Sea level rise and inundation of coastal India
Dr Nachiketa Das
Director,
NRI-Enviro-Geo-
(First published
on
Global warming
is making sea level rise. Sea level,
however, will not rise appreciably overnight, not in months, not even in
years. The rise will assume dangerous
proportions only over a substantial length of time, perhaps over decades. The assertions are not designed to make you
complacent my readers, but you need not panic either. The sensationalist movies and documentaries
that you have been watching show the sea invading deep into eastern
Sea and nature
in general, have been more kind to us human beings, than we would care to
admit. Nature always gives us plenty of
warning before doing anything drastic, and by the same token, sea gives us a
good many years to protect our landmass from her transgression. As sea level rise accelerates due to global
warming, coastal
Rate of sea level rise
Earth-scientists
equipped with geological, geochemical and palaeontological (from the study of
fossils) evidences have proved the existence of ice ages in earth’s
history. During an ice age the
temperature of the earth’s surface and atmosphere decline significantly that
cause substantial accumulation of glacial ice.
The most recent ice age in the earth’s history commenced around 110,000
years ago, peaked around 20,000 years ago, and ended around 10,000 years
ago. While stating these ages I have
deliberately provided round numbers in consideration of the fact that at
different parts of the globe the last ice age peaked and ended at somewhat different
times. If I may further elaborate on the
regional variation, I could even state that the last ice age actually ended
anywhere between 10,000 to 15,000 years ago.
Soon after the ice age reached the maximum, glaciers started melting and released vast quantities of water into the sea. Consequently sea level started rising, and has risen about 130 m in the last 18,000 years. The rate of sea level rise in time, however, has not been uniform; initially it was very fast, and then it slowed down. Most of the sea level rise, therefore, took place between 18,000 and 6,000 years before present. Let me clarify the commonly used term in earth-science ‘before present’, which is precisely what it says, and means ‘ago’ in common parlance.
Since 3,000 years before present till the end of the nineteenth century (1900 AD), sea level was practically constant, and did not rise much. The rate of sea level rise during this period was a mere 0.1 to 0.2 mm per year. Since 1900 AD, however, sea level has been rising more rapidly, at the rate of 1 to 2 mm per year. These numbers in millimetre do not appear large and daunting, but when accumulated say over a period of a century they do assume a menacing proportion. In the last 100 years since 1900 AD, sea level has risen by 20 cm, which is not insignificant.
In the early
1990s satellite altimetry was employed to very precisely record sea level
rise. Let me explain here briefly
satellite altimetry, which is an advanced piece of space technology for
accurate measurement of height.
Satellite altimetry very precisely measures the time taken by a radar
pulse to travel from the satellite antenna to an exact point on the surface of
earth and back to the satellite receiver.
These data eventually provide the exact height. TOPEX/Poseidon joint satellite mission
between NASA of the
A logical question that arises now is precisely how high will sea level rise to, say by the end of the twenty-first century? This is a difficult question to answer, and many groups worldwide are already engaged in this activity, but let us make an attempt here none the less. If the current rate of sea level rise, as ascertained from satellite altimetry, remains constant at 3.1 mm per year then by 2100 AD the rise would be 310 mm or 31 cm. If this current rate of sea level rise were to remain unchanged indefinitely, there is not really much cause for concern for the near future. The current rate however, is extremely unlikely to remain constant for the next one hundred years. The calculated projection of sea level rise by 31 cm by the year 2100 AD, therefore, is far too naïve. Moreover, we know that the intensifying anthropogenic global warming would considerably accelerate the rise of sea level through two main processes: increased pace of widespread melting of glacial ice, and thermal expansion of sea water.
I suppose
everyone understands rise in sea level due to melting of glacial ice but the
phenomenon of sea level rise due to thermal expansion, although quite simple,
may be somewhat unknown. So let me start
with an explanation of thermal expansion, which is essentially a property of
any matter, solid or gas or liquid, to expand when heated. Sea water, which has a huge capacity to
absorb heat, is no different, and expands in volume upon heating, thus raising
sea level. If sea water temperature
rises by say 1oC by 2100 AD, resultant rise in sea level could reach
40 cm. A near complete melting of all
the mountain glaciers of the world would make sea level rise by about 35 cm,
which could well happen by 2100 AD if global warming continues unabated. So a combination of these two factors alone
could raise sea level by 75 cm by 2100 AD.
Let us now analyse the contributions from
A just reported (September 2008) authoritative study claims that Greenland Ice Cap that currently experiences losses of 257 cubic km of ice per year due to melting, would loose 465 cubic km of ice annually by the year 2080 AD. Melt water from this body of ice raises sea level by 0.6 mm per year now, and would rise to 1.0 mm annually by 2080 AD. On the basis of this study if we arbitrarily accept contributions from Greenland Ice Cap to raise sea level by 0.6 mm per year till 2050, which then rises to 0.8 mm per year till 2080, and finally to 1.0 mm per year till 2100 AD, we get a sea level rise of 7.5 cm by 2100 AD [(0.6 mm X 50 years) + (0.8 mm X 30 years) + (1.0 mm X 20 years) = 74 mm = say 7.5 cm in 100 years].
The southern
continent of
These simple
calculations of total contributions from all the sources that I have shown in
this article thus far, project a sea level rise of 90 cm by the year 2100 AD.
The uncertainty
in calculating the contributions from
The
Intergovernmental Panel on Climate Change (IPCC), which is currently chaired by
a scientist from
The IPCC-TAR
considered all the relevant factors of thermal expansion, mountain glaciers,
glacial ice of
Given my obsession with roundness, and quite rightly so, for the earth is round, the sun is round, the moon is round, and most importantly cricket ball is round, let us accept again a round figure of 100 cm or 1 m rise of sea level by 2100 AD for our ensuing discussions, instead of 90 cm that I have demonstrated earlier in the text.
Sea level rise is not uniform
We all know that
water maintains the same level. We have
seen this fundamental property of water well exhibited everywhere, say in a cup
of tea, in a bucketful of water, and for that matter in a bigger container like
a swimming pool. How come then I claim
here that the level of sea water over the globe, or for that matter sea level
rise is not uniform? In order to explain
this apparent intrigue, I have to remind you my readers that the earth is a
fast spinning sphere, hurtling round the sun at a great speed. Let me expand a little on the speeds of this
vast spinning top, which is also a space-ship.
Any place on the
equatorial surface of earth, if viewed from a distance in the space, is
travelling at a speed of 1,670 km per hour, which is twice as fast as a jumbo
jet in full flight! I will show a simple
calculation to convince you of this great speed. The equatorial radius of earth is 6,378 km
which makes the equatorial circumference 40,076 km (2 X Pi X 6,378 km = 40,076
km). Any point on the equator covers
this distance during the course of one full day which is about 24 hours, at a
speed of 1,670 km per hour (40,076 ÷ 24 = 1670 km). The speed of revolution of earth round the
sun is even faster, and let me present the calculation to convince you.
Earth’s orbit is
elliptical, which requires calculating an average value for the radius for
calculating the circumference. The
average radius of 149.5 million km [(152 million km + 147 million km) ÷ 2] when
multiplied by 2 Pi gives a circumference of 939, 336, 203.4 km, say 940 million
km. Our space-ship earth covers this
distance in 365 days and 6 hours travelling at a speed of 107,000 km per hour
[940 million km ÷ (365.25 X 24 hours) = 107, 232 km per hour]. Our earth races round the sun at a speed at
least a hundred times faster than that of a commercial airplane, whose cruising
speed is no more than a 1,000 km per hour.
Having
demonstrated these calculations on the speeds of rotation and revolution of the
planet earth, I would like to veer off the main theme of this article, in order
to lavish praises on the Father of Astronomy Arya Bhatta (476 – 550 AD), who in
the fifth century AD that is over a millennium and a half ago very accurately
calculated many aspects of the spinning earth.
Arya Bhatta was very likely born in the erstwhile state of Kalinga,
which adjoined
Arya Bhatta’s
seminal work Aryabhatiyam was translated in to Arabic in the ninth century and subsequently
it journeyed further west. Four hundred
years later in the thirteenth century this treatise on astronomy was translated
into Latin. The Latin version of
Aryabhatiyam provided the foundation for growth of astronomy in
Coming back to
the issue of non-uniformity of sea level rise, I hope I have convinced my
readers that sea water is perched atop the vast space-ship called earth,
travels at a tremendous speed, and is held tightly by gravitational
forces. Earth’s gravity shows subtle
variations across the globe depending on subterranean composition. Sea water, thus experiences subtle variations
in gravitational pulls at different locations, which affect sea level. Moreover, earth’s rotation and the consequent
Coriolis force, and trade winds whip the sea water to different levels at
different places. For example sea level
is currently 50 cm higher than the mean sea level at various Indonesian islands
located between 0 and 10o S latitudes. Non-uniform changes in temperature and
salinity of sea water and ocean circulations also contribute to the spatial
variability in sea level.
Having convinced you of the spatial non-uniformity of sea level at any given point in time, let me assure you that at some places of the globe, sea level could even rise twice as high as the mean sea level rise.
Maximum possible rise of sea level
In order to
determine the maximum height sea level could rise to, we need to discuss the
total volume of ice present on our planet earth, which could completely
melt. The Antarctic landmass of 13.6
million square km holds 30.1 million cubic km of ice, which constitutes about
91.5 per cent of the total ice on earth.
The obvious
question that arises now is how long would sea level take to rise to the maximum
possible limit of another 80 m. We are
aware that after the last glacial maximum, since 18,000 years before present,
sea level rose by 80 m in about 8,000 years.
The rise was thus an even one meter in a hundred years, a rate of rise
identical to our projection for the twenty first century. Based on this rate we can as well say that
another 8,000 years will elapse before sea level rises to the maximum. This logic may not be correct though for the
simple reason that anthropogenic global warming has utterly disturbed the
global climate, which in turn has provided the momentum for an accelerated pace
of melting of glacial ice. If the rate
of melting of glacial ice doubles, which is a real possibility, and then
remains steady, which is unlikely, 80 m rise could happen in the next 4,000
years. If the rate of melting of glacial
ice continues to increase after doubling, sea level may rise to its maximum
potential even sooner, but certainly not before a couple of millennia.
Sea level rise and coastal inundation
Sea level rise
will devastate the low-lying coastal areas of the entire world. Mainland
The northern most
part of the east coast of
A 1 m rise of
sea level will inundate 1,810 square km of land in
Coastal inundation after the last ice age
Many people in
Although there
have been subsidence as well as uplift of land in this submerged continental
shelf off the coast of Gujarat, it is not unreasonable to attribute the depths
of the two underwater ruins essentially to sea level rise. Now let us make an attempt to ascertain the
age of submergence of Dwaraka based on information from global sea level
rise. A 15 m rise of sea level took
place over a period of 8,000 years, and 25 to 40 m rise took place over a
period of 10,000 years. On the basis of
these ages, I feel confident to state that Sri Krishna’s Dwaraka was inundated
at least 8,000 years ago. This
information also implies that the fratricidal war between the Kauravas and the
Pandavas, description of which constitutes the subject matter of the greatest
epic Mahabharata took place at least 8,000 years ago. This age contradicts, and quite rightly so,
the speculative age for the Mahabharata at 1,000 BC, which was proposed by the
nineteenth century Europeans, essentially British, whose prime interest was to
distort the history of
And to their
utter shame and disgrace, countless historians of
Ages of the
pieces of pottery recovered from the Gulf of Khambhat Cultural Complex (GKCC)
during underwater explorations in 2003 and 2004 by the scientists of National
Institute of Oceanography (NIO), determined in laboratories in
Having provided
an example of a massive submergence from the west coast, I present here another
small and interesting observation from the east coast of
During the last
ice age, I might as well record here that the snow line was much lower. The Himalayan range was of course all covered
with glaciers but mountains in the deep south of Tamil Nadu and Kerala also had
ice caps. Snowline in locations at 10o
latitude existed at 1,000 m above sea level, which means that the Nilgiris that
have an altitude of around 2,500 m today, hosted glaciers then. At 20o latitude snowline was down
to 600 m, which means that practically all the higher mountains of the
Aravalli, the Vindhya, the Western Ghat and the Eastern Ghat ranges were home
to glaciers. The Mahendra Giri of Orissa
at 1,200 m and the adjoining hills of the
Losses due to sea level rise
The rising seas now threaten to inundate the deltaic plains of the east coast of India, which are well and truly the bread baskets of the country, for they provide prime agricultural land. Agricultural productivity of these fertile tracts is often double the average productivity of the country. On the west coast, the rising seas threaten the vast commercial and industrial complexes. As sea level rises, coastal erosion will increase very substantially along the entire shoreline, ground-water quality will be compromised, and storm surges will become much more frequent as well as intense, destroying infrastructure.
In an earlier
article, Can Global Warming Make The
The economic aspect of global warming and sea level rise will probably emerge as a new interdisciplinary subject in the near future. In stead of attempting any calculations to put a price on coastal inundation due to sea level rise, I would merely make a generalised statement that the economic losses will run in to thousands of trillions of rupees.
Achyutananda’s prophecy on sea level rise
My forebear
Achyutananda Das, the fifteenth century Oriya poet, philosopher and yogi, was a
great seer. He was born in a village by
the name Nemala, where the distributaries of the mighty
The many books
of Achyutananda, which could loosely be termed as a collection of Books of
Prophecies, contain bold predictions of the sea inundating coastal Orissa. His prophecies describe in detail a week of
incessant rains and the events leading up to the marine transgression and
subsequent inundation of the sprawling stone stair case, comprising twenty-two
steps, of the Jagannath temple of Puri.
On
My grandfather used to describe me these prophecies, when I was only a child studying under his tutelage in the village primary school. I failed to comprehend the concept of marine transgression, and did not quite fathom the deluge then. Consequently I never really understood the prophecies. And as luck would have it, I moved to Puri for my high school education, and saw the Jagannath temple and the sea. I distinctly remember a classmate of mine who hailed from the township of Puri telling me of the prophecies again, which by the way are a part of the established folklore of the holy temple town since their issuance in the early part of the sixteenth century. My friend had quoted that the 65 m tall Jagannath temple will be submerged completely. I had dismissed his words out of hand; I never paid much attention to what he had said. Whenever I frolicked on the vast sandy beaches and on the premises of the Jagannath temple, I was most reluctant to accept that this revered temple could ever be so overwhelmed. I dismissed the prophecies as figments of imagination or superstition at best.
Only after I embarked upon my studies in earth sciences, which have now taken me to many parts of this magnificent planet we call home, and lodged me in quite a few venerable universities and institutions of the world, I learnt that marine transgression and regression are geological facts. Moreover they have occurred regularly in earth’s history. I realised that the sea level could indeed rise to inundate the Twenty-two Steps of the Jagannath temple, which are barely 10 to 15 m above sea level. In fact the deluge could entirely submerge the Jagannath temple that stands just about 80 m above sea level, as prophesied. As explained earlier in the text 80 m is in fact the upper limit of sea level rise should all the glacial ice of the world were to melt away. Call it a coincidence or a remarkably accurate prophecy by a remarkably accurate seer, the choice is yours. It is about time that the world knows of this very great seer.
On the 15th
of September 2008, only a month ago, a mere 100 km per hour storm, whipped off
a 6 m storm surge that inundated 20,000 hectares of agricultural land, tens of
villages, and severely affected thousands of families of coastal Orissa. A strong cyclone with wind speeds of 300 km
per hour could easily create a storm surge of 10 m high. Should a surge of this magnitude hit the
coastal
So confident was Achyutananda of his prophecies that in one of his writings he says:
‘Parbata sikhare phutiba kain,
Achyutara katha taliba nahin’;
which when translated into English would read:
Water lilies will bloom atop the mountains blue,
Mark Achyuta’s words, for they will come true. (Translation ND).
However, astounding this prediction may appear, it is not all that far fetched. Let me explain, very briefly, how this could eventuate. The very site of the Jagannath temple, Neelachala, which as explained earlier in the text was once an impressive mountain, is barely above sea level thanks to the rising sea. As the sea rises even higher, places along the coast which were once hill tops during the last ice age, will be water logged ponds where lilies will bloom.
Achyutananda’s
confident prophecies scare me, and give me the feeling that the people of the
east coast of
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