A Matter of Millimetres
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.
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?
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.
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.
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.
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!
* 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