Don't ever say I don't bring you fascinating and informative titbits from my wanderings around the climate blogosphere. Here's a gem! Read and inwardly digest, PLEASE! (especially Aubrey).
This is from WUWT http://wattsupwiththat.com/2010/01/27/floating-islands/#more-15762
Floating Islands
27.01.2010
Guest Post by Willis Eschenbach
Much has been written of late regarding the impending projected demise of the world’s coral atoll islands due to CO2-caused sea level rise. Micronesia is suing the Czech Government over CO2 emissions that they claim are damaging their coral atolls via sea level rise. Tuvalu and the Maldives are also repeating their claims of damage from CO2. If the sea level rises much, they say they will simply be swept away.
Recently, here in the Solomon Islands, the sea level rise has been blamed for salt water intrusion into the subsurface “lens” of fresh water that forms under atolls. Beneath the surface of most atolls, there is a lens shaped body of fresh water. The claim is that the rising sea levels are contaminating the fresh-water lens with seawater. On other atolls, increased sea levels are claimed to be washing away parts of the atoll.
In this paper, I will discuss the three inter-related claims that people are making as illustrated above. The claims are:
1. Increasing CO2 causes increased sea level rise.
2. Sea level rise causes salt water to intrude into the freshwater lens
3. Sea level rise gravely endangers low-lying coral atolls like Tuvalu, Kiribati, and the Maldives. A mere 1 metre rise would see them mostly washed away.
I will look at the real causes of the very real problems faced by atoll dwellers. Finally, I will list some practical measures to ameliorate those problems.
And before you ask, how do I know this atoll stuff? For three years I lived on and worked on and had wells dug on and watched the moon rise over and dived in the lagoon and on the reef wall of a coral atoll in the South Pacific … hey, somebody has to … that plus a lot of study and research.
Claim 1. Does increased CO2 cause increased sea level rise?
Short answer, data to date says no. There has been no acceleration the rate of sea level rise. Sea level has been rising for centuries. But the rate of the rise has not changed a whole lot. Both tidal stations and satellites show no increase in the historic rate of sea level rise, in either the short or long term. Fig. 1 shows the most recent satellite data.
![[image]](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_tUEECBdSY2vdhM3SexCJvZPW8E3z8Haxnd-Du0G_reJYP8Ng6q1Ntp1gJK0l7Ih51ixvxhK2zzD6P-Ik2-rePxZvvI1CjnOndyH6csd_FL33V80pmwES5CGAnc4_FfWcIDngasqC5flx2bMHRdDGTcPA=s0-d "[image]")
Figure 1. Change of sea level over time. Radar data from the TOPEX satellite. The light blue line is sea level with monthly anomalies removed. The interval between data points is usually ten days. The gray line is the 1993-2004 linear trend projected to the end of the timeline. Gaussian average using a 71-point filter. Photo taken at Taunovo Bay Resort, Fiji.
Up until about the end of 2004, there was little change in the rate of sea level rise. Since then the rise has slowed down. The average (dark blue line) does not stray far from the trend (black line) up until 1994. Since then, it is well below the projected trend (gray line). We were supposed to be seeing some kind of big acceleration in the sea level rise caused by increased CO2. Instead, we are seeing a decrease in the rate of sea level rise. So the first claim, that increasing CO2 will cause increased rates of sea level rise, is not supported by the evidence.
Note that I am not saying anything about the future. The rate of sea level rise might go up again. What we can say, however, is that there is no hint of acceleration in the record, only deceleration. Claim 1 is false to date.
Claim 2. Can a sea level rise cause salt water to intrude into the freshwater lens?
Short answer, no. To understand what is really happening with the freshwater lens, we’ll start with the geology Here is a cross-section of a typical atoll that I drew up.
![[image]](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_vvDwUTZxg8LZPjF5jg9RM4wnmKiIrEUNJtNQJRKH9G2I53sQKNrBehfciCHZfhXGfJHydHMrgLqSJtBXQP715uZ9_15eoPtzm5did_EUe5fsbofMeoTzggAhOpoysv1J1Kz-NPfuUPOero28NI=s0-d "[image]")
Figure 2. Typical cross section through a coral atoll. The living coral is in the ring between the dotted green line and the beach. The atoll used for the photo in this example is Tepoto Atoll, French Polynesia.
Note that the sea water penetrates throughout the porous coral rubble base. Because fresh water is lighter than salt water, the freshwater lens is floating on this subsurface part of the ocean. The weight of the fresh water pushes down the surface of the sea water underneath it, forming the bottom of the “lens” shape. The lens is wider where the atoll is wider. The amount of fresh water in the lens is a balance between what is added and what is withdrawn or lost. The lens is only replenished by rain.
The important thing here is that the freshwater lens is floating on the sea surface. It’s not like a well on land, with an underground freshwater source with a water-tight layer below it. There is no underground freshwater source on an atoll. It is just a bubble of water, a rain-filled lens is floating on a sea water table in a porous coral rubble and sand substructure. If there is no rain, the fresh water will eventually slowly mix with the salt water and dissipate. When there is rain, you get a floating lens of fresh water, which goes up and down with the underlying sea water.
So the second claim, that a sea level rise can cause the sea water to intrude into the fresh water lens, is not true either. The fresh water lens floats on the sea water below. A rise in the sea level merely moves the lens upwards. It does not cause salt water to intrude into the lens.
3. Would a sea level rise gravely endanger low-lying coral atolls?
Regarding atolls and sea level rise, the most important fact was discovered by none other than Charles Darwin. He realized that coral atolls essentially “float” on the surface of the sea. When the sea rises, the atoll rises with it. They are not solid, like a rock island. They are a pile of sand and rubble. There is always material added and material being lost. Atolls exist in a delicate balance between new sand and coral rubble being added from the reef, and atoll sand and rubble being eroded by wind and wave back into the sea or into the lagoon. As sea level rises, the balance tips in favor of sand and rubble being added to the atoll. The result is that the atoll rises with the sea level.
Darwin’s discovery also explained why coral atolls occur in rings as in Fig. 1 above. They started as a circular inshore coral reef around a volcanic rock island. As the sea level rose, flooding more and more of the island, the coral grew upwards. Eventually the island was drowned by the rising sea levels, and all that is left is the ring of reef and coral atolls.
Why don’t we see atolls getting fifty feet high? Wind erosion keeps atolls from getting too tall. Wind increases rapidly with distance above the ocean. The atolls simply cannot get taller. The sand at that elevation is blown away as fast as it is added. That’s why all atolls are so low-lying.
When the sea level rises, wind erosion decreases. The coral itself continues to grow upwards to match the sea level rise. Because the coral continues to flourish, the flow of sand and rubble onto the atoll continues, and with reduced wind erosion the atoll height increases by the amount of the sea level rise.
Since (as Darwin showed) atolls float up with the sea level, the idea that they will be buried by sea level rises is totally unfounded. Despite never being more than a few metres tall, hey have survived a sea level rise of up to three hundred plus feet (call it a hundred metres) within the last twenty thousand years. Historically they have floated up higher than the peaks of drowned mountains.
So the third claim is not true either. Atolls are created by sea level rise, not destroyed by sea level rise.
What is the real cause of salt water in the lens?
Given that the salt water intrusion can’t be a result of sea level rise (because the lens is floating), why is there salt water in the islanders’ wells? Several factors affect this. First and foremost, the fresh water lens is a limited supply. As island populations increase, more and more water is drawn from the lens. The inevitable end of this is that the water in the wells gets saltier and saltier. This affects both wells and plants, which draw from the same lens. It also leads to unfounded claims that sea level rise is to blame.
The second reason for salt water intrusion into the lens is a reduction in the amount of sand and rubble coming onto the atoll from the reef. When the balance between sand added and sand lost is disturbed, the atoll shrinks. When the atoll shrinks, the lens shrinks.
The third reason is that roads and airstrips and changes in land use and land cover has reduced the amount of rain making it to the lens. Less freshwater in, more saltwater in.
What is the real cause of loss of beach and atoll land?
An atoll is not solid ground. It is is not a constant “thing” in the way a rock island is a thing. An atoll is a not-so-solid eddy in a river of sand and rubble. It is an ever-changing body constantly replenished by a (hopefully) unending stream of building materials. It is a process, not a solid object. On one side, healthy reef plus beaked coral-grazing fish plus storms provide a continuous supply of coral sand and rubble. This sand and rubble are constantly being added to the atoll, making it larger. At the same time, coral sand and rubble are constantly being eaten away by waves and blown away by the wind. The shape of the atoll changes from season to season and from year to year. It builds up on this corner, and the sea washes away that corner.
So if the atoll is shrinking, there’s only a few possibilities. Erosion may have increased. The supply of sand and rubble, the raw atoll construction materials, may have decreased. Currents may have changed from reef damage, dredging, or construction.
Water erosion and current changes are increased by anything that damages or changes the reef. That thin strip of living coral armor is all that stands between a pile of sand and the endless waves. When the reef changes, the atoll changes.
Erosion is also caused by a variety of human activities. Road and path building, house construction, ground cover change, clearing of channels through the reef, the list is long.
The reduction in the supply of coral sand and coral rubble, however, is harder to see. This reduction has two main causes – using of coral for building, and killing the wrong fish. The use of coral as a building material in many atolls is quite common. At times this is done in a way that damages the reef. Anything that affects the health of the reef affects how much atoll building material it produces each year. This is the somewhat visible part of the loss of building materials, the part we can see.
What goes unremarked is the loss of the reef sand, which is essential for the continued existence of the atoll. The major cause for the loss of sand is the indiscriminate, wholesale killing of parrotfish and other beaked reef-grazing fish. A single parrotfish, for example, creates around a hundred kilos of coral sand per year. Parrotfish and other beaked reef fish create the sand by grinding up the coral with their massive jaws, digesting the food, and excreting the ground coral.
Beaked grazing fish are vital for overall coral health, growth, and production. This happens in the same way that pruning makes a tree send up lots of new shoots. The constant grazing by the beaked fish keeps the corals in full production mode. This greatly increases the annual production of coral for sand and rubble.
![[image]](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sXIXgkOQnEWYS50AwVPs8jGWi2vqVgoSNYXtw9XhZXArLnw5CVu7ilIQl5qjxtjOuT95LGWBH566DW2WAJf5eDjHWsIh5GByDe2-874bExJO9VDUmQTva_rC90JauWf314jj4=s0-d "[image]")
Unfortunately, these fish sleep at night, and thus are easily wiped out by night divers. The invention of the diving flashlight has meant that their populations have plummeted in many areas in recent years. Result? Less sand means less beaches, and means more claims of “CO2 is to blame, you can see the damage!”.
Some Practical Suggestions
What can be done to turn the situation around for the atolls? From the outside, not a whole lot. Stopping the Czechs from burning coal won’t do a damned thing. From the outside, we can offer only assistance. The work needs to occur on the atolls themselves.
There are, however, a number of low-cost, practical steps that atoll residents can take to preserve and build up their atolls, and protect the fresh water lens. In no particular order these are:
1. Stop having so many kids. An atoll has a limited supply of water. It cannot support an unlimited population. Enough said.
2. Catch every drop that falls. On the ground, build small dams in any watercourses to encourage the water to soak in to the lens rather than run off to the ocean. Put water tanks under every roof. Dig “recharge wells”, which return filtered surface water to the lens in times of heavy rain. Catch the water off of the runways. On some atolls, they have put gutters on both sides of the airplane runway to catch all of the rainwater falling on the runway. It is collected and pumped into tanks. On other atolls, they let the rainwater just run off of the airstrip back into the ocean …
3. Conserve, conserve, conserve. Use seawater in place of fresh whenever possible. Use as little water as you can.
4. Make the killing of parrotfish and other beaked reef grazing fish tabu. Stop fishing them entirely. Make them protected species. The parrotfish should be the national bird of every atoll nation. I’m serious. If you call it the national bird, tourists will ask why a fish is the national bird, and you can explain to them how the parrotfish is the source of the beautiful beaches they are walking on, so they shouldn’t spear beaked reef fish or eat them. Stop killing the fish that make the very ground underfoot. The parrotfish and the other beaked reef-grazing fish are constantly building up the atoll. Every year they are providing tonnes and tonnes of fine white sand to keep the atoll afloat in turbulent times. They should be honored and protected, not killed. Caring for the reef is the single most important thing you can do.
5. Be cautious regarding the use of coral as a building material. The atoll will be affected if anything upsets that balance of sand added and sand lost. It will erode if the supply of coral sand and rubble per year starts dropping (say from reef damage or extensive coral mining or killing parrotfish) or if the total sand and rubble loss goes up (say by heavy rains or strong winds or human erosion or a change in currents).
So when coral is necessary for building, take it sparingly, in spots. Take dead or dying coral in preference to live coral. Mine the deeps and not the shallows. Use hand tools. Leave enough healthy reef around to reseed the area with new coral. A healthy reef is the factory that annually produces the tonnes and tonnes of building material that is absolutely necessary to keep the atoll afloat. You mess with it at your peril.
6. Reduce sand loss from the atoll in as many ways as possible. This can be done with plants to stop wind erosion. Don’t introduce plants for the purpose. Encourage and transplant the plants that already grow locally. Reducing water erosion also occurs with the small dams mentioned above, which will trap sand eroded by rainfall. Don’t overlook human erosion. Every step a person takes on an atoll pushes sand downhill, closer to returning to the sea. Lay down leaf mats where this is evident, wherever the path is wearing away. People wear a path, and soon it is lower than the surrounding ground. When it rains, it becomes a small watercourse. Invisibly, the water washes the precious sand into the ocean. Invisibly, the wind blows the ground out from underfoot. Protect the island from erosion. Stop it from being washed and blown away.
7. Monitor and build up the health of the reef. You and you alone are responsible for the well-being of the amazing underwater fish-tended coral factory that year after year keeps your atoll from disappearing. Coral reseeding programs done by schools have been very successful. Get the kids involved in watching and recording and photographing the reef. Remind the people that they are the guardians of the reef. Talk to the fishermen.
8. Expand the atoll. Modern coastal engineering has shown that it is often quite possible to “grow” an atoll. The key is to slow down the water as it passes by. The slower the water moves, the more sand drops out to the bottom. Slowing the water is accomplished by building low underwater walls perpendicular to the coastline. These start abovewater, and run out until the ends are a few metres underwater. Commercially this is done with a geotextile fabric tubes which are pumped full of concrete. See the references for more information. In the atolls the similar effect can be obtained with “gabbions”, wire cages filled with blocks of dead coral. Wire all of the wire cages securely together in a triangular pattern, stake them down with rebar, wait for the sand to fill in. It might be possible to do it with old tires, fastened together, with chunks of coral piled on top of them. It will likely take a few years to fill in. This triangular shape does not attempt to stop the water currents. Think of it as a speed bunp. It just slows the currents down and directs them toward the beach to deposit their load of sand. Eventually, the entire area fills in with sand.
Of course to do that, you absolutely have to have a constant source of sand and rubble … like for example a healthy reef with lots of parrotfish. That’s why I said above that the most important thing is to protect the fish and the reef. If you have a healthy reef, you’ll have plenty of sand and rubble to keep the atoll afloat forever. If you don’t, you’re in trouble.
Coral atolls have proven over thousands of years that, if left alone, they can go up with the sea level. And if we follow some simple conservation practices, they can continue to do so and to support atoll residents. But they cannot survive an unlimited population increase, or unrestricted overfishing, or overpumping the water lens, or unrestrained coral mining. Those are what is killing the atolls, not the same sea level rise that we’ve had for the last hundred years.
FURTHER REFERENCES:
On global sea level rise levelling off: University of Colorado at Boulder Sea Level Change, http://sealevel.colorado.edu
On Darwin’s discovery: Darwin, C., The Autobiography of Charles Darwin 1809-1882, 1887
“No other work of mine was begun in so deductive a spirit as this; for the whole theory was thought out on the west coast of S. America before I had seen a true coral reef. I had therefore only to verify and extend my views by a careful examination of living reefs. But it should be observed that I had during the two previous years been incessantly attending to the effects on the shores of S. America of the intermittent elevation of the land, together with the denudation and deposition of sediment. This necessarily led me to reflect much on the effects of subsidence, and it was easy to replace in imagination the continued deposition of sediment by the upward growth of coral. To do this was to form my theory of the formation of barrier-reefs and atolls.” (Darwin, 1887, p. 98, 99)
On the results of coral mining and changing the reef: Xue, C. (1996) Coastal Erosion And Management Of Amatuku Island, Funafuti Atoll, Tuvalu, 1996, South Pacific Applied Geoscience Commission (SOPAC),http://conf.sopac.org/virlib/TR/TR0234.pdf This atoll was cited by the Sierra Club as an example of the dangers of sea level rise. The truth is more prosaic.
On the same topic: Xue, C., Malologa, F. (1995) Coastal sedimentation and coastal management of Fongafale, Funafuti, Tuvalu, SOPAC Technical Report 221
More information on how parrotfish increase reef production: http://www.esajournals.org/doi/abs/10.1890/1051-0761(2006)016%5B0747:TIOEGS%5D2.0.CO%3B2
On the cause of erosion in Tuvalu: Tuvalu Not Experiencing Increased Sea Level Rise, Willis Eschenbach, Energy & Environment, Volume 15, Number 3, 1 July 2004 , pp. 527-543,http://homepage.mac.com/williseschenbach/.Public/Sinking_In_Tuvalu.doc
This is from WUWT http://wattsupwiththat.com/2010/01/27/floating-islands/#more-15762
Floating Islands
27.01.2010
Guest Post by Willis Eschenbach
Much has been written of late regarding the impending projected demise of the world’s coral atoll islands due to CO2-caused sea level rise. Micronesia is suing the Czech Government over CO2 emissions that they claim are damaging their coral atolls via sea level rise. Tuvalu and the Maldives are also repeating their claims of damage from CO2. If the sea level rises much, they say they will simply be swept away.
Recently, here in the Solomon Islands, the sea level rise has been blamed for salt water intrusion into the subsurface “lens” of fresh water that forms under atolls. Beneath the surface of most atolls, there is a lens shaped body of fresh water. The claim is that the rising sea levels are contaminating the fresh-water lens with seawater. On other atolls, increased sea levels are claimed to be washing away parts of the atoll.
In this paper, I will discuss the three inter-related claims that people are making as illustrated above. The claims are:
1. Increasing CO2 causes increased sea level rise.
2. Sea level rise causes salt water to intrude into the freshwater lens
3. Sea level rise gravely endangers low-lying coral atolls like Tuvalu, Kiribati, and the Maldives. A mere 1 metre rise would see them mostly washed away.
I will look at the real causes of the very real problems faced by atoll dwellers. Finally, I will list some practical measures to ameliorate those problems.
And before you ask, how do I know this atoll stuff? For three years I lived on and worked on and had wells dug on and watched the moon rise over and dived in the lagoon and on the reef wall of a coral atoll in the South Pacific … hey, somebody has to … that plus a lot of study and research.
Claim 1. Does increased CO2 cause increased sea level rise?
Short answer, data to date says no. There has been no acceleration the rate of sea level rise. Sea level has been rising for centuries. But the rate of the rise has not changed a whole lot. Both tidal stations and satellites show no increase in the historic rate of sea level rise, in either the short or long term. Fig. 1 shows the most recent satellite data.
Figure 1. Change of sea level over time. Radar data from the TOPEX satellite. The light blue line is sea level with monthly anomalies removed. The interval between data points is usually ten days. The gray line is the 1993-2004 linear trend projected to the end of the timeline. Gaussian average using a 71-point filter. Photo taken at Taunovo Bay Resort, Fiji.
Up until about the end of 2004, there was little change in the rate of sea level rise. Since then the rise has slowed down. The average (dark blue line) does not stray far from the trend (black line) up until 1994. Since then, it is well below the projected trend (gray line). We were supposed to be seeing some kind of big acceleration in the sea level rise caused by increased CO2. Instead, we are seeing a decrease in the rate of sea level rise. So the first claim, that increasing CO2 will cause increased rates of sea level rise, is not supported by the evidence.
Note that I am not saying anything about the future. The rate of sea level rise might go up again. What we can say, however, is that there is no hint of acceleration in the record, only deceleration. Claim 1 is false to date.
Claim 2. Can a sea level rise cause salt water to intrude into the freshwater lens?
Short answer, no. To understand what is really happening with the freshwater lens, we’ll start with the geology Here is a cross-section of a typical atoll that I drew up.
Figure 2. Typical cross section through a coral atoll. The living coral is in the ring between the dotted green line and the beach. The atoll used for the photo in this example is Tepoto Atoll, French Polynesia.
Note that the sea water penetrates throughout the porous coral rubble base. Because fresh water is lighter than salt water, the freshwater lens is floating on this subsurface part of the ocean. The weight of the fresh water pushes down the surface of the sea water underneath it, forming the bottom of the “lens” shape. The lens is wider where the atoll is wider. The amount of fresh water in the lens is a balance between what is added and what is withdrawn or lost. The lens is only replenished by rain.
The important thing here is that the freshwater lens is floating on the sea surface. It’s not like a well on land, with an underground freshwater source with a water-tight layer below it. There is no underground freshwater source on an atoll. It is just a bubble of water, a rain-filled lens is floating on a sea water table in a porous coral rubble and sand substructure. If there is no rain, the fresh water will eventually slowly mix with the salt water and dissipate. When there is rain, you get a floating lens of fresh water, which goes up and down with the underlying sea water.
So the second claim, that a sea level rise can cause the sea water to intrude into the fresh water lens, is not true either. The fresh water lens floats on the sea water below. A rise in the sea level merely moves the lens upwards. It does not cause salt water to intrude into the lens.
3. Would a sea level rise gravely endanger low-lying coral atolls?
Regarding atolls and sea level rise, the most important fact was discovered by none other than Charles Darwin. He realized that coral atolls essentially “float” on the surface of the sea. When the sea rises, the atoll rises with it. They are not solid, like a rock island. They are a pile of sand and rubble. There is always material added and material being lost. Atolls exist in a delicate balance between new sand and coral rubble being added from the reef, and atoll sand and rubble being eroded by wind and wave back into the sea or into the lagoon. As sea level rises, the balance tips in favor of sand and rubble being added to the atoll. The result is that the atoll rises with the sea level.
Darwin’s discovery also explained why coral atolls occur in rings as in Fig. 1 above. They started as a circular inshore coral reef around a volcanic rock island. As the sea level rose, flooding more and more of the island, the coral grew upwards. Eventually the island was drowned by the rising sea levels, and all that is left is the ring of reef and coral atolls.
Why don’t we see atolls getting fifty feet high? Wind erosion keeps atolls from getting too tall. Wind increases rapidly with distance above the ocean. The atolls simply cannot get taller. The sand at that elevation is blown away as fast as it is added. That’s why all atolls are so low-lying.
When the sea level rises, wind erosion decreases. The coral itself continues to grow upwards to match the sea level rise. Because the coral continues to flourish, the flow of sand and rubble onto the atoll continues, and with reduced wind erosion the atoll height increases by the amount of the sea level rise.
Since (as Darwin showed) atolls float up with the sea level, the idea that they will be buried by sea level rises is totally unfounded. Despite never being more than a few metres tall, hey have survived a sea level rise of up to three hundred plus feet (call it a hundred metres) within the last twenty thousand years. Historically they have floated up higher than the peaks of drowned mountains.
So the third claim is not true either. Atolls are created by sea level rise, not destroyed by sea level rise.
What is the real cause of salt water in the lens?
Given that the salt water intrusion can’t be a result of sea level rise (because the lens is floating), why is there salt water in the islanders’ wells? Several factors affect this. First and foremost, the fresh water lens is a limited supply. As island populations increase, more and more water is drawn from the lens. The inevitable end of this is that the water in the wells gets saltier and saltier. This affects both wells and plants, which draw from the same lens. It also leads to unfounded claims that sea level rise is to blame.
The second reason for salt water intrusion into the lens is a reduction in the amount of sand and rubble coming onto the atoll from the reef. When the balance between sand added and sand lost is disturbed, the atoll shrinks. When the atoll shrinks, the lens shrinks.
The third reason is that roads and airstrips and changes in land use and land cover has reduced the amount of rain making it to the lens. Less freshwater in, more saltwater in.
What is the real cause of loss of beach and atoll land?
An atoll is not solid ground. It is is not a constant “thing” in the way a rock island is a thing. An atoll is a not-so-solid eddy in a river of sand and rubble. It is an ever-changing body constantly replenished by a (hopefully) unending stream of building materials. It is a process, not a solid object. On one side, healthy reef plus beaked coral-grazing fish plus storms provide a continuous supply of coral sand and rubble. This sand and rubble are constantly being added to the atoll, making it larger. At the same time, coral sand and rubble are constantly being eaten away by waves and blown away by the wind. The shape of the atoll changes from season to season and from year to year. It builds up on this corner, and the sea washes away that corner.
So if the atoll is shrinking, there’s only a few possibilities. Erosion may have increased. The supply of sand and rubble, the raw atoll construction materials, may have decreased. Currents may have changed from reef damage, dredging, or construction.
Water erosion and current changes are increased by anything that damages or changes the reef. That thin strip of living coral armor is all that stands between a pile of sand and the endless waves. When the reef changes, the atoll changes.
Erosion is also caused by a variety of human activities. Road and path building, house construction, ground cover change, clearing of channels through the reef, the list is long.
The reduction in the supply of coral sand and coral rubble, however, is harder to see. This reduction has two main causes – using of coral for building, and killing the wrong fish. The use of coral as a building material in many atolls is quite common. At times this is done in a way that damages the reef. Anything that affects the health of the reef affects how much atoll building material it produces each year. This is the somewhat visible part of the loss of building materials, the part we can see.
What goes unremarked is the loss of the reef sand, which is essential for the continued existence of the atoll. The major cause for the loss of sand is the indiscriminate, wholesale killing of parrotfish and other beaked reef-grazing fish. A single parrotfish, for example, creates around a hundred kilos of coral sand per year. Parrotfish and other beaked reef fish create the sand by grinding up the coral with their massive jaws, digesting the food, and excreting the ground coral.
Beaked grazing fish are vital for overall coral health, growth, and production. This happens in the same way that pruning makes a tree send up lots of new shoots. The constant grazing by the beaked fish keeps the corals in full production mode. This greatly increases the annual production of coral for sand and rubble.
Unfortunately, these fish sleep at night, and thus are easily wiped out by night divers. The invention of the diving flashlight has meant that their populations have plummeted in many areas in recent years. Result? Less sand means less beaches, and means more claims of “CO2 is to blame, you can see the damage!”.
Some Practical Suggestions
What can be done to turn the situation around for the atolls? From the outside, not a whole lot. Stopping the Czechs from burning coal won’t do a damned thing. From the outside, we can offer only assistance. The work needs to occur on the atolls themselves.
There are, however, a number of low-cost, practical steps that atoll residents can take to preserve and build up their atolls, and protect the fresh water lens. In no particular order these are:
1. Stop having so many kids. An atoll has a limited supply of water. It cannot support an unlimited population. Enough said.
2. Catch every drop that falls. On the ground, build small dams in any watercourses to encourage the water to soak in to the lens rather than run off to the ocean. Put water tanks under every roof. Dig “recharge wells”, which return filtered surface water to the lens in times of heavy rain. Catch the water off of the runways. On some atolls, they have put gutters on both sides of the airplane runway to catch all of the rainwater falling on the runway. It is collected and pumped into tanks. On other atolls, they let the rainwater just run off of the airstrip back into the ocean …
3. Conserve, conserve, conserve. Use seawater in place of fresh whenever possible. Use as little water as you can.
4. Make the killing of parrotfish and other beaked reef grazing fish tabu. Stop fishing them entirely. Make them protected species. The parrotfish should be the national bird of every atoll nation. I’m serious. If you call it the national bird, tourists will ask why a fish is the national bird, and you can explain to them how the parrotfish is the source of the beautiful beaches they are walking on, so they shouldn’t spear beaked reef fish or eat them. Stop killing the fish that make the very ground underfoot. The parrotfish and the other beaked reef-grazing fish are constantly building up the atoll. Every year they are providing tonnes and tonnes of fine white sand to keep the atoll afloat in turbulent times. They should be honored and protected, not killed. Caring for the reef is the single most important thing you can do.
5. Be cautious regarding the use of coral as a building material. The atoll will be affected if anything upsets that balance of sand added and sand lost. It will erode if the supply of coral sand and rubble per year starts dropping (say from reef damage or extensive coral mining or killing parrotfish) or if the total sand and rubble loss goes up (say by heavy rains or strong winds or human erosion or a change in currents).
So when coral is necessary for building, take it sparingly, in spots. Take dead or dying coral in preference to live coral. Mine the deeps and not the shallows. Use hand tools. Leave enough healthy reef around to reseed the area with new coral. A healthy reef is the factory that annually produces the tonnes and tonnes of building material that is absolutely necessary to keep the atoll afloat. You mess with it at your peril.
6. Reduce sand loss from the atoll in as many ways as possible. This can be done with plants to stop wind erosion. Don’t introduce plants for the purpose. Encourage and transplant the plants that already grow locally. Reducing water erosion also occurs with the small dams mentioned above, which will trap sand eroded by rainfall. Don’t overlook human erosion. Every step a person takes on an atoll pushes sand downhill, closer to returning to the sea. Lay down leaf mats where this is evident, wherever the path is wearing away. People wear a path, and soon it is lower than the surrounding ground. When it rains, it becomes a small watercourse. Invisibly, the water washes the precious sand into the ocean. Invisibly, the wind blows the ground out from underfoot. Protect the island from erosion. Stop it from being washed and blown away.
7. Monitor and build up the health of the reef. You and you alone are responsible for the well-being of the amazing underwater fish-tended coral factory that year after year keeps your atoll from disappearing. Coral reseeding programs done by schools have been very successful. Get the kids involved in watching and recording and photographing the reef. Remind the people that they are the guardians of the reef. Talk to the fishermen.
8. Expand the atoll. Modern coastal engineering has shown that it is often quite possible to “grow” an atoll. The key is to slow down the water as it passes by. The slower the water moves, the more sand drops out to the bottom. Slowing the water is accomplished by building low underwater walls perpendicular to the coastline. These start abovewater, and run out until the ends are a few metres underwater. Commercially this is done with a geotextile fabric tubes which are pumped full of concrete. See the references for more information. In the atolls the similar effect can be obtained with “gabbions”, wire cages filled with blocks of dead coral. Wire all of the wire cages securely together in a triangular pattern, stake them down with rebar, wait for the sand to fill in. It might be possible to do it with old tires, fastened together, with chunks of coral piled on top of them. It will likely take a few years to fill in. This triangular shape does not attempt to stop the water currents. Think of it as a speed bunp. It just slows the currents down and directs them toward the beach to deposit their load of sand. Eventually, the entire area fills in with sand.
Of course to do that, you absolutely have to have a constant source of sand and rubble … like for example a healthy reef with lots of parrotfish. That’s why I said above that the most important thing is to protect the fish and the reef. If you have a healthy reef, you’ll have plenty of sand and rubble to keep the atoll afloat forever. If you don’t, you’re in trouble.
Coral atolls have proven over thousands of years that, if left alone, they can go up with the sea level. And if we follow some simple conservation practices, they can continue to do so and to support atoll residents. But they cannot survive an unlimited population increase, or unrestricted overfishing, or overpumping the water lens, or unrestrained coral mining. Those are what is killing the atolls, not the same sea level rise that we’ve had for the last hundred years.
FURTHER REFERENCES:
On global sea level rise levelling off: University of Colorado at Boulder Sea Level Change, http://sealevel.colorado.edu
On Darwin’s discovery: Darwin, C., The Autobiography of Charles Darwin 1809-1882, 1887
“No other work of mine was begun in so deductive a spirit as this; for the whole theory was thought out on the west coast of S. America before I had seen a true coral reef. I had therefore only to verify and extend my views by a careful examination of living reefs. But it should be observed that I had during the two previous years been incessantly attending to the effects on the shores of S. America of the intermittent elevation of the land, together with the denudation and deposition of sediment. This necessarily led me to reflect much on the effects of subsidence, and it was easy to replace in imagination the continued deposition of sediment by the upward growth of coral. To do this was to form my theory of the formation of barrier-reefs and atolls.” (Darwin, 1887, p. 98, 99)
On the results of coral mining and changing the reef: Xue, C. (1996) Coastal Erosion And Management Of Amatuku Island, Funafuti Atoll, Tuvalu, 1996, South Pacific Applied Geoscience Commission (SOPAC),http://conf.sopac.org/virlib/TR/TR0234.pdf This atoll was cited by the Sierra Club as an example of the dangers of sea level rise. The truth is more prosaic.
On the same topic: Xue, C., Malologa, F. (1995) Coastal sedimentation and coastal management of Fongafale, Funafuti, Tuvalu, SOPAC Technical Report 221
More information on how parrotfish increase reef production: http://www.esajournals.org/doi/abs/10.1890/1051-0761(2006)016%5B0747:TIOEGS%5D2.0.CO%3B2
On the cause of erosion in Tuvalu: Tuvalu Not Experiencing Increased Sea Level Rise, Willis Eschenbach, Energy & Environment, Volume 15, Number 3, 1 July 2004 , pp. 527-543,http://homepage.mac.com/williseschenbach/.Public/Sinking_In_Tuvalu.doc
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QUESTION:"If this post is accurate, how can it be that the leaders of these atolls can make claims that they’re sinking due to sea level rises and be taken seriously on the international stage (regardless of the cause of those sea level rises)?
Is the culture of fear so great that one is cautious of even correcting the most obvious of mistakes? Or is ignorance/laziness the dominating factor?"
REPLY: Follow the money!
Is the culture of fear so great that one is cautious of even correcting the most obvious of mistakes? Or is ignorance/laziness the dominating factor?"
REPLY: Follow the money!
Kasmir said Good post Willis, but to expand on what you wrote, the central reason that atolls don’t drown stems from the growth rate of the reef-building corals. “Modern” stony corals, particularly the ubiquitous Acropora genus, grow at about 6″ per year in tropical conditions. That’s about 50X the average sea level rise we’ve been seeing, so the reef tops easily keep up with the sea level rise. Wave action especially during storms does indeed regularly throw coral rubble (and sometimes live reef) atop the living reef above sea level, where it rapidly erodes as you describe, sustaining the intermittent ring of low-lying sandy islands that make up an atoll. So it would take an incredibly enormous increase in sea level rise to “drown” live coral reefs. It’s also worth observing that all corals are colonial animals and also sexually reproduce via sporulation. and the spores can travel long distances to establish new colonies. Hence coral have been able to cope with many, many dramatic and even abrupt climate changes in earth’s history. Particular configurations of coral colonies are always growing and renewing themselves, and are fundamentally transient. the Great Barrier Reef is about the same age as the Great Pyramids. As a class, coral has been around for 500m+ years and has survived numerous extinction events. Coral is quite resilient. The principle impact of any further global warming would be to extend its range to higher latitudes. ...... Luboš Motl said: Even according to top IPCC predictions for sea level rise, all of Pruné power plant will increase the sea levels by 42 microns in 25 years. http://motls.blogspot.com/2009/12/micronesia-will-be-sunk-by-czech-coal.html The Micronesian environment minister has revealed in the interview for Czech counterpart of the Wall Street Journal that the whole protest was inspired by Greenpeace who are also sending them all the data and technical details (probably including the format and legal issues): http://motls.blogspot.com/2010/01/micronesian-minister-greenpeace-tells.html Greenpeace means Greenpeace CZ, and its boss for energy and climate campaigns, Mr Jan Rovenský, who was my friend for 2 weeks back in 1988 when we were teaching Czech to the Russians in our (Pilsen’s) twin city, Yekaterinburg (then Sverdlovsk). Rovenský sent a similar proposal to sue the Czech Republic to all island countries in the world – but he said that he was still shocked that one of them, Micronesia, actually said Yes. Alexander said: Growing up with Maori and Polynesian people, I know they are as keen to make a buck as anyone and no doubt Melanesians are similar. I get angry about the sheer dishonesty of Greenpeace and other advocacy groups who encourage very expensive (for the Islanders) and totally cycnical court actions which, hopefully, have no chance of success. The Tuvaluans dynamited their reef for easier access, which has wrecked the natural balance and structure of their very fragile island. The Carteret Islands in Papua are actually perched on the peak of an undersea volcano, which is shrinking rapidly as it cools. The sea there is not rising, the Islands, only 1.5 or so metres above the high tide line, are sinking with the volcano. Andrey Levin says: Increased freshwater usage is not the problem. The problem is discharge of untreated sewage straight into the ocean. Properly treated sewage (which was fresh water moments before it was used in shower, sink, or toilet) could be 100% reintroduced back into “recharge wells”. It is done, for example, in Israel, and on massive scale. brc says: When you think about it though, a Coral Atoll is almost the only piece of land that doesn’t have a problem with sea levels, given the coral will always grow right up to the bottom of the low tide level. Thanks for pointing this out. | ||
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