Posted by: shipbright | November 2, 2009

Climate change and freshwater part 3…rising sea levels and island nations at risk

Recent_Sea_Level_RiseSince the mid to late 1800’s sea levels have been very slowly rising…about 1 cm a year which is so small who would notice?  It’s now been about a century and some change and the rate of rising is starting to accelerate to about 2 cm a year. The tiny changes over the years are becoming noticeable.  Sea levels are rising and we are learning that in the last decade alone the rate is up to about 3cm a year.

venice21The threat of rising sea levels to our coastal cities is being felt around the world such as the  magnificent historical city of Venice, Italy…a place on my “bucket list” [the list of things you want to see and do before you die or “kick the bucket” in American slang].  Poor Venice has a double whammy of both slowly sinking as a result of its own weight on the barrier islands it was constructed upon and a rising Adriatic Sea.  Venice is not alone..more than half of the world’s population lives within 60 Kilometers [36 miles] of the coast and the effects of a rising sea and retreating coastline is a serious issue for all of us.  I’m not going to be focusing on coastal effects here, instead this post is the warm up to the issue of freshwater and island nations.  As you’ve hopefully read in my previous posts I believe that islands hold lessons for the rest of us on the mainlands.  Islands are the “Miner’s Canary” for us and when island nations start running into issues, in this case sea levels and freshwater, we need to pay attention.

You may have seen articles in magazines such as National Geographic on small island nations suffering from sea level rise.   Island nations like Tuvalu, The Maldives, Kiribati, Vanuatu are all feeling the effects of rising sea levels.  It may seem like a marginally interesting or somewhat important issue when something is so far away, it can be hard to feel it and understand its importance to your own world.  But these islands are the harbingers of what’s to come for all of us and we ignore their plight at our own peril.  An organization of these small islands nations called Islands First has an excellent website and is a treasure trove of information on the issues facing these islands:  http://www.islandsfirst.org/

Oceania-map

One of my favorite authors is Sir Laurens van der Post and he writes hauntingly beautiful and insightful novels about his life in South Africa.  In his book, “A Story Like the Wind” he writes about geo-political events that effect his characters on the edges of the remote Kalahari desert.  He says of these events, “they are like the wind, they come from a far off place but we feel them here”.  Here is another story like the wind…Kiribati:

kiribati

…A  small island nation whose government is literally planning for its demise, just like Vanuatu or Tuvalu or the other low-lying atoll island nations of the South Pacific:

There are a couple of factors contributing to sea level rise:  Thermal expansion of the oceans due to warming of the waters, melting glaciers and loss of sea ice.  The Climate Institute has this explanation on this issue and I’ve embedded a NASA video below that presents the information quite nicely:

From the Climate Institute [edited for length] at www.climate.org

Most of the world’s coastal cities were established during the last few millennia, a period when global sea level has been near constant. Since the mid-19th century, sea level has been rising, likely primarily as a result of human-induced climate change. During the 20th century, sea level rose about 15-20 centimeters (roughly 1.5 to 2.0 mm/year), with the rate at the end of the century greater than over the early part of the century. Satellite measurements taken over the past decade, however, indicate that the rate of increase has jumped to about 3.1 mm/year, which is significantly higher than the average rate for the 20th century. Projections suggest that the rate of sea level rise is likely to increase during the 21st century, although there is considerable controversy about the likely size of the increase.

…It should be understood that the melting back of sea ice (e.g., in the Arctic and the floating ice shelves) will not directly contribute to sea level rise because this ice is already floating on the ocean (and so already displacing its mass of water). However, the melting back of this ice can lead to indirect contributions on sea level. For example, the melting back of sea ice leads to a reduction in albedo (surface reflectivity) and allows for greater absorption of solar radiation. More solar radiation being absorbed will accelerate warming, thus increasing the melting back of snow and ice on land. In addition, ongoing break up of the floating ice shelves will allow a faster flow of ice on land into the oceans, thereby providing an additional contribution to sea level rise.

There are three major processes by which human-induced climate change directly affects sea level. First, like air and other fluids, water expands as its temperature increases (i.e., its density goes down as temperature rises). As climate change increases ocean temperatures, initially at the surface and over centuries at depth, the water will expand, contributing to sea level rise due to thermal expansion. Thermal expansion is likely to have contributed to about 2.5 cm of sea level rise during the second half of the 20th century, with the rate of rise due to this term having increased to about 3 times this rate during the early 21st century. Because this contribution to sea level rise depends mainly on the temperature of the ocean, projecting the increase in ocean temperatures provides an estimate of future growth. Over the 21st century, the IPCC’s Fourth Assessment projected that thermal expansion will lead to sea level rise of about 17-28 cm (plus or minus about 50%). That this estimate is less than would occur from a linear extrapolation of the rate during the first decade of the 21st century when all model projections indicate ongoing ocean warming has led to concerns that the IPCC estimate may be too low.

A second, and less certain, contributor to sea level rise is the melting of glaciers and ice caps. IPCC’s Fourth Assessment estimated that, during the second half of the 20th century, melting of mountain glaciers and ice caps led to about a 2.5 cm rise in sea level. This is a higher amount than was caused by the loss of ice from the Greenland and Antarctic ice sheets, which added about 1 cm to the sea level. For the 21st century, IPCC’s Fourth Assessment projected that melting of glaciers and ice caps will contribute roughly 10-12 cm to sea level rise, with an uncertainty of roughly a third. This would represent a melting of roughly a quarter of the total amount of ice tied up in mountain glaciers and small ice caps.

The third process that can cause sea level to rise is the loss of ice mass from Greenland and Antarctica. Were all the ice on Greenland to melt, a process that would likely take many centuries to millennia, sea level would go up by roughly 7 meters. The West Antarctic ice sheet holds about 5 m of sea level equivalent and is particularly vulnerable as much of it is grounded below sea level; the East Antarctic ice sheet, which is less vulnerable, holds about 55 m of sea level equivalent. The models used to estimate potential changes in ice mass are, so far, only capable of estimating the changes in mass due to surface processes leading to evaporation/sublimation and snowfall and conversion to ice. In summarizing the results of model simulations for the 21st century, IPCC reported that the central estimates projected that Greenland would induce about a 2 cm rise in sea level whereas Antarctica would, because of increased snow accumulation, induce about a 2 cm fall in sea level. That there are likely to be problems with these estimates, however, has become clear with recent satellite observations, which indicate that both Greenland and Antarctica are currently losing ice mass, and we are only in the first decade of a century that is projected to become much warmer over its course.

king tide kiribati

While there are obviously many challenges to projecting future sea level rise, even a seemingly small increase in sea level can have a dramatic impact on many coastal environments. Over 600 million people live in coastal areas that are less than 10 meters above sea level, and two-thirds of the world’s cities that have populations over five million are located in these at-risk areas. With sea level projected to rise at an accelerated rate for at least several centuries, very large numbers of people in vulnerable locations are going to be forced to relocate. 

…Unfortunately, many of the nations that are most vulnerable to sea level rise do not have the resources to prepare for it. Low-lying coastal regions in developing countries such as Bangladesh, Vietnam, India, and China have especially large populations living in at-risk coastal areas such as deltas, where river systems enter the ocean. Both large island nations such as the Philippines and Indonesia and small ones such as Tuvalu and Vanuatu are at severe risk because they do not have enough land at higher elevations to support displaced coastal populations. Another possibility for some island nations is the danger of losing their fresh-water supplies as sea level rise pushes saltwater into their aquifers. For these reasons, those living on several small island nations (including the Maldives in the Indian Ocean and the Marshall Islands in the Pacific) could be forced to evacuate over the 21st century.

 20081009_tuvaluposter

Sea level rise can effect the very existence of an island nation, but before it floods over these islands there are other more insidious effects of sea level rise and an island’s freshwater resources are a “Miner’s Canary” of the larger climatic issue.  It presents a clear and present threat to the population long before the waves come over the beach. 

Next post: islands and freshwater

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Responses

  1. WELL THAT WAS NOOOO HELP TO OUR ASSIGNMENT
    love ficken bottom

    • Oh well… What is your assignment? Maybe I can help 🙂


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