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Breaching a “carbon threshold” could lead to mass extinction

Breaching a “carbon threshold” could lead to mass extinction

In the brain, when neurons fire off electrical signals to their neighbours, this happens through an “all-or-none” response. The signal only happens once conditions in the cell breach a certain threshold.

Now an MIT researcher has observed a similar phenomenon in a completely different system: Earth’s carbon cycle.

Daniel Rothman, professor of geophysics and co-director of the Lorenz Center in MIT’s Department of Earth, Atmospheric and Planetary Sciences, has found that when the rate at which carbon dioxide enters the oceans pushes past a certain threshold — whether as the result of a sudden burst or a slow, steady influx — the Earth may respond with a runaway cascade of chemical feedbacks, leading to extreme ocean acidification that dramatically amplifies the effects of the original trigger.

This global reflex causes huge changes in the amount of carbon contained in the Earth’s oceans, and geologists can see evidence of these changes in layers of sediments preserved over hundreds of millions of years.

Rothman looked through these geologic records and observed that over the last 540 million years, the ocean’s store of carbon changed abruptly, then recovered, dozens of times in a fashion similar to the abrupt nature of a neuron spike. This “excitation” of the carbon cycle occurred most dramatically near the time of four of the five great mass extinctions in Earth’s history.

Scientists have attributed various triggers to these events, and they have assumed that the changes in ocean carbon that followed were proportional to the initial trigger — for instance, the smaller the trigger, the smaller the environmental fallout.

But Rothman says that’s not the case. It didn’t matter what initially caused the events; for roughly half the disruptions in his database, once they were set in motion, the rate at which carbon increased was essentially the same.  Their characteristic rate is likely a property of the carbon cycle itself — not the triggers, because different triggers would operate at different rates.

What does this all have to do with our modern-day climate? Today’s oceans are absorbing carbon about an order of magnitude faster than the worst case in the geologic record — the end-Permian extinction. But humans have only been pumping carbon dioxide into the atmosphere for hundreds of years, versus the tens of thousands of years or more that it took for volcanic eruptions or other disturbances to trigger the great environmental disruptions of the past. Might the modern increase of carbon be too brief to excite a major disruption?

According to Rothman, today we are “at the precipice of excitation,” and if it occurs, the resulting spike — as evidenced through ocean acidification, species die-offs, and more — is likely to be similar to past global catastrophes.

“Once we’re over the threshold, how we got there may not matter,” says Rothman, who is publishing his results this week in the Proceedings of the National Academy of Sciences.“Once you get over it, you’re dealing with how the Earth works, and it goes on its own ride.”

A carbon feedback

In 2017, Rothman made a dire prediction: By the end of this century, the planet is likely to reach a critical threshold, based on the rapid rate at which humans are adding carbon dioxide to the atmosphere. When we cross that threshold, we are likely to set in motion a freight train of consequences, potentially culminating in the Earth’s sixth mass extinction.

Rothman has since sought to better understand this prediction, and more generally, the way in which the carbon cycle responds once it’s pushed past a critical threshold. In the new paper, he has developed a simple mathematical model to represent the carbon cycle in the Earth’s upper ocean and how it might behave when this threshold is crossed.

Scientists know that when carbon dioxide from the atmosphere dissolves in seawater, it not only makes the oceans more acidic, but it also decreases the concentration of carbonate ions. When the carbonate ion concentration falls below a threshold, shells made of calcium carbonate dissolve. Organisms that make them fare poorly in such harsh conditions.

Shells, in addition to protecting marine life, provide a “ballast effect,” weighing organisms down and enabling them to sink to the ocean floor along with detrital organic carbon, effectively removing carbon dioxide from the upper ocean. But in a world of increasing carbon dioxide, fewer calcifying organisms should mean less carbon dioxide is removed.

“It’s a positive feedback,” Rothman says. “More carbon dioxide leads to more carbon dioxide. The question from a mathematical point of view is, is such a feedback enough to render the system unstable?”

An inexorable rise

Rothman captured this positive feedback in his new model, which comprises two differential equations that describe interactions between the various chemical constituents in the upper ocean. He then observed how the model responded as he pumped additional carbon dioxide into the system, at different rates and amounts.

He found that no matter the rate at which he added carbon dioxide to an already stable system, the carbon cycle in the upper ocean remained stable. In response to modest perturbations, the carbon cycle would go temporarily out of whack and experience a brief period of mild ocean acidification, but it would always return to its original state rather than oscillating into a new equilibrium.

When he introduced carbon dioxide at greater rates, he found that once the levels crossed a critical threshold, the carbon cycle reacted with a cascade of positive feedbacks that magnified the original trigger, causing the entire system to spike, in the form of severe ocean acidification. The system did, eventually, return to equilibrium, after tens of thousands of years in today’s oceans — an indication that, despite a violent reaction, the carbon cycle will resume its steady state.

This pattern matches the geological record, Rothman found. The characteristic rate exhibited by half his database results from excitations above, but near, the threshold. Environmental disruptions associated with mass extinction are outliers — they represent excitations well beyond the threshold. At least three of those cases may be related to sustained massive volcanism.

“When you go past a threshold, you get a free kick from the system responding by itself,” Rothman explains. “The system is on an inexorable rise. This is what excitability is, and how a neuron works too.”

Although carbon is entering the oceans today at an unprecedented rate, it is doing so over a geologically brief time. Rothman’s model predicts that the two effects cancel: Faster rates bring us closer to the threshold, but shorter durations move us away. Insofar as the threshold is concerned, the modern world is in roughly the same place it was during longer periods of massive volcanism.

In other words, if today’s human-induced emissions cross the threshold and continue beyond it, as Rothman predicts they soon will, the consequences may be just as severe as what the Earth experienced during its previous mass extinctions.

“It’s difficult to know how things will end up given what’s happening today,” Rothman says. “But we’re probably close to a critical threshold. Any spike would reach its maximum after about 10,000 years. Hopefully, that would give us time to find a solution.”

“We already know that our CO2-emitting actions will have consequences for many millennia,” says Timothy Lenton, professor of climate change and earth systems science at the University of Exeter. “This study suggests those consequences could be much more dramatic than previously expected. If we push the Earth system too far, then it takes over and determines its own response — past that point there will be little we can do about it.”

Materials provided by Massachusetts Institute of Technology

 

Antarctica Glaciers

The science behind climate change

The earth’s climate has changed drastically over the decade. Geostationary satellites revolving around our planet help us see the big picture (quite literally), accumulating data constantly and updating us about the conditions of the Earth. Be it from the melting of polar ice caps to erratic monsoons and weather changes, and most definitely warming up of oceans to rise of sea levels. These events essentially indicate the dire condition of the climate all around the globe and its immediate need for attention.

The evidence behind climate change

  • Rising temperatures

Global warming is not a phenomenon we are unfamiliar with. It has had serious implications on our planet in various ways in the last decade and even before. Erratic rainfall, severe droughts, rising sea levels, etc. the main reason behind the rising of temperature was the increase in CO2 levels which was again caused due to pollution. In fact, the last decade 2000-2009 was the hottest on record.

Global Temperature

  • Ocean acidification

Since the industrial revolution swept through our planet bringing in new opportunities, adversely it has brought about some pretty serious implications on our large water bodies. The acidity in ocean waters has increased by 30%. This is due to the CO2 which is being expelled in greater quantities and in turn being absorbed into the oceans. The amount increasing per year is a whopping 2 billion tons per year. And that is just the upper layer of oceans.

  • Extreme events

Certain events occurring around the globe have captured the attention of various environmentalists and scientists, such as in the United States the number of recorded high-temperature weather phenomenon has been increasing. On the other hand, the number of low-temperature weather phenomenon has been decreasing since 1950. The number of intense rainfall conditions has also increased in this time period.

  • Shrinking glacial cover

From the snowy peaks of Himalayas to the Andes, the Rockies, Alps, etc. glaciers are decreasing everywhere around the world. This is a serious indication of climate change and poses serious threats to sea levels and mountain animals. Even islands remain in threat of disappearing completely under the rising sea levels. Satellite observations have revealed how much of this is true. In the past five decades, the snow cover has melted over the Northern Hemisphere.

  • NASA’s data

The ice sheets that form a huge landmass of Greenland and Antarctica have diminished in mass. According to NASA’s Gravity Recovery and Climate Experiment data, every year the loss of ice is 281 billion tons between 1993 and 2016. In Antarctica, the loss is 119 billion tons in that same time period. On top of that, the rate of ice mass loss in Antarctica has tripled in the last ten years.

 

Signs and Science behind climate change

The various compounds, whose abrupt increase in our environment which has caused changes in our climate are CO2, CH4, N2O, O3, etc. Their formations have been explained below:-

6 O2 + C6H12O6 --------> 6 H2O + 6 CO2 + energy

This is the process of combustion during which O2 reacts with glucose (C6H12O6) to produce water (H2O) and CO2. These chemical reactions occur when organic matter burns in our environment releasing chemical energy in the form of heat and light.

CH3COOH --------> CO2 + CH4

This is the microbial process of methanogenesis during which acetate (CH3COOH) is split into CO2 and Methane (CH4). Methane has the greatest impact on freshwater wetlands and rice paddies. The amount of methane produced in these fields increases with the area of land required for these rice paddies. This is the direct impact of the human population on climate change.

Nitrous oxide (N2O) is another contributing factor which is formed as a by-product of nitrification and denitrification.

CH4 + 4O2 --------> HCHO + H2O + 2O3

Smog is another pollutant that causes irritation of eyes and lungs, especially in city inhabitants. Tropospheric ozone (O3) is a constituent of smog that causes the mentioned problems.

NO2 + sunlight --------> NO + O

O + O2 --------> O3

NO2 + O2 --------> NO + O3

This is another process by which tropospheric ozone is emitted from atmospheric nitrate (NO2). First, the breakdown of nitrate occurs from which nitric oxide (NO) and an atom of oxygen (O) is obtained. After that, it combines with O2 and produces O3. Depicted above is the basic science behind climate change.

Random Quiz

Which of the following is not a greenhouse gas?

Correct! Wrong!

In order, the most abundant greenhouse gases in Earth's atmosphere are Water vapor, Carbon dioxide, Methane, Nitrous oxide, Ozone, Chlorofluorocarbons (CFCs) and Hydrofluorocarbons (incl. HCFCs and HFCs). Carbon Monoxide does not cause climate change directly.


Main reasons behind climate change

We might not be able to notice changes in our Earth’s climate and enjoy it as normal. However, the Earth’s climate is ever-changing, more rapidly in these times than ever so before as seen in the geological record. There are a lot of reasons behind climate change and a lot of factors, natural and anthropogenic (human-induced) which has contributed to this. The rapid rate of climate change is now a great concern worldwide.

Here are some of the main reasons behind climate change:

  1. Human activity
    • We, humans, are the ones who emitted greenhouse gases in the atmosphere since the industrial revolution. This led to more heat retention and absorption which in turn, increased surface temperatures.
    • We have emitted aerosols and these, after scattering in the atmosphere have absorbed solar and infrared radiation, which has had an adverse effect on the microphysical and chemical properties of clouds.
    • We have also changed the usage of lands, deforested them, which in turn led to a greater amount of sunlight being reflected from the surface of the earth back into space also known as the surface albedo.
Haiti Deforestation

Satellite image showing deforestation in Haiti, Haiti-Centre. This image depicts the border between Haiti (left) and the Dominican Republic (right). (Source: NASA)

  1. Solar Irradiance

Since the Sun is our nearest star and our most fundamental source of energy, it does have the effect that is instrumental to our climate changes. The Ice Age between 1650- 1850 in Greenland was due to the littlest decrease in solar activity. From 1410-1720 it was cut-off by ice and all the Glaciers shifted in and moved towards the Alps.

  1. Tectonic movements of plates and volcanic activity

Tectonic plates form the very basis of our continents and even the slightest movement can cause them to move to very different positions from their initial location. These plate movements can cause eruptions in volcanoes which in turn contribute to climate change.

The eruptions from volcanoes which consist of gases and dust particles may warm or cool the Earth’s surface altering it’s temperature significantly.

  1. Changes in ocean currents

Ocean currents carry heat to all the other water bodies of the Earth. Hence, the change in direction of these currents can change affecting the warmth or coolness of various continents. These can have a relatively large effect on our overall climate (including coastal climate and global too) because oceans harbor a large amount of heat.

These are some of the main reasons behind climate change.

Remedies for climate change

We, as humans should individually take measures to save our planet Earth and so that our climate is not affected as much.

  • Instead of depleting our reserved fossil fuels, we need to use more renewable resources such as wind, wave, tidal and solar energy.
  • We need to make use of more public transport instead of our private vehicles. We need to gradually replace our petrol driven vehicles with electric ones in the future to reduce the emission of toxic gases in the atmosphere.
  • One of the easiest steps our government can take is cutting methane emissions. Methane is 84 times harmful than carbon dioxide emissions and is a much greater reported problem.
  • We should wisely use our available energies. We can do this by using energy-efficient light bulbs, unplugging computers and other electronic devices when not in use, washing clothes in cold water instead of warm, using natural sunlight to dry our clothes instead of dryers, etc.
  • Focusing our lives in nature rather than consuming and purchasing. If we start practicing composting, recycling, sharing, fixing and making our lives would be greener and cleaner and would significantly enrich nature and our lives in the process.
  • Carbon pricing so that polluting nature has a heavy price. It might sound not as much of an important step but it paves the way for greener solutions. As agreed by market economists, carbon pricing is also a business-friendly way to decrease pollution in nature. The federal needs our individual support to help make this possible.
  • We should consume more organic meals and less meat. By doing so, we will help ourselves to a better diet and also our planet to make it more climate-stable. We should also try growing our own food and never waste it as much as possible.

Final Words

Scientists all around the globe belonging to various scientific societies have published numerous statements, coming to the unanimous conclusion that global warming is the primary factor of climate change and that we, humans are the primary cause. We should definitely stop overloading our atmosphere with carbon dioxide (CO2), which we do when we burn fossil fuels like oil and coal to provide ourselves electricity to power our transports and keep our homes warm. The Earth is steadily warming up in response and this is a dire situation whose consequences will affect us in the very near future in drastic ways.

Read More:

  1. Climate change: How do we know?
  2. Climate change, global warming and greenhouse gases