Stochastic resonance in climate: IIT professor explains how Earth switches between ice age and greenhouse periods

Climate change and global warming are now the greatest challenges we face and must be managed very carefully to keep our world livable for future generations. Bill Gates once mentioned that if we don’t become vigilant on this critical issue from now on, we are going to face a disaster that would be far worse than the corona pandemic situation we have faced over the past two years. .

This comment emphasizes that the evolution of the atmosphere towards a higher temperature is mainly affected by human activities that cause damage to nature. Thus, it is obvious that in this case the inhabitants of nature somehow control the state of their habitat. However, there is a very interesting colossal shift in the earth’s climate that is regulated by nature itself.

This extended transition in the Earth’s atmosphere is triggered by a characteristic resonance phenomenon that I will shed light on in this article.

LONG-TERM TEMPERATURE VARIATION ON EARTH

The Earth was formed more than 4.5 billion years ago. From our geography lessons in school, we all know that when our planet was born, there was a burning gaseous fireball. Then, after gradually radiating heat over time, it came to the current state.

There is no doubt that this is true. However, if we see it at a finer level, we will understand how far more fascinating the pattern of global atmosphere change is.

It is not as if the average temperature of the earth’s atmosphere has settled after starting to decrease from a very high value at the initial stage, or it will constantly increase due to global warming according to the current situation.

The variation in the average temperature of the earth’s surface sometimes follows a periodic pattern, sometimes a diversified trend over time. One thing to keep in mind is that the climate transition I’m talking about is happening on a geologic timescale. Thus, it will not be possible to experience this change in our lives, but we can try to understand this interesting aspect of nature.

The Earth’s climate essentially switches between two phases; one is the “Ice Age” and the other is the “Greenhouse Period”.

Almost every one of us has an imagined image of the Ice Age in our minds that mostly comes from our connection to fantasy stories. Whenever the term “Ice Age” enters our ears, we begin to visualize our world as a gigantic ball of ice with giant, fur-covered animals wandering around. This impression is not entirely accurate.

During the Ice Age, the temperature of the earth’s surface and the air level above it remains relatively low, so that ice sheets and glaciers exist in the polar regions, continental lands and places of higher altitude. On the other hand, during the greenhouse period, the average temperature of the earth becomes very high and there is no trace of ice left on the surface of the earth.

So, even if it is surprising, it is true that we are currently living in an ice age (Quaternary ice age) which is the fifth consecutive since the birth of this planet and which began approximately 2.5 million years ago. years.

The existence of ice at both poles, in some parts of the continents and on mountain tops confirms this fact.

WHAT HAPPENS DURING AN ICE AGE?

Now we come into the discussion of the Ice Age. The Earth’s average temperature does not remain stable for the duration of a particular ice age. In fact, it periodically changes between higher and lower values.

So, ethere are two phases; a colder period and a warmer period in a given ice age; the first is called the “glacial” period and the second is called the “interglacial” period. During the ice age, almost the entire surface of the earth was covered in ice and this is the image that is created in our minds in connection with the term “ice age”.

So, roughly speaking, what we call “the ice age” is really part of it; one of the two phases that constitute it. The other, i.e. the interglacial period has great significance for us as we enjoy our life in this particular phase.

It is at the will of the universe that the transition between glacial and interglacial phases occurs periodically. The time scale of this change is of the order of hundreds of thousands of years. Many mysteries lurk in every corner of nature and human beings have been trying to unravel them since the very beginning of their existence.

So, very naturally, scientists began to search for an answer to the question, “What is the reason for these periodic and drastic changes in climate during the Ice Age?”

The logical way to identify the triggering factor for this periodic weathering is to look for influential environmental factors that follow a similar pattern in their temporal variation.

It has been found by researching that the single change in Earth’s orbital eccentricity due to the gravitational effect of the entire universe has the same astronomical scale periodicity as that of the transition between glacial and interglacial.

But, here we have to consider another crucial aspect; the trigger motor force. For example, a person may have particular ideas and opinions, but may not be very good at influencing others. Similarly, in this case, it was also found that the force of the periodic change in Earth’s orbital eccentricity is not strong enough to cause drastic changes in climate. Therefore, further investigations continued.

Following this, an explanation of a new type of phenomenon has been introduced into the world of science, and it has been named “stochastic resonance”. We know the term “resonance” from our physics textbooks, in connection with the discussion of oscillations.

Roughly, when the frequency of an oscillator is equal or proportional to that of the external forcing acting on it, the propagation of the oscillation increases enormously; this is called resonance. That’s how when the thoughts of two friends agree, the spirit of their minds becomes a hundredfold.

WHAT IS “STOCHASTIC”?

Now we need to explain what “stochastic” is. It is linked to the statistical description of unpredictable events. Let’s not get into a serious scientific discussion about this.

Just keep in mind that a new type of force had to be considered to explain the glacial-interglacial transitions. This force exhibits uncertain temporal variations and is associated with annual fluctuations in solar radiation.

However, to explain the phenomenon of oscillation between glacial and interglacial, scientists have modeled it as a transition between the two states of an oscillator; the states representing the colder and warmer periods of an ice age that are separated by a barrier.

So ultimately it’s a story of breaking that barrier for climate change to happen and that can only happen when the time scale of the transition between the two states caused by the fluctuating force matches at the low motor oscillation period.

This causes a resonance in climate change, resulting in glacial-interglacial transitions.

Although first introduced to explain climate change during an ice age, the underlying principle of stochastic resonance has established a very crucial mechanism in which the random force we sometimes call “noise” can awaken a signal of weak sleep if applied with appropriate force. It has a large number of technological applications which are in the continuous process of development.

So noise that is mostly unwanted can work constructively to improve the outcome if administered at the right scale. Therefore, it is a lesson of nature for us; we have to have a sense of moderation to make things work.

Written by Dr. Moupriya Das, Assistant Professor, School of Basic Sciences, IIT Mandi.

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