I would second the idea. The rise in sea level has already submerged two islands
in the Indian Sundarbans, and is swallowing up large parts of the remaining
islands. Thusands of people in these thickly populated islands have been
rendered environmental refugees, and concerns are that half a million will be
homeless by 2020.

Rina Mukherji

Kolkata

"Arshad H. Abbasi" <arshadhabbasi@...> wrote:

Dear Pankaj and Lal Mohan
Would you like to arrange a seminar or technical debate over the serious issue
of sea level rise? Sea level rise not only eroding; and but also cause cyclone,
tsunamis etc.
The need is start campaign against root -causes of sea level rise and one of
them is melting of glaciers.
I hope you will consider my proposal


lal mohan <samuelji2003@...> wrote:
Dear Pankaj,

Iam concerned with the sea level rise. In India along the Kanyakumari coast.This
sea level rise is evident as the sea erosion has already eaten some villages.
The Govt is trying to stop the advance of sea by erecting sea walls. As a
environmentalist I know it is a futile attempt. On the other side the Govt is
inviting foreign investments for automobile industry and many foreign companies
life Hyndai,Fiat and other Japaneese firms are coming to India resulting in more
cars and more carbon emission.
We fail to see the end result of advancement of the sea as a dangerous sign of
impending danger.

Yours Sincerely,

(R.S.LAL MOHAN)

Pankaj Andaman <psekhsaria@...> wrote:
Huge sea level rises are coming – unless we act now
NewScientist.com, 25 July 2007

by JAMES HANSEN
James Hansen heads NASA's Goddard Institute for Space Studies in New
York. A physicist and astronomer by training, he began his career
studying the clouds on Venus. Since the late 1970s he has been studying
and modelling the human impact on Earth's climate, and has published
more than 100 papers. He entered the public spotlight in the 1980s with
his outspoken testimony to congressional committees on climate change.
Last year he made headlines when he spoke out against attempts by the US
administration to gag climate scientists.

http://environment.newscientist.com/article.ns?id=mg19526141.600&feedId=climate-\
change_rss20

I find it almost inconceivable that "business as usual" climate change
will not result in a rise in sea level measured in metres within a
century. Am I the only scientist who thinks so?

Last year I testified in a case brought by car manufacturers to
challenge California's new laws on vehicle emissions. Under questioning
from the lawyer, I conceded that I was not a glaciologist. The lawyer
then asked me to identify glaciologists who agreed publicly with my
assertion that sea level is likely to rise more than a metre this
century if greenhouse gas emissions continue to grow: "Name one!"

I could not, at that moment. I was dismayed, because in conversations
and email exchanges with relevant scientists I sensed a deep concern
about the stability of ice sheets in the face of "business as usual"
global warming scenarios, which assume that emissions of greenhouse
gases will continue to increase. Why might scientists be reticent to
express concerns about something so important?

I suspect it is because of what I call the "John Mercer effect". In
1978, when global warming was beginning to get attention from government
agencies, Mercer suggested that global warming could lead to disastrous
disintegration of the West Antarctic ice sheet. Although it was not
obvious who was right on the science, I noticed that researchers who
suggested that his paper was alarmist were regarded as more authoritative.

It seems to me that scientists downplaying the dangers of climate change
fare better when it comes to getting funding. Drawing attention to the
dangers of global warming may or may not have helped increase funding
for the relevant scientific areas, but it surely did not help
individuals like Mercer who stuck their heads out.

I can vouch for that from my own experience. After I published a paper
in 1981 that described the likely effects of fossil fuel use, the US
Department of Energy reversed a decision to fund my group's research,
specifically criticising aspects of that paper.

I believe there is pressure on scientists to be conservative. Caveats
are essential to science. They are born in scepticism, and scepticism is
at the heart of the scientific method and discovery. However, in a case
such as ice sheet instability and sea level rise, excessive caution also
holds dangers. "Scientific reticence" can hinder communication with the
public about the dangers of global warming. We may rue reticence if it
means no action is taken until it is too late to prevent future disasters.

So why do I think a sea level rise of metres would be a near certainty
if greenhouse gas emissions keep increasing? Because while the growth of
great ice sheets takes millennia, the disintegration of ice sheets is a
wet process that can proceed rapidly.

Sea level is already rising at a moderate rate. In the past decade, it
increased by 3 centimetres, about double the average rate during the
preceding century. The rate of sea level rise over the 20th century was
itself probably greater than the rate in the prior millennium, and this
is due at least in part to human activity. About half of the increase is
accounted for by thermal expansion of ocean water as a result of global
warming. Melting mountain glaciers worldwide are responsible for several
centimetres of the increase.
"While the growth of great ice sheets takes millennia, they can
disintegrate rapidly"

Greenland and Antarctica are also contributing to the rise in recent
years. Gravity measurements by the GRACE satellites have recently shown
that the ice sheets of Greenland and West Antarctica are each losing
about 150 cubic kilometres of ice per year. Spread over the oceans, this
is close to 1 millimetre a year, or 10 centimetres per century.
Runaway collapse

The current rate of sea level change is not without consequences.
However, the primary issue is whether global warming will reach a level
such that ice sheets begin to disintegrate in a rapid, non-linear
fashion on West Antarctica, Greenland or both. Once well under way, such
a collapse might be impossible to stop, because there are multiple
positive feedbacks. In that event, a sea level rise of several metres at
least would be expected.

As an example, let us say that ice sheet melting adds 1 centimetre to
sea level for the decade 2005 to 2015, and that this doubles each decade
until the West Antarctic ice sheet is largely depleted. This would yield
a rise in sea level of more than 5 metres by 2095.

Of course, I cannot prove that my choice of a 10-year doubling time is
accurate but I'd bet $1000 to a doughnut that it provides a far better
estimate of the ice sheet's contribution to sea level rise than a linear
response. In my opinion, if the world warms by 2 °C to 3 °C, such
massive sea level rise is inevitable, and a substantial fraction of the
rise would occur within a century. Business-as-usual global warming
would almost surely send the planet beyond a tipping point, guaranteeing
a disastrous degree of sea level rise.

Although some ice sheet experts believe that the ice sheets are more
stable, I believe that their view is partly based on the faulty
assumption that the Earth has been as much as 2 °C warmer in previous
interglacial periods, when the sea level was at most a few metres higher
than at present. There is strong evidence that the Earth now is within 1
°C of its highest temperature in the past million years. Oxygen isotopes
in the deep-ocean fossil plankton known as foraminifera reveal that the
Earth was last 2 °C to 3 °C warmer around 3 million years ago, with
carbon dioxide levels of perhaps 350 to 450 parts per million. It was a
dramatically different planet then, with no Arctic sea ice in the warm
seasons and sea level about 25 metres higher, give or take 10 metres.

There is not a sufficiently widespread appreciation of the implications
of putting back into the air a large fraction of the carbon stored in
the ground over epochs of geologic time. The climate forcing caused by
these greenhouse gases would dwarf the climate forcing for any time in
the past several hundred thousand years - the period for which accurate
records of atmospheric composition are available from ice cores.

Models based on the business-as-usual scenarios of the Intergovernmental
Panel on Climate Change (IPCC) predict a global warming of at least 3 °C
by the end of this century. What many people do not realise is that
these models generally include only fast feedback processes: changes in
sea ice, clouds, water vapour and aerosols. Actual global warming would
be greater as slow feedbacks come into play: increased vegetation at
high latitudes, ice sheet shrinkage and further greenhouse gas emissions
from the land and sea in response to global warming.

The IPCC's latest projection for sea level rise this century is 18 to 59
centimetres. Though it explicitly notes that it was unable to include
possible dynamical responses of the ice sheets in its calculations, the
provision of such specific numbers encourages a predictable public
belief that the projected sea level change is moderate, and indeed
smaller than in the previous IPCC report. There have been numerous media
reports of "reduced" predictions of sea level rise, and commentators
have denigrated suggestions that business-as-usual emissions may cause a
sea level rise measured in metres. However, if these IPCC numbers are
taken as predictions of actual sea level rise, as they have been by the
public, they imply that the ice sheets can miraculously survive a
business-as-usual climate forcing assault for a millennium or longer.

There are glaciologists who anticipate such long response times, because
their ice sheet models have been designed to match past climate changes.
However, work by my group shows that the typical 6000-year timescale for
ice sheet disintegration in the past reflects the gradual changes in
Earth's orbit that drove climate changes at the time, rather than any
inherent limit for how long it takes ice sheets to disintegrate.

Indeed, the palaeoclimate record contains numerous examples of ice
sheets yielding sea level rises of several metres per century when
forcings were smaller than that of the business-as-usual scenario. For
example, about 14,000 years ago, sea level rose approximately 20 metres
in 400 years, or about 1 metre every 20 years.

There is growing evidence that the global warming already under way
could bring a comparably rapid rise in sea level. The process begins
with human-made greenhouse gases, which cause the atmosphere to be more
opaque to infrared radiation, thus decreasing radiation of heat to
space. As a result, the Earth is gaining more heat than it is losing:
currently 0.5 to 1 watts per square metre. This planetary energy
imbalance is sufficient to melt ice corresponding to 1 metre of sea
level rise per decade, if the extra energy were used entirely for that
purpose - and the energy imbalance could double if emissions keep growing.

So where is the extra energy going? A small part of it is warming the
atmosphere and thus contributing to one key feedback on the ice sheets:
the "albedo flip" that occurs when snow and ice begin to melt.
Snow-covered ice reflects back to space most of the sunlight striking
it, but as warming air causes melting on the surface, the darker ice
absorbs much more solar energy. This increases the planetary energy
imbalance and can lead to more melting. Most of the resulting meltwater
burrows through the ice sheet, lubricating its base and speeding up the
discharge of icebergs to the ocean.

The area with summer melt on Greenland has increased from around 450,000
square kilometres when satellite observations began in 1979 to more than
600,000 square kilometres in 2002. Seismometers around the world have
detected an increasing number of earthquakes on Greenland near the
outlets of major ice streams. The earthquakes are an indication that
large pieces of the ice sheet lurch forward and then grind to a halt
because of friction with the ground. The number of these "ice quakes"
doubled between 1993 and the late 1990s, and it has since doubled again.
It is not yet clear whether the quake number is proportional to ice
loss, but the rapid increase is cause for concern about the long-term
stability of the ice sheet.

Additional global warming of 2 °C to 3 °C is expected to cause local
warming of about 5 °C over Greenland. This would spread summer melt over
practically the entire ice sheet and considerably lengthen the melt
season. In my opinion it is inconceivable that the ice sheet could
withstand such increased meltwater for long before starting to
disintegrate rapidly, but it is very difficult to predict when such a
period of large, rapid change would begin.

Summer melt on West Antarctica has received less attention than on
Greenland, but it is more important. The West Antarctic ice sheet, which
rests on bedrock far below sea level, is more vulnerable as it is being
attacked from below by warming ocean water, as well as from above by a
warming atmosphere. Satellite observations reveal increasing areas of
summer melt on the West Antarctic ice sheet, and also a longer melt season.
Warmer oceans

The warming atmosphere and increased absorption of sunlight are not the
only factors that will increase surface melt. If there is a significant
loss of ice, the surfaces of the ice sheets will be at lower altitudes,
where the air is warmer, causing additional melt: another positive feedback.

Most of the excess energy due to the planetary imbalance is going into
the ocean rather than the atmosphere, because it takes about 1000 times
as much energy to heat the oceans by 1 °C as it does to heat the
atmosphere as much. The acceleration of ice sheet disintegration depends
on how much of the extra ocean heat is transferred to the ice.

This transfer can occur in two main ways: by the speeding up of glaciers
resulting in more ice being discharged into the oceans, and by direct
transfer of heat from the water underneath and against fringing ice
shelves. Since fringing ice shelves float on water, their melting does
not raise sea level directly. However, ice shelves hold back the ice
sheets resting on land or on the seabed, so as the ice shelves melt or
break up, the ice streams draining the ice sheets accelerate, providing
another positive feedback effect.

An example was recently seen on the Antarctic Peninsula. The combined
effect of surface melt and ice shelf thinning from below led to the
sudden collapse of the Larsen B ice shelf, which was followed by the
acceleration of glacial tributaries far inland.

Positive feedback from loss of buttressing ice shelves will influence
some Greenland ice streams, but the West Antarctic ice sheet will be
affected much more. The local warming and melt that preceded the Larsen
B collapse was only a fraction of the expected warming in the West
Antarctic under business-as-usual scenarios. In fact, observations show
the ocean around West Antarctica is already warming, ice shelves are
thinning by several metres per year, and glaciers are discharging more
icebergs.

There are also some negative feedbacks, in the short term at least. As
the discharge of ice increases, regional cooling by the icebergs will be
significant. This cooling can lead to increased sea ice and cloud cover,
and thus increased reflection of sunlight. However, cooling of the ocean
surface by melting ice also reduces heat radiation from the water
surface. This increases the planetary energy imbalance, thus supplying
additional energy for ice melt. Models confirm that the cooling effect
of melting ice is temporary and that there will be a net increase in
ocean heat uptake around West Antarctica and Greenland as greenhouse
gases increase.

Another negative feedback is increasing snowfall on ice sheet interiors,
because of the higher moisture content of the warming atmosphere. Some
models predict that ice sheets will grow overall with global warming,
but those models do not include realistic processes of ice sheet
disintegration. Palaeoclimate data confirms the common-sense expectation
that the net effect is for ice sheets to shrink as the world warms, as
the GRACE satellites show is happening already.

The findings in the Antarctic are the most disconcerting. Warming there
has been limited in recent decades, in part due to the effects of ozone
depletion. The fact that West Antarctica is losing mass at a significant
rate suggests that the thinning ice shelves are already beginning to
affect ice discharge rates.

So far, warming of the ocean surface around Antarctica has been small
compared with the rest of the world, as models predict, but that limited
warming is expected to increase. The detection of recent, increasing
summer surface melt on West Antarctica raises the danger that feedbacks
among these processes could lead to non-linear growth of ice discharge
from Antarctica.

This problem is urgent. The non-linear response could easily run out of
control, both because of the positive feedbacks and because of inertias
in the system.

Ocean warming and thus melting of ice shelves will continue even if CO2
levels are stabilised, because the ocean response time is long and the
temperature at depth is far from equilibrium for current forcing. Ice
sheets also have inertia and are far from equilibrium. There is also
inertia in human systems: even if it is decided that changes must be
made, it may take decades to replace infrastructure.

The threat of large sea level change is a principal element in my
argument that the global community must aim to restrict any further
global warming to less than 1 °C above the temperature in 2000. This
implies a CO2 limit of about 450 parts per million or less. Such
scenarios require almost immediate changes to get energy and greenhouse
gas emissions onto a fundamentally different path.

Is my perspective on this problem really so different than that of other
relevant members of the scientific community? Based on interactions with
others, I conclude that there is not such a great gap. The apparent
differences may arise partly from a natural reluctance to speak out.

Reticence is fine for the IPCC. Individual scientists also can choose to
stay within a comfort zone, and not worry that they may say something
that proves to be slightly wrong. But perhaps we should consider our
legacy from a broader perspective. Do we not know enough to say more?
Using the fact that a glacier on Greenland slowed after speeding up as
"proof" that reticence is appropriate is little different from the
common misconception that a cold weather snap disproves global warming.

The broader picture strongly indicates that ice sheets will respond in a
non-linear fashion to global warming - and are already beginning to do
so. There is enough information now, in my opinion, to make it a near
certainty that business-as-usual scenarios will lead to disastrous
multi-metre sea level rise on the century time scale.

This article is based on a paper in the open-access journal
Environmental Research Letters (DOI: 10.1088/1748-9326/2/2/024002)

From issue 2614 of New Scientist magazine, 25 July 2007, page 30-34

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