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A Matter of Millimetres

March 20, 2014

sea level

As a species, we humans are terribly self-centred. Sure, we are interested in the rest of the world, but many of us seem to be interested in it only as far as it affects us. We are stuck in an endless loop of pursuing money so that we can pursue consumer goods, and there is little time left to look at the parts of the world that don’t “matter” (to our wallets).*

World sea level rise is a case in point. There is good evidence that sea level has been rising for the past century or so, and the data on climate change indicate that it will continue to rise in the coming years, perhaps as much as  0.8 to 2.0 metres by the year 2100 (or about 2½ to 6½ feet). The rise is related to global warming, which affects seawater volume by causing glacial ice to melt, and by causing the thermal expansion of the seawater itself.

Morning low tide at Pocologan, New Brunswick

Morning low tide at Pocologan, New Brunswick

Although we are becoming aware of sea level rise, articles I see in the media are mostly about the potential effects on First World coastal cities (notably Venice, New York, New Orleans, and London), or about how it will affect the many people who have moved to low, picturesque coastlines in places like Florida and South Carolina. Occasionally there are pieces that discuss the dramatic and frightening impacts for poor people in the Third World: the heavily populated Ganges Delta in Bangladesh could lose much of its land, with 10% of the country disappearing as a result of a one-metre rise in sea level, and low-lying island countries such as Tuvalu could also be in terrible trouble.

The human effects of sea level change will be seen in different ways in different places; it won’t just appear as a gentle, gradual inexorable rise of the water along the beach, year-in and year-out, slowly working its way up the lawns of pleasant seaside bungalows. Some of the most dire predictions are related to flooding associated with storm surges, but there could also be major issues with increased coastal erosion, with farmland becoming too salty for crops to grow, and with loss of groundwater resources. These impacts on people are serious, potentially fatal in some areas, but what about the non-human world?

Seaweeds on the shore near Black's Harbour, New Brunswick

Seaweeds on the shore near Blacks Harbour, New Brunswick

In many ways, the effects on other organisms will mirror the effects on people. Land-dwelling animals and plants will have to move inland as shorelines advance, and trees will die as the soil becomes too salty to support their growth. Animals will drown in floods caused by storm surges.

In other ways, however, the effects on nature will have few ready analogues in our human world. For instance, increased sea level could modify the salinity of bays and estuaries, affecting the organisms that are able to live there. Considering shorelines, the aspect of sea level rise I think about most often is how it might affect the life of tidal flats and rocky shores.

Water fills shallow depressions in the Pocologan tidal flat.

Water fills shallow depressions in the Pocologan tidal flat.

The Anchorage, Grand Manan Island

A pond on the tidal flat, near The Anchorage, Grand Manan Island

As the name indicates, tidal flats are surfaces with very little relief. Any vertical change of sea level will be amplified by a much greater lateral migration of the sea across a nearly horizontal surface (imagine the movement of spilled water across a tabletop). In addition, many of the life forms on tidal flats are small; a vertical change of a few millimetres would affect them the same way you would be affected by a flood that is metres in depth.

Periwinkle at Pocologan

Periwinkle at Pocologan

Rock crab on Grand Manan

Rock crab on Grand Manan

The life of rocky shores might be less affected by slight vertical changes, but its obvious vertical zonation is a clear demonstration how the organisms are attuned to sea level. Most life forms on tidal shores have their locations finely calibrated with respect to tide cycles: they live where they can best locate food, and where they can also manage to survive the alternations of wetting and drying, the changes in temperature and salinity, and the push and pull of waves. This is why, even from a distance, one can readily see the bands of colour that show the locations of particular algal species.

Algae in a tidal flat channel, St. Andrews, New Brunswick

Algae in a shallow tidal flat channel, St. Andrews, New Brunswick

seaweed bed

Periwinkles on bladderwrack and other seaweeds, Grand Manan Island

The geological record tells us that sea level is always changing; if it wasn’t rising right now, it would be falling. The current rate of change, however, is like nothing in living memory. The shapes of tidal shores have come from the interplay of many factors: organisms, waves and currents, the underlying geology, erosion, and sediment transport, modified through the dimension of time. Non-catastrophic change can occur only so quickly, and it is possible that rapid sea level rise will, for instance, drown some tidal flats without allowing sufficient time for new ones to form. Many tidal flat creatures can move, but only if there is still some tidal flat available to them!

Near North Head, Grand Manan Island

Near North Head, Grand Manan Island

* This self-obsession is entirely obvious when we consider the criteria for scientific research: we are told that research must be relevant, which really means that it must either allow us to make more money or it must directly relate to human society. It really doesn’t matter how relevant the research is to the non-human world, though!

© Graham Young, 2014

4 Comments leave one →
  1. Greg permalink
    March 21, 2014 9:25 am

    There are quite a few people on Grand Manan concerned about sea level rise, although from what I read it is not rising here as rapidly as along coastal areas south of New England. That appears to be due to post-glacial rebound. But sea level rise appears to be accelerating and all of us will be affected.

    • Graham permalink*
      March 21, 2014 9:30 am

      Thanks Greg. I can certainly understand your concern. Is the rise the same on both sides of Grand Manan, and what sort of rise is there? I have seen the old trees that show relative rise at places like Castalia and White Head over the past few thousand years. Rebound is such a huge factor – one other coastal place I work is at Churchill, and there the rebound is great enough that relative sea level should continue to fall.

  2. Gary David Bell permalink
    March 24, 2014 2:15 pm


    I have been reading the posts for a while now, good stuff. Grand Manan is a beautiful place. Yes, we “humans” (Dare I say greedy apes?) are mostly self serving, survival of the fittest gone wild. We are however not very important in the overall picture. Geologically speaking we hardly exist at all, (forget the anthropocene) perhaps another ten million years will give better proof of our capacity to survive in the short term. We do however need to make efforts to clean up our act to get a fair shot at the next few millennia. We often like to see our messes (dramatic) up close, but we represent not much more than a thin patchy film on the surface. There have been larger longer lasting biomasses before us (Trilobites!) and no doubt others are waiting in the wings.

    Best, Gary Bell. Canada

    Date: Thu, 20 Mar 2014 16:20:45 +0000 To:

    • Graham permalink*
      March 24, 2014 3:20 pm

      Thanks for the comment, Gary. You make some very valid points!

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