without these mountain ranges, the increased volcanic activity kept carbon dioxide at levels of about 1,000 parts per million (up from 415 today). The average temperature in this ice-free world was 5-9 degrees Celsius higher than it is now, and the sea level was 75 meters higher.

Asteroid Falls (Chikshulub)

Scale: first cooling by about 20 degrees Celsius, then warming by 5 degrees Celsius

Timing: centuries of cooling, 100,000 years of warming

The database of asteroid impacts on the Earth contains 190 craters. None of them had a noticeable effect on the Earth's climate, with the exception of the asteroid Chikshulub, which destroyed part of Mexico and killed the dinosaurs 66 million years ago. Computer simulations show that Chikshulub has thrown enough dust and sulfur into the upper atmosphere to eclipse sunlight and cool the Earth by more than 20 degrees Celsius and acidify the oceans. It took the planet centuries to return to its previous temperature, but then it warmed up another 5 degrees due to the ingress of carbon dioxide from the destroyed Mexican limestone into the atmosphere.

How volcanic activity in India affected climate change and mass extinction remains controversial.

Evolutionary changes

Scale: event dependent, cooling by about 5 degrees Celsius in the late Ordovician period (445 million years ago)

Timing: millions of years

Sometimes the evolution of new species of life will reset the Earth's thermostat. For example, photosynthetic cyanobacteria, which arose about 3 billion years ago, launched the process of terraforming, releasing oxygen. As they spread, the oxygen content in the atmosphere was increasing 2.4 billion years ago, while the levels of methane and carbon dioxide dropped sharply. Over the course of 200 million years, the Earth has turned into a "snowball" several times. 717 million years ago, the evolution of ocean life, larger than microbes, triggered yet another series of snowballs - in this case, as organisms began releasing detritus into the ocean depths, taking carbon from the atmosphere and hiding it at depths.

When the earliest land plants appeared about 230 million years later in the Ordovician period, they began to form the earth's biosphere, burying carbon on the continents and extracting nutrients from land - they washed into the oceans and also stimulated life there. These changes appear to have led to the Ice Age, which began about 445 million years ago. Later, in the Devonian period, the evolution of trees, coupled with mountain building, further reduced carbon dioxide levels and temperatures, and the Paleozoic Ice Age began.

Large igneous provinces

Scale: warming from 3 to 9 degrees Celsius

Timing: hundreds of thousands of years

Continental floods of lava and underground magma - the so-called large igneous provinces - have resulted in more than one mass extinction. These terrible events unleashed an arsenal of killers on Earth (including acid rain, acid fog, mercury poisoning and ozone depletion), and also led to a warming of the planet, releasing huge amounts of methane and carbon dioxide into the atmosphere - faster than they could. handle thermostat weathering.

During the Perm catastrophe 252 million years ago, which destroyed 81% of marine species, underground magma set fire to Siberian coal, raised the carbon dioxide content in the atmosphere to 8,000 parts per million and warmed up the temperature by 5-9 degrees Celsius. The Paleocene-Eocene Thermal Maximum, a smaller event 56 million years ago, created methane from oil fields in the North Atlantic and sent it skyward, warming the planet 5 degrees Celsius and acidifying the ocean. Subsequently, palm trees grew on the Arctic shores and alligators basked. Similar emissions of fossil carbon occurred in the late Triassic and early Jurassic - and ended in global warming, ocean dead zones and ocean acidification.

If any of this sounds familiar to you, it is because anthropogenic activities today have similar consequences.

As a group of Triassic-Jurassic extinction researchers noted in April in the journal Nature Communications: "We estimate the amount of carbon dioxide emitted into the atmosphere by each magma pulse at the end of the Triassic is comparable to the forecast of anthropogenic emissions for the 21st century."