Bangladesh and Sea Level Rise

You’ve all heard about the horrible tragedy in Bangladesh, still unfolding. Not to distract from that event, or diminish its importance, I thought it would be interesting to have a look at that low lying country in relation to long term sea level rise caused by climate change. I am making no claim here about the maximum rate of sea level rise or about the timing of sea level rise. But the truth is, there have been times in the past when there was virtually no year round ice (glaciers) anywhere on this planet, and sea levels were much higher than they are now. During a time period not too different from the present (probably not as warm, or just about the same) sea levels were several meters (maybe about 6 meters) higher than they are now, suggesting that even under current conditions a lot of the ice in Greenland and Antarctica could melt. In other words, there is an argument that even if we curtail global warming now and keep things at their current somewhat warmed up level ice may continue to melt enough to raise the sea by meters. If we continue to warm the atmosphere and the oceans, the total sea level rise could be much, much higher.

Using the interactive map here, let’s look at Dhaka, the site of the recent and ongoing tragedy in Bangladesh. This is appropriate because it is the first world thirst for goods and luxury that produces both sweat shops like the one that just collapsed, killing hundreds of workers, and that produces global warming that will also produce catastrophic sea level rise.

Here’s a map of the area now, showing the local terrain:

Dhaka, Bangladesh.

Dhaka, Bangladesh.

If the entire Greenland Ice Sheet melted (but nothing else), or if a bunch of Greenland and a bunch of Antarctica melted, to produce about 7 meters of sea level rise, this is what the map would look like:

Screen Shot 2013-04-29 at 8.42.56 AM

This is not what the region would look like, actually. The sediment here is all soft delta material what would be eroded away horizontally in no time. Another way to think about this is that if the sea went up just a meter or two, this entire region would probably be eaten away by horizontal erosion very quickly. Anyway, let’s add some more water and see what this first approximation would look like. Imagine if the West Antarctic and Greenland ice sheets both contributed maximally to sea level rise. This would be the minimal result:

Screen Shot 2013-04-29 at 8.43.17 AM

If all the glacial ice in the world melted, and sea levels rose to the maximum height they’ve ever been, our closeup look of the region would look like this:

Screen Shot 2013-04-29 at 8.43.32 AM

As you probably know, Bangladesh is one of the lowest elevation larger countries in the world. In fact, it seems like Bangladesh is defined almost entirely by its topography; Bangladesh is the delta. If we take the same maximal sea level rise as in the last graph, and step back a ways to see the effect at large scale, this is what we get:

They would have to call Bangladesh something else.

They would have to call Bangladesh something else.

By the way, there’s a cool book coming out on the topic, Rising Seas: Past, Present, Future.

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Photo Credit: joiseyshowaa via Compfight cc

Comments

  1. […] with small populations but also heavily populated coastal regions, such as Kolkata, India and Dhaka, […]

  2. #2 Endi
    new york city, ny, united states
    November 9, 2014

    How were you able to get the maps of the predicted water rise over Dhaka?

  3. #3 Greg Laden
    November 9, 2014
  4. #4 Astrostevo
    November 10, 2014

    Scary stuff especially when you realise the maps and models are mostly erring on the cautious side and likely to be underestimates given the observations show some things eg. Arctic sea ice melting faster than predicted.

    We’re apparently already past the tipping point for West Antarctica melting but this story :

    http://www.abc.net.au/science/articles/2014/05/13/4003536.htm

    Which arguably should have been the most important and discussed news item of the year seems to have gone largely unnoticed because its isn’t an instant thing. Short term thinking strikes again.

    Of course for a lot of people the same exercise here performed with Florida or New York or London instead of Bangladesh may have more impact.

  5. #5 Astrostevo
    November 10, 2014

    PS. One thing to note here that I couldn’t see mentioned in the article but should have been is the timescale of when this is going to happen. (It is now – almost certainly – when not if.)

    Is that because of the uncertainty in timing here, that we can’t accurately predict exactly how soon the ice melt (as noted faster observed than modelled) will really “kick in” even as a rough approximation?

    I think the so-called “pause” in warming that really hasn’t been could end very dramatically and horribly indeed with dreadful consequences for the whole world. Once we do start getting strong El Nino’s* plus completely open Arctic ocean plus a stronger solar activity cycle. Well … (Expletive. Long line of expletives.)

    * Thinking of which, Greg Laden have you and others here seen this piece :

    http://www.slate.com/blogs/future_tense/2014/11/06/el_ni_o_prediction_2014_why_weather_forecasters_were_wrong_about_a_super.html?wpsrc=sh_all_dt_tw_bot

    Whatt’ya think?

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