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 impressi