Geoffrey Lean in The Independent claims:

Rising seas, caused by global warming, have for the first time washed an inhabited island off the face of the Earth. The obliteration of Lohachara island, in India’s part of the Sundarbans where the Ganges and the Brahmaputra rivers empty into the Bay of Bengal, marks the moment when one of the most apocalyptic predictions of environmentalists and climate scientists has started coming true. ..

Two-thirds of nearby populated island Ghoramara has also been permanently inundated. Dr Sugata Hazra, director of the university’s School of Oceanographic Studies, says “it is only a matter of some years” before it is swallowed up too.

This story doesn’t seem right. While global warming has increased sea levels, the increase to date has only been a couple of centimetres, which doesn’t seem enough to submerge an island. Let’s do some checking.

i-992bc141dcd7fa3e9a49dfc8f260e768-lohachara.jpg

First, you can confirm that Lohachara island really has vanished by using Google maps. I’ve superimposed the map view with the satellite view, so you can see that where the map shows the island, in the satellite view there is only water.

Second, when did the island vanish? India’s Telegraph reports:

Shamila and her mother never thought the sea would completely devour their tiny island of Lohachara in the Sundarbans. And then one day, it did. The family of four was forced to pack its modest belongings and head for Sagar, the largest island in west Sundarbans. In the late 1990s, more such families followed suit. …

The team first noticed that the islands were vanishing while working on a Government of India funded project in 2001. The government census was still showing a population of 5,000 in Ghorama, one of the fast submerging islands. “But we could not find the island in the satellite images. Official records showed 102 islands in the estuary, but we found only 100. Where had the other two gone,” says Hazra of the basic premise which stoked his team’s curiosity.

So some of it was still there in the late 1990s, but it was all gone in 2001.

Third, why did it vanish? According to the Indian Express:

Prof Sugata Hazra, director, School of Oceanographic Studies, said: “A preliminary survey reveals that around 7,000 people have been displaced from their original habitat in Sunderbans over the last 30 years. They have turned into environmental refugees due to the sea-level rise, coastal erosion, cyclone and coastal flooding.”

The migrants, now living in various refugee colonies, are just an indication of what is in store for the world-renowned mangrove islands, the scientists warned.

So sea level rise was just one of the factors. And sea level rise can also be caused by land sinking as well as the ocean rising. I found a scientific paper on the topic by Gopinath and Seralathan in Environmental Geology. (Yes, the same journal that published Khilyuk and Chilingar‘s tripe.)

Gopinath and Seralathan studied Sagar island which is just 1 km from where Lohachara used to be, so their conclusions apply to Lohachara as well. They found that reduced flows in the river were causing sediments to be deposited further upstream instead of replacing erosion at Sagar island. Furthermore, the major cause of the relative sea level rise which made for more erosion, was land subsidence, not global warming.

So it is wrong to blame Global Warming for the disappearance of Lohachara island. This isn’t much comfort for people living on the other islands in the Sundarbans, since Global Warmingis likely to produce significant sea level rises in the future and Lohachara demonstrates that these islands are vulnerable to small rises in sea level.

Comments

  1. #1 Meyrick Kirby
    December 31, 2006

    Err, if Gopinath and Seralathan(2005) was published in Environmental Geology, can it really be trusted?

  2. #2 JB
    December 31, 2006

    These are the kind of stories that the denialists jump all over… and use to make sweeping generalizations about environmentalists and environmental scientists alike.

    The error was clearly the journalist’s for relying on a single source… kind of like concluding that “climate scientists have oversold the science of global warming” based on a conversation with one (or just a few) climate scientists.

  3. #3 coby
    December 31, 2006

    I thought that sea levels have risen 10-20cm over the last century.

    Not commenting directly on this case which I think Tim has described fairly, but it is a mistake to think that land at 1m above sea level will only be submerged when the ocean rises 1.01m There is also erosion to consider as high tide lines advance and water tables rise affecting vegetation and earth.

    I would imagine that subsidence could be caused indirectly by SLR in a case similar to this particular island where sediment deposition patterns were altered by higher sea levels.

  4. #4 coby
    December 31, 2006
  5. #5 oneoffmanmental
    December 31, 2006

    I believe the article’s author is a friend of a UK radical environmental group that I know and keep having a go at about their inaccuracies, so I doubt a climate scientist was even contacted in this case.

  6. #6 bigTom
    December 31, 2006

    I presume this estuary doesn’t have high tides, or large waves, or
    large water level fluctuations due to river flow etc. Given the roughly 20cm of sea-level rise, and XX of subsidence, you could ascribe fractional blame to GW. Kind of like New Orleans, subsidence is greater than sea-level rise, but the effects of both add up.
    Alaska had to resettle a coastal village, largely because loss of sea ice, meant that waves could erode the land edge, which had become more vulnerable due to thawing.

  7. #7 Adolf powell
    December 31, 2006

    Hi all
    Can anything in Wikipedia be trusted?
    Yours Adolf

  8. #8 coby
    December 31, 2006

    Turns out wikipedia is just about as reliable as encyclodedia brittanica

  9. #9 Ian Gould
    January 1, 2007

    Wikipedia is as trustworthy as its sources and its a handy compendium.

    In other words, look there first and follow the links.

    Coby – considering that large pieces of Wikipedia are copied from old editions of EB that are now in the public domain that’s hardly surprising.

  10. #10 Ian Gould
    January 1, 2007

    In this case Wikipedia’s source appears to be the IPPC’s 3rd TAR.

    While I can’t find that particular graph in the TAR, this section tells the same basic story:

    http://www.grida.no/climate/ipcc_tar/wg1/425.htm

  11. #11 moptop
    January 1, 2007

    Thank you for this. One of the reason many of us are skeptics is because of obvious overstatements of the current effects of GHG that do not pass the smell test.

    For example:

    “I thought that sea levels have risen 10-20cm over the last century.” — coby.

    This is probably true, though I don’t know the exact number, I do know that sea levels have been rising for millenia, since the last ice age ended. There is all kinds of evidence for this if you doubt it, you can think about the former land bridge to the Americas from Asia that has since been flooded by rising sea levels. Natural sea level rise may account for four feet or so since the founding of New Orleans.

    The question is, and commenters here seem to have a hard time with this, how much of that rise is due to AGW?

    Using the whole number is either dishonest or risibly misinformed. I notice that Mr Lambert does not do this, his fundimental honesty is one of the reasons I keep coming back here.

    Now if we could just talk about those refugees from Tuvalu?

    Here is a story on “Indymedia” from last week:

    Climate Change: Rising seas create 70,000 refugees.
    http://www.indybay.org/newsitems/2006/12/27/18341209.php

    These are the kind of stories that set off BS detectors in thinking people and make AGW a harder sell than it should be. Of course, they also make the threat less dramatic, but it really should be climate scientists, not expert politician and propagandist Al Gore, who are leading the debate.

  12. #12 Tim Lambert
    January 1, 2007

    moptop, sea levels at Tuvalu are rising and people are leaving the island as a result. Maybe they are wrong to be concerned, but maybe they know more about the situation than you do?

  13. #13 tim.ameigh
    January 1, 2007

    The question isn’t that sea levels are rising, and that Tuvalu is at risk, the question is, can you blame AGW for it.

    Can these people properly be termed “Climate Refugees”, with all of the implications that AGW is the root cause?

    What about these people?
    http://www.archaeologyonline.net/artifacts/gulf-of-cambay.html

    You know, the ones whose city was submerged thousands of years ago by rising sea levels? If you can call either of them “Climate refugees”, then you have stretched the word to the point of meaninglessness.

    This does not mean that Tuvalu doesn’t deserve our help, it is just that neither can it be justified to make them poster children for AGW on the basis of, in your words,

    “the increase to date has only been a couple of centimetres, which doesn’t seem enough o submerge an island.”

  14. #14 llewelly
    January 1, 2007

    moptop said:

    “I thought that sea levels have risen 10-20cm over the last century.” — coby.

    This is probably true, though I don’t know the exact number, I do know that sea levels have been rising for millenia, since the last ice age ended. There is all kinds of evidence for this if you doubt it, you can think about the former land bridge to the Americas from Asia that has since been flooded by rising sea levels. Natural sea level rise may account for four feet or so since the founding of New Orleans.

    New Orleans was founded in about 1718. Guesstimating from the wikipedia graph of Holocene Sea Level I suspect the last time sea level was 4 feet lower than now was over 2500 years ago. New Orleans is strongly affected by subsidence – up to 2.0m in some places. As a rule of thumb, when you hear a river delta island is sinking, you should suspect subsidence is a primary cause. ( Unfortunately, I think we’ll continue to see news stories about sinking river delta islands blame global warming’s 0.3mm/yr to 0.8mm/yr contribution, despite subsidence contributing (for example) 6.9mm/yr . That’s why places like RC and Deltoid spend as much effort countering sensationalist news stories as they do countering denialist woo. )

    With respect to Wikipedia – one should always check the history, and the discussion, as these can often reveal incompleteness, vandalism, ongoing controversies, or simply that the article is no longer maintained. Note, Brittanica has no comparable functionality – the record of why a given article changed is occasionally quite important, but Brittanica conceals such data from its users.

  15. #15 llewelly
    January 1, 2007

    I mistakenly said:

    … blame global warming’s 0.3mm/yr to 0.8mm/yr contribution …

    Sea level rise over the last 100 years has been estimated at 1.0mm/yr to 2.0mm/yr . I misread a statement about the acceleration of sea level rise over the 20th century, thinking it was a statement about global warming’s contribution. I apologize for any confusion.

  16. #16 moptop
    January 1, 2007

    llewelly,

    You sure got me on the founding of New Orleans! I had assumed it was contemporanious with the founding of New France, but it turns out the have happened later in the 17th century, La Salle got there about 50 years before the “official” founding of the city. I just don’t get what it proves about AGW. What argument are you specifically trying to win?

    Given your two posts, could you please give me a simple sentence which states the “AGW” contribution to sea level rise as you understand it? I don’t see it there.

    If I look at the temperature history over the past several thousand years, oddly enough, it looks nothing like a hockey stick.

    Katrine Krogh Andersen, Peter Ditlevsen and Jørgen Peder Steffensen,
    Department of Geophysics, NBIfAFG, University of Copenhagen

    http://www.gfy.ku.dk/~kka/icecores_palaeoclimate.pdf

    But I can see where glacial runnoff is not a constant process given the natural variability of the climate.

    Or has the work on Greenland ice cores cited above been shown to be incorrect somewhere?

  17. #17 moptop
    January 1, 2007

    I am guilty of substituting order of magnitude “feet” for 10 to 20 CM. This was error in thinking on my part which I thank you for pointing out. Half a foot would be much closer. I should have said 2 feet, not four.

  18. #18 Ian Gould
    January 1, 2007

    From the IPCC document I linked to earlier:

    “Comparison of the rate of sea level rise over the last 100 years (1.0 to 2.0 mm/yr) with the geological rate over the last two millennia (0.1 to 0.2 mm/yr; Section 11.3.1) implies a comparatively recent acceleration in the rate of sea level rise.”

    So the IPCC is saying that in the last century the rate of increase has increased by 0.8 to 1.9 millimetres per year.

    Is there any viable alternative theory to AGW on the table to explain this increase?

    1 millimetre per year sounds trivial but you have to look at the impact of even a centimetre or two on king tides and storm surges in low-lying areas – it’s the maxima that matter not the averages.

    Another key point someone touched on briefly is hydrology. Coral atolls typically depend on a thin level of fresh groundwater sitting above layers of saline groundwater.

    Long before most of these islands are actually submerged, rising sea levels will probably make them uninhabitable due to saline contamination of the ground water.

    Most inhabited coral atolls draw their drinking water from these ground water resources and rising populations and water demand on many of them are also leading to salt water
    intrusion, this is going to make it difficult to separate out the impacts of AGW and population growth.

  19. #19 observer
    January 2, 2007

    Seems that Tim Blair beat you to it on exposing this scam.

  20. #20 llewelly
    January 2, 2007

    moptop again:

    If I look at the temperature history over the past several thousand years, oddly enough, it looks nothing like a hockey stick.

    Katrine Krogh Andersen, Peter Ditlevsen and Jorgen Peder Steffensen, Department of Geophysics, NBIfAFG, University of Copenhagen

    http://www.gfy.ku.dk/~kka/icecores_palaeoclimate.pdf

    The hockey stick was composed of many proxies of many different sorts, producing an estimate for the average of the whole of the Northern Hemisphere. The paper you link to is about one kind of proxy – ice cores. A small number of proxies is much more likely to be affected by local climate variations, and is thus less likely to produce long stretches of relatively little variation. Perhaps more importantly – snow falling on a glacial ridge does not become ice instantly – it takes decades at some sites. As a result, not all the ice core proxies capture the dramatic AGW rise of the last ~30 years. Nonetheless … examine figure 3 on page 5, which clearly displays a very sharp rise in the 1900-2000 area.

  21. #21 mgr
    January 2, 2007

    I think there is a problem here. There is a facile global warming argument that Lohachara’s inundation is due to sea level rise alone; and there is the more complex argument associated with the change in river flow and sedimentation. Further assessment is needed.

    A deltaic island is a far more complex setting to test the assertion that islands may be inundated by sea level rise, and it is the coral atolls and emergent sea mounts that will be the critical test of the simplistic scenario. The entire history of Holocene coastal mapping has been an interplay of isostacy and recession (just look at past maps of Scandinavian coast).

    Mike

  22. #22 hippie with a pistol
    January 4, 2007

    Mr Sugata Hazra, the source for the latest news on Lohachara Island, and his staff presented a paper to the Asian Conference on Remote Sensing IN 2001 entitled, “Assessment of Landuse/Landcover Dynamics and Shoreline Changes of Sagar Island Through Remote Sensing.”

    http://www.crisp.nus.edu.sg/~acrs2001/pdf/172HAZRA.pdf

    The submerged island of Lohachara is just northwest of Sagar Island. Interestingly, in this paper he doesn’t claim global warming to be the explanation for the shoreline changes on Sagar Island. Hazra and his staff have found that the rate of erosion increased greater than the rate of accretion. The paper explains that the islands in this estuary experienced a stable existence when the freshwater inflow from the Hoogly was of high intensity until the Ganges shifted course due to a recent tectonic tilt. Since then the islands within the estuary are experiencing a hydrodynamic imbalance. It is also noted that the sea level rise is 2.36 mm/yr…less than the global average of approximately 3mm/yr…the closest he comes to attributing the cause soley on global warming.

    Now let’s compare that rate of sea level rise to the rate measured by the Colorado Center for Astrodynamics Research at the University of Colorado. For the Bay of Bengal the average rise in sea level is 2.825mm since late 1992 (see inverted barometer adjustment)

    http://sealevel.colorado.edu/results.html

    What should also be noted, that you won’t hear from global warming advocates like Al Gore, is that this estuary is on the Faridpur Trough, adjacent to the Calcutta-Mymensingh Hinge. The Faridpur Trough is part of the subsiding Bengal Basin. It is subsiding at a rate of at least 2 cm/yr!!!!

    http://banglapedia.org/HT/S_0575.HTM

    And for some context take a look at long-term sea level changes:

    http://www.nio.org/aroundus/Sagar/sea_level_changes.jsp

    But enough of that. Let’s go back to Mr Hazra and his gross errors, exaggerated facts, or just plain lies. You decide. Take a look at Figure 2 in the paper presented at the Asian Conference on Remote Sensing. The change in shoreline extents has been demarcated. In Figure 3 he shows a graph of areal change over time. The graph shows a reduction of areal extents by a little over 12%, or 33.62 km sq. (The paper indicates 30 km sq). But does the Figure 2 map look like there has been that great of a change? I don’t think so. Well, I planimetered the shorelines in his figure 2 and came up with some interesting calculations. For the 1999 boundary I calculated an area similar to his – 243 km sq (compared to his 240). But for the 1969 boundary the area is not 273 km sq as Hazra’s paper claims. It’s approximately 255 km sq – a difference of 12 km sq, or a change of about 5%!!!!

    Mr Hazra, you claim Sagar Island has lost 30 km sq in 30 years, but your map shows that the island has lost 12 km sq.

    But it gets worse for Mr Hazra. Let’s refer to maps prepared by the US Army Map Service in compiled in 1954, specifically sheet NF-45-11 which shows Sagar Island.

    http://www.lib.utexas.edu/maps/ams/india/

    I planimetered Sagar Island calculating an area of 247 km sq, or 61,206 acres. Mr Hazra’s area calculation for Sagar Island in 1999 is 240 km sq. Results? The area of Sagar Island has reduced in size by 7 km sq, or 930 acres.

    But what does the recent news story tell us? Remember, Mr Hazra is the source. Here it is:

    Refugees from the vanished Lohachara island and the disappearing Ghoramara island have fled to Sagar, but this island has already lost 7,500 acres of land to the sea.

    Uh, Mr Hazra, your hoax has been exposed.

    Mr Hazra repeats the error, exaggeration or lie again:

    http://www.omantribune.com/index.php?page=news&id=22798&heading=India

    Pointing out that the Sagar island, the largest among the 100 odd ones in the deltaic region, has already lost nearly 30sq km area in last three decades, he said that apart from the factors mentioned earlier, increasing population, rise in salinity in water, siltation at jetties and navigational channels were also responsible for the disastrous consequences.

    Mr Hazra has submitted his latest study to the IPCC for the next report on climate change. He has not released it or the data to the public. I wonder why? You got something to hide, Mr Hazra?

  23. #23 mgr
    January 10, 2007

    Hippie with a pistol: just what are you saying? Your argument, analysis and conclusions are not compelling; and are more suited to a bathroom and seeing what sticks.

    A. Your methods are suspect.

    1.)Map and aerial photocomparison–you do not employ the same maps as Ghosh, Bhandari, and Hazra employ. Note that they use the Survey of India toposheets, not the US Army map you employ.
    2.)Planimeter measurements are notoriously suspect–the border between Spain and Portugal has been variously estimated by either government, and depending on the circumference of the wheel and whether the outside, inside, or middle of the line is measured, but the difference has been on the order of a thousand miles
    3.)It is not evident that areal estimates were obtained by planimeter, but may have been field truthed by survey in the article you cite.
    4.)Estimates of land loss depend on what time of day an aerial photograph is taken. Periods of low flow/low tide will have a greater surface area than those of high flow/high tide. The same can be said of a map that depends on aerial data (highly likely with your DOD map)
    5.)You cherry picked the subsidence data–it ranges from a high of 2.4 cm to a low of 0.065 cm as a regional average at Dhaka, and appears to conform to a south west/north east gradient as one approached the delta (e.g. the lower values of subsidence are likely to better estimate local variables at the island)

    B. You are logically inconsistent. You argue that subsidence in the area should be of a higher magnitude, yet make an argument that given Ghosh, Bhandari, and Hazra’s data, subsidence is less than they estimate. Under these constraints, anything would be a lie.

    C. The analysis of the Sagar Island is not in a vacuum, but is consistent with observed regression of land in Bangladesh. I am aware of analysis of this issue from as far back as 1984 that employed similar aerial photo comparison and analysis.

    D.The open question is what data Hazra is bringing (since he is not the principal author on the article you provide), since this paper would suggest baseline against which he may have other information. If he has identified historic rates of subsidence at the island, such as from carbon dated submerged mangrove wood , and this is inconsistent with current rates of sea level progression, there may be something. If it is an example of the class of problems to be expected, and is a model for planning and preparation, that is something else.

    Mike

  24. #24 Tim Lambert
    January 10, 2007

    I should note in addition that Gopinath and Seralathan got similar results to Ghosh Bandari and Hazra.

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