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Apocalypse & Armageddon

The apocalypse is in doubt: the current climate change was milder than the previous

The apocalypse is in doubt: the current climate change was milder than the previous 1

In the last two millennia, there have been two periods of global cooling, which led to rapid fluctuations in sea level – up to 4.23 millimeters a year. This is noticeably stronger than today. It turns out that the current climate change is not unprecedented in the history of mankind. And past sea retreats could cause as many as two civilizational crises. Let’s try to understand why this is important for us now.

Volcanic eruptions, along with other factors, could cause a couple of severe cooling, during one of which the Roman Empire collapsed.  Traces of them were found on a distant Maldivian atoll / © Wikimedia Commons

Volcanic eruptions, along with other factors, could cause a couple of severe cooling, during one of which the Roman Empire collapsed. Traces of them were found on a distant Maldivian atoll / © Wikimedia Commons

Sea level: different everywhere, despite the law of communicating vessels

Usually we imagine the sea level as something unshakable and the same throughout the planet. This is not so: the sea level in Ireland is more than 150 meters higher than that of the Maldives, and even its current rise in some places is faster, but in some exactly the opposite: there the average sea level “sinks”.

The apocalypse is in doubt: the current climate change was milder than the previous 2
It can be clearly seen that in the region of New Guinea, the sea is more than 80 meters above the average planetary level, and in the Maldives – more than 100 meters lower / © Wikimedia Commons

At first it seems that this contradicts the law of communicating vessels: after all, the oceans are one, and water from a higher place should flow to a lower one, leveling the surface. In fact, there is no contradiction. Our planet is not a sphere, but a geoid, and those parts of it where the sphere is slightly “hewn” have a different surface shape. Limitations from gravity and the shape of the Earth create a huge, up to a couple of hundred meters, difference in sea level in different places.

The red places of the greatest convexity of the geoid, the blue - the places of its greatest concavity / © Wikimedia Commons
The red places of the greatest convexity of the geoid, the blue – the places of its greatest concavity / © Wikimedia Commons

In order not to get confused and understand what is happening on the planet as a whole, they use the concept of global sea level. All the irregularities of the geoid are averaged in it, which makes it possible to obtain a single measure of the change in the “average” sea level.

So, until the 1980s it grew by 1.8 millimeters a year, and since the 1980s – by 3.2 millimeters a year (now 3.3 millimeters). The value itself is small, but there are places where, due to the local specifics, the sea comes especially fast: say, in the Pacific Ocean.

Specifically, this has not affected badly on the islands of the Pacific Ocean: on the contrary, the area of ​​Tuvalu and Kiribati, recorded by satellite images, has grown. But, definitely, in the future somewhere on the Earth a situation may come when the rise of the sea will force the shore to be strengthened by pouring sand on it.

However, it should be remembered that the sea is able not only to advance, but also to retreat. And such processes can be even more dangerous.

Ancient Crisis: First Cooling

One of the most important properties of changes in sea level is that it clearly reflects what is happening with the climate. If it changes, the sea changes with it. Due to global warming, the sea has risen to 21 centimeters since 1900 . Mainly due to the expansion of sea water from heating. Additional factors were the melting of parts of the ice of Greenland and other areas. Sea level rise is one of the key evidence of global warming.

The question arises: did the sea level change before that? Previous measurements on the Atlantic Ocean gave different data: somewhere, changes over the past two thousand years were recorded, somewhere not, and it seemed that all these fluctuations in any direction did not exceed 0.25 meters. Not very much, but still more than the current rise of the sea due to global warming.

The problem with these numbers is that they were calculated according to the level of salt water in coastal swamps. This is not a direct measurement of sea level, and it may contain significant errors. The data on the Pacific Ocean are scattered, not always clearly dated, and therefore a number of researchers consider them to be speculative.

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An international team of scientists recently published a work in Nature Geoscience , where they studied the coral atolls of the Maldives – islands in the Indian Ocean close to the equator. The advantages of this research point are that there is no noticeable tectonics; lowering and raising land for geological reasons are extremely slow. Coral atolls are rigidly connected to sea level: when it drops noticeably, corals at low tide are in the open air and die.

Maldives Atoll, on which samples of dated corals were collected / © Paul S. Kench et al.
Maldives Atoll, on which samples of dated corals were collected / © Paul S. Kench et al.

In addition, the authors used the exact uranium-thorium dating of ancient corals. It is based on the fact of the decay of uranium with the formation of thorium atoms: and, since the rate of such decay is known, it allows you to accurately calculate the chronological framework of sea level changes (more precisely than in most previous work on the topic).

One of the sampling points for coral samples at the measurement stage / © Paul S. Kench et al.
One of the sampling points for coral samples at the measurement stage / © Paul S. Kench et al.

It turned out that in 2000-100 BC, the sea level in the Maldives was 0.5 meters above the average in our era, which also means a fairly warm climate. In the years 234-605 AD, the level began to fall sharply, at a minimum it was 1.34 meters below the current average sea level. Two samples even indicated a level 1.45 meters lower than the current one.

The event lasted 371 years and can not be explained by anything other than a noticeable drop in temperature in the equatorial regions of the Indian Ocean. Equatorial waters are often more sensitive to warming, since the water in them rises faster, expanding and leading to the onset of the sea – but the same pattern works in the opposite direction.

It turns out that in the years 234-605 the planet could have been noticeably colder than today. Interestingly, this period coincides with the decline and collapse of the Roman Empire and the Great Migration of Peoples.

The decline of the Roman Empire is associated by historians with systematic crop failures, which often lasted several years in a row / © Wikimedia Commons
The decline of the Roman Empire is associated by historians with systematic crop failures, which often lasted several years in a row / © Wikimedia Commons

Previously, on the basis of narrow tree rings (the norm during cooling), other scientific groups have already put forward the hypothesis of the “Late Antique Small Ice Age”. However, then it was about the 500-600s, and there was no data for an earlier time. Now it becomes clear that the cooling could begin in the III century, coinciding in time with the crisis of ancient civilization.

The authors of the study note that it is on these 371 years that the 13 coldest decades of the last two thousand years are accounted for. Since colder periods normally coincide with a decrease in rainfall, they should have had catastrophic consequences for agriculture in the form of droughts and crop failures.

After the 7th century, corals in this zone do not grow until the 15th century: the authors believe that sea levels have risen at least to the present or even higher, not giving the local coral reefs enough light to grow.

New time: the second wave of cooling

In the years 1481-1807, the Maldives experienced a second period of low sea level: on average, at that time it was 0.71 meters lower than today. By 1807, the level reached a minimum – 0.89 meters below the modern average. It should be emphasized that the fall of the sea in the Maldives both in modern times and in antiquity is noticeably stronger than its rise during modern global warming.

Illustration of February from the French watch book of 1412-1416.  Light clothes, thin snow, and all this in the midst of winter.  In the illustrations of the remaining, less severe months, there is no snow at all.  It seems that as early as the beginning of the 15th century, the climate in Europe was quite warm / © Wikinedia Commons
Illustration of February from the French watch book of 1412-1416. Light clothes, thin snow, and all this in the midst of winter. In the illustrations of the remaining, less severe months, there is no snow at all. It seems that as early as the beginning of the 15th century, the climate in Europe was quite warm / © Wikinedia Commons

Only in 2017, the sea level in the Maldives rose by 0.89 meters, that is, it reached the present. Over 210 years of anthropogenic global warming, the sea has grown by the same amount by which it retreated for much shorter periods of time in the III-VII and XV-XIX centuries.

The peak sea retreat recorded in the work for the last two thousand years is 2.8 millimeters per year. The peak rate of sea level rise today is 3.4 millimeters per year (this is the limit, usually called 3.3 millimeters per year). From this it is clear that the current offensive of the sea in speed is comparable to its retreat in the last thousand years.

In addition, after the retreat of the sea in late Antiquity, its rapid offensive followed – and by the beginning of the 700s, according to work, the rate of offensive of the sea was 4.23 millimeters per year, that is, significantly more than today.

It is no less interesting that specifically in the case of the Maldives, the current sea level is still significantly below the level of the heyday of the ancient world – 2000-100 BC (a difference of half a meter).

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Canals of Holland, XVII century.  Clothing is noticeably warmer than in the Middle Ages.  In Western Europe, the use of sleds has become normal / © Wikinedia Commons
Canals of Holland, XVII century. Clothing is noticeably warmer than in the Middle Ages. In Western Europe, the use of sleds has become normal / © Wikinedia Commons

The events of the New Age – this period is also called the “Little Ice Age” – included a series of wars and famine years. The most cruel of them belong to the first half of the 17th century, when a series of several hungry years led to the Time of Troubles in Russia, and the German population fell from 50 to 70% from a combination of wars and starvation.

Definitely, this is also very similar to the civilizational crisis. Key countries of 1481, such as Spain, Portugal, leading Italian republics such as Venice, Florence and Genoa, by 1807 became only a pale shadow of themselves, and China was so weak that it experienced the conquest of another wave of barbarians.

Nevertheless, a number of other states have noticeably strengthened their positions during this time. England, France and Russia by 1807 became significantly larger, had more population and opportunities. True, in all three cases, this coincided with the active territorial expansion of these states, which allowed them to obtain resources that were not there in 1481.

Why is it important

The sea cannot recede either by 89 centimeters (peak value from work), or by 0.7 meters (average value for two cold periods), if there is no cooling. Today, the Maldives atolls are the most accurate measured at sea level over the past thousand years.

And from measurements on local corals, it follows that during this time there were two rather strong cooling, in amplitude similar to the current warming. In terms of speed – judging by the record sharp retreat of the sea by 2.8 millimeters per year – these cooling could even come faster than the current warming.

Meanwhile, a work was published earlier in 2019 that generally denied the very reality of the small ice age of the New Time, as well as of the Late Antique small ice age. Its authors argued that the most reliable signs of cold weather in the small ice age for different regions occurred at different times, therefore, as a whole, the temperature on Earth as if did not change.

Fluctuations in sea level of up to 0.89 meters indicate the extreme doubtfulness of this conclusion, often made on the basis of historical records or indirect temperature indicators. Sea level is a more reliable measure of global temperatures than indirect evidence.

The authors of the new article note that their predecessors could not get accurate data on sea level changes in other places, mainly because coral reefs have been actively growing over the past 200 years after rising sea levels. In the process of secondary growth, they often destroyed or mixed strongly the materials of older reefs, which were preserved only in a limited number of places with exceptionally favorable conditions such as the Maldives. That is, the method used in their work allows a deeper and more realistic assessment of changes in the climate of past centuries.

Unprecedented climate change? Does not look like

Researchers conclude with the conclusion: “The magnitude and speed of sea level changes in the present Indian Ocean are not unprecedented over the past 2000 years.” These words look dry and mean – in fact, this is a scientific journal, what else can its text be in style?

But there is a lot to them. If the sea in the last 20 centuries receded at a speed of up to 2.8 millimeters per year, and came at a speed of 4.23 millimeters per year, then it turns out that its current growth of 3.3 millimeters per year is not only not unprecedented, but also quite moderate. The authors believe that the antique period of sea level for the Maldives (half a meter higher than the present) will be achieved only in the 21st century.

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More importantly, temperature changes in the pre-anthropogenic era, when people could not influence the climate as they are today, are comparable in scale to the current ones. This is a very unpleasant sign. Accidental climate fluctuations such as the Late Antique or Small Ice Age can lead to alarming consequences in the form of high cold mortality (and it is much higher than mortality from heat), crop failures and droughts.

It would be nice to sort out and find out the exact culprit of the events of those years – in order to try to avoid repeating them. Or at least not to be taken by surprise.

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