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 saltwater intrusion into the subsurface “lens” of freshwater 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 freshwater 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 two interrelated claims that people are making as illustrated above. The claims are:
1. Sea level rise causes salt water to intrude into the freshwater lens
2. Sea level rise gravely endangers low-lying coral atolls like Tuvalu, Kiribati, and the Maldives. A mere 1-meter 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. 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 1. 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. Click image to embiggen.
Note that the seawater 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 freshwater pushes down the surface of the seawater underneath it, forming the bottom of the “lens” shape. The lens is wider in areas 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 floating on a seawater table in a porous coral rubble and sand substructure. If there is no rain, the freshwater 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 seawater.
So the second claim, that a sea level rise can cause the sea water to intrude into the freshwater lens, is not true either. The freshwater lens floats on the seawater below. A rise in the sea level merely moves the lens upwards. It does not cause salt water to intrude into the lens.
Claim 2. 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. 2 above. They started as a circular inshore coral reef around a volcanic rock island. As the sea level rose (or equally, if the island sank), 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 meters tall, they have survived a sea level rise of up to three hundred plus feet (call it a hundred meters) 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 saltwater intrusion can’t be a result of sea level rise (because the lens is floating), why is there saltwater in the islanders’ wells? Several factors affect this. First and foremost, the freshwater 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 saltwater 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 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 reefs 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 are 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 and bony throats, 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 freshwater 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 into 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 rate of 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, available here (PDF doc).
On expanding island beaches: Holmberg Technologies, http://www.erosion.com/
On the atolls getting larger: Global-scale changes in the area of atoll islands during the 21st century
On the dangers of overpopulation: Just look around you …
——————————————————-
[UPDATE June 3, 2010] Other scientists are catching up with me (emphasis mine).
Global and Planetary Change, Article in Press, Accepted Manuscript, doi:10.1016/j.gloplacha.2010.05.003
The dynamic response of reef islands to sea level rise: evidence from multi-decadal analysis of island change in the central pacific
Arthur P. Webb a, and Paul S. Kench b; a South Pacific Applied Geoscience Commission, SOPAC. Fiji; b School of Environment, The University of Auckland, Private Bag 92019, Auckland, New Zealand
Received 22 February 2010; accepted 13 May 2010. Available online 21 May 2010.
Abstract
Low-lying atoll islands are widely perceived to erode in response to measured and future sea level rise. Using historical aerial photography and satellite images this study presents the first quantitative analysis of physical changes in 27 atoll islands in the central Pacific over a 19 to 61 year period. This period of analysis corresponds with instrumental records that show a rate of sea level rise of 2.0 mm.y-1 in the Pacific.
Results show that 86% of islands remained stable (43%) or increased in area (43%) over the timeframe of analysis. Largest decadal rates of increase in island area range between 0.1 to 5.6 hectares. Only 14% of study islands exhibited a net reduction in island area.
Despite small net changes in area, islands exhibited larger gross changes. This was expressed as changes in the planform configuration and position of islands on reef platforms. Modes of island change included: ocean shoreline displacement toward the lagoon; lagoon shoreline progradation; and, extension of the ends of elongate islands. Collectively these adjustments represent net lagoonward migration of islands in 65% of cases.
Results contradict existing paradigms of island response and have significant implications for the consideration of island stability under ongoing sea level rise in the central Pacific.
First, islands are geomorphologically persistent features on atoll reef platforms and can increase in island area despite sea level change.
Second; islands are dynamic landforms that undergo a range of physical adjustments in responses to changing boundary conditions, of which sea level is just one factor.
Third, erosion of island shorelines must be reconsidered in the context of physical adjustments of the entire island shoreline as erosion may be balanced by progradation on other sectors of shorelines. Results indicate that the style and magnitude of geomorphic change will vary between islands. Therefore, Island nations must place a high priority on resolving the precise styles and rates of change that will occur over the next century and reconsider the implications for adaption.
In other words, the islands are floating upwards with the sea level rise, just as I had said. So for those in the comments section who think I’m just making this up … think again. In particular, the final comment by lkrndu22 says that I am “hoist by my own petard” because ocean acidification has already caused “evident and severe” damage … ‘fraid not. The islands continue to rise. The main cause of damage to the corals is … coral mining and killing the fish. And islands where that is happening are in danger, as I indicated above.
But sea level rise? The atolls have lived through that for thousands of years without damage.
JER0ME (00:51:23) :
“The same is true of any finite resource. At 7% increase in consumption (and I think China will make that a joke), we use the same amount every decade as has EVER been used before. Once we hit 50% of all the fossil fuels, we have 10 more years and then no more at all. None. That is just at a mere 7% increase a year.
This seriously call for a really hard look at some kind of resource that is not finite. What’s that word again? Oh yes, “renewable”.
Now that is an argument I can take on board. Sod CO2!
Well Jerome, you may be ace at mathematics, but economics is obviously not your strong suit.
History shows the ‘peak’ anything never pans out that way, as the base assumptions never come true. As oil supply reduces, the cost of oil increases and will eventually reach the point were other forms of energy are cheaper, so consumption then starts to decline. There are many ways to produce energy which are not used because of the high cost and many more will be discovered in the future.
The intelligent ape Homo sapiens is a very creative animal and the bigger the population the more the chance for creative geniuses to be born. Could be an interesting problem for a maths expert to work out how many more?
Wonderful science lesson. How many quarter units do I receive? Made me think of that bottle of water from Fiji my sister left on my table. What will pumping and selling their aquifers do to the atolls? I doubt we will see this research discussed on fijigreen.com.
On the various reported sea level rates of increase
My apologies if I’m repeating something already posted in comments. Someone above pointed to the Leuliette 2004 paper. it should be noted that Leliette adds in some 0.3 mm per year increase to adjust for crustal movement. That is, they are not reporting what the observed seal level rise is. They are reporting what assume the sea level rise would be in the absence of the deflection of oceanic crust. it’s not real. It’s an estimate of what sea level rise would be on an earth that is in complete stasis with respect to crustal movement.
Very interesting, I enjoyed reading that a lot:)
Andrew Parker
Yes, getting the power from the off shore device and THEN into the national grid is a huge unresolved problem. It means x miles of underwater cable at huge cost then linking it to transmission lines at some convenient coastal location-the only problem is that there are very few places where those transmission lines exist on the coast.
The on shore wind industry is starting to recognise that reality, and there are huge and intrusive plans to build transmission lines from often remote and lovely spots where the wind farms are situated, to where it will be needed.
I suspect there is salami slicing going on with these (very) negative aspects only being admitted to bit by bit.
Check out ‘wave hub’ in Cornwall where experimental wave devices will plug into a giant underwater socket then link in to a convenient sub station at nearby Hayle. The number of places where that sort of unobtrusive scenario can be played out is very limited indeed (in the UK).
Tonyb
The head post characterizes the sea level rise as “leveling off”. I think that is overstating the case.
Like many things in the climate, the accuracy of this statement depends upon the timeframe. Yes, the rate-of-rsie has slowed a bit since 2004. But the whole satellite record runs about 3.2mm/yr, while the historical tide gauge record going back to 1870 is around 1.7mm/yr.
On the other hand, a closer look at the historical tide gauge records shows significant variation over spans of several decades. The tide gauge record for the 65 year period 1870-1935 the rate of rise is a bit only about 1.1 mm/yr. Then from 1935 to 1960 the rate increase to about 3 mm/yr. So it appears that there have been significant changes in the rate of sea level rise over spans of several decades. Of course, just like the global average temperature has been generally rising since the end of the last ice age, sea levels have also been generally rising.
I is unwise for either sceptics or AGW alarmists to unduly focus on the changes of just a few years, or even changes over just a few decades.
The chart at http://www.cmar.csiro.au/sealevel/index.html IMO give a good perspective of both the historical tide gauge record and the much shorter satellite record.
Replies to various commenters. I’ve been involved in mariculture of coral for almost 20 years, so I know a bit about the subject.
“One thing I have noticed is that damage to coral reefs in this area gets worse the closer you are to mainland Australia. The close in reefs are in fairly poor condition. The dive sites a little further out really arent in bad condition and the reefs like Osprey which are up to 200km off the mainland I would describe as pretty much pristine and I have plenty of video footage to back this up.
I’m not a scientist but this raises some questions for me and makes me think that most of the reef damage closer in is probably related to agricultural run off and to some extent tourism (large amounts of inexperienced divers and boat traffic can play havoc with a reef).”
Absolutely correct, agricultural runoff is dangerous to inshore reef corals. The principal mechanism is overfertilization which causes macro algae to overgrow to the coral and kill it.
“So 14.5-22 meters (45-70 feet) of coral has accumulated in about 10,000 years, and the reef (if left in peace) is capable of keeping up with a sea-level rise of more than 15 mm/yr, i. e. five times the current rate, or equivalent to at least 1.35 meters (4.5 feet) to 2100.”
The Eniwetok reef has deposited over a kilometer of limestone on top of the now submerged seamount. The principal reef building stony corals such as Acropora, Montipora, and Porites can grow at 150 mm/yr. Reefs are in no danger of drowning from sea level rise. On the contrary, you might think of a coral reef as almost pressing against the surface layer as it attempts to grow towards the sun.
“Not quite true in the long run. Sooner or later the corals always lose out to sea-level rise. There are no really old atolls, geologically speaking. As the volcanic islands move away from the spreading ridges and hotspots where they are created yhe seabottom they stand on gradually subsides and the “high” islands become “low” and ultimately change to atolls which for a while keep up with subsidence but finally become submarine reefs and ultimately seamounts (a. k. a. guyots). The whole process takes several million years, and is beautifully illustrated by the Hawaii island chain, from Big Island (active volcanoes) through the “high” islands getting ever lower to the west and turning into atolls, and ultimately to seamounts west of Midway. Also there is a new island building SE of Big Island (Loihi seamount) which is now less than 1000 meters below sea level and will very likely “surface” within a few thousand years.”
Keep in mind that even at current temperatures, the Hawaiian chain is the far northern range limit of reef building coral. Kure/Midway are the highest latitude coral reefs in the world. The limited coral diversity of the Hawaiian reefs reflects this. The Hawaiian seamount chain extends to the northwest, i.e. to still higher latitudes. It’s not surprising that atolls failed in those latitudes to form or keep up with the sea level rises coming out of the glacial periods when temperatures were still colder in those latitudes.
If we do assume that the global sea level is rising, and perhaps accelerating in rate-of-rise, does it matter?
Some wise climatologists have pointed out that normal year-to-year variation of climate in any given location is much larger than any overall trend due to global warming. So global warming is indetectable in the climate record an any given location. Only when looking at averages over many, many locations does the global warming become detectable.
Sea level rise appears to be similar in that contrary to what might seem to be common sense, the global sea level varies significantly from place to place, due to things such as varying barometric pressure and changes in ocean currents. In addition, the local land level at any given spot is subject to signfiicant change. All of these changes tend to hide the effect of any global average sea level change.
Willis has pointed out how atolls automatically respond to changing sea levels. Human civilization has also gradually changed and adapted to changing sea levels. We survived the changes in sea level over the last couple hundred years with essentially nobody noticing. In the few places where it is a big issue, such as Venice, the problem is usually land subsidence, not changes in the sea level itself.
I always wondered how sea level could rise in one place in the ocean, and a few hundred miles over, not rise at all.
You have to laugh at all the papers written about how sea level rise has affected New Orleans – which is sitting on the edge of a plate and the land is sinking!
Charlie A
AS I posted earlier the sea level history is nonsensical and is based on interpolation and extrapolation of a very tiny number of unrepresentative tidal gauges. Chapter 5 in AR4 -particularly the charts-describe what manipluation has been going on.
tonyb
latitude (12:37:58) :
“You have to laugh at all the papers written about how sea level rise has effected New Orleans – which is sitting on the edge of a plate and the land is sinking”
The flooding of deltas needs a paper like Willis’s – there has been so much dreck about the sinking Ganges Delta- particulary from BBC reports. It’s apparently not as widely known as it should be that delta’s, too, rise with rise in sea level. The Mississippi Delta is about 130m thick above basal gravels – approximately the amount of sea level rise since the lows of the last ice age. The mechanism: – when sea level rises and floods up river, the river hits the still water of the sea earlier and drops its sediment thus building up the delta to match the sea level rise. Like the atoll, the delta responds to sea level rise to preserve itself – indeed it gets eroded away when sea level drops.
I remain somewhat suspicious of Topex/Poseidon, Jason etc. They had tremendous problems of calibration at the beginning and it is unclear how much of the ocean they cover,or even if it is possible to decide where the boundaries of “ocean” are.
What matters is the sea level in the vicinity of land surfaces and these measurements are subject to many uncertainties, particularly upwards biases. You have to ask which sea level do you want to know. What is important is the frequency that the sea intrudes into the land at various important places. Tide gauge measurements presumably do show the highest level, but they depend on what sort of equipment you use. I argue that severe storms tend to churn up the water near the gauge and give a spurious low figure for the average level. This gets used as an argument that all subsequent measurements show a rise.
This is yet another example in climate science where you never see the actual measurements, which would consist of daily fluctuations. These get averaged out with various levels of inaccuracy to give monthly records. But I am unclear that you ever get to see these, because they need to be “corrected” for isostasy, geological movement of many coastlines which woukl show some uncorrected data as inevitably rising and others inevitably falling. John Daly showed that these corrections were based on a small sample of mainly Northern Hemisphere examples and he questioned whather they could be applied everywhere.
Tide-gauge equpment gets a battering from the sea and it is difficilt to stop it from being forced down. When destroyed how can you restore it at the same level?. The recent introdiction of GPS equipment helps to solve this and I attribute the levelling off of many tide-gauge records to this alone. Then, most land surfaces are prone to subsidence from removal of minerals or water and from the weight of buildings. I am unaware that any “correction” has ever been made for this.
Finally, the most technologically sophisticated tide-gauge measurement project was carried out by the Australians on 12 Pacific islands from 1991 and, if you take into account what I say (which their authors do not) they show no sea level rise since then, particularly after GPS equipment was installed in 2000. I therefore argue that sea level, as measured close to land, where it actually matters, may not be rising at all..
Just want to add my thanks for a wonderful, readable article. Really warmed me up (despite the cold weather here)
And to add that File>Print>Print as PDF works in firefox too 😉
Willis,
Thanks for an extremely enlightening article. I knew most of the science of coral atolls already, but was not aware of the role of parrotfish or the effective remedial measures that would solve the problems created by recent human land-use and dredging practices. This deserves to be published in the MSM – in a worthy newspaper like the National Post, to educate and deprogram the general public and hopefully policy wonks and politicians.
Vincent Gray (14:09:26) – As always, Vincent, good to hear from you. For those who do not recognize the name, Vincent started the New Zealand Climate Coalition, and is a well-known author in the field.
What you say is true. However, what I used the data for was to show, not the absolute value, but the change in the value of the trend. I used it only to highlight the fact that sea level rise is not accelerating, it is decelerating.
I fear I lost you here. Whether the surface is “churned up” or not, the average level should stay the same, ceteris paribus. What am I missing here?
Restoring it to the same level is easy. I’ve seen the gauge here in Honiara. If it gets damaged, it can just be re-installed into the same boltholes into the concrete on the side of the main wharf …
In the long run, GPS is the answer to these problems. As you point out, for many years these adjustments were done using heuristic formulas with little factual underpinning. However, the advent of GPS allows very accurate measurement of vertical ground movement.
This is called the SEAFRAME project, which I mentioned above. They do take into account local ground subsidence (change of the height of the tidal station versus local landmarks. From the SEAFRAME document I cited above:
Unfortunately, the GPS stations were all installed around 2001 – 2003, so there is not enough data yet to give the absolute values. From the same SEAFRAME document:
Preliminary results of the GPS project are available at this link (1.1 Mb PDF), but as the website says, “It is important to note that the length of the time series is too short for reliable vertical station velocity estimation.”
I also don’t understand where you are getting the claim that the SEAFRAME project shows no sea level rise in the Pacific since 2000. Take a look at the SEAFRAME document I cited above for Tuvalu, it clearly shows a rise since 2000. Do you have a citation for your claim?
My best to you, Vincent, keep fighting the good fight,
w.
30/03/2002
GLOBAL WARMING NOT SINKING TUVALU –
– BUT MAYBE ITS OWN PEOPLE ARE
http://www.tuvaluislands.com/news/archived/2002/2002-03-30.htm
International environmentalists might have it wrong — global warming is not drowning the Pacific atoll nation of Tuvalu beneath a rising Pacific.
Its fate may be much more prosaic and all local: severe over-population, profound pollution and an unusual World War II legacy.
Experts even believe that if the threatening El Niño event occurs in the next six months, the sea level around Tuvalu will actually fall a by a dramatic 30 centimeters (11 inches). It did during the last big El Niño.
“The historical record shows no visual evidence of any acceleration in sea level trends,” Australia’s National Tidal Facility (NTF) said in a statement about Tuvalu this week.
Contrast that hard science with the emotional statement of Tuvalu Prime Minister Koloa Talake at last month’s Commonwealth Heads of Government meeting where he announced Tuvalu, its neighbor Kiribati and the Maldives are planning legal action against Western nations that they say are creating the global warming that is rising the Pacific’s level.
…
Reality Check, thanks for an interesting article I had never seen, and from 2002, no less. I loved this part:
I can understand that, I’ve received my own share of hate mail from Tuvalu myself …
Willis, I note your reply to Vincent Gray.
Please read my post. The document you have on Tuvalu was prepared by an NGO it is likely to be biased towards providing aid.
The project is not called Seaframe but SPSLCMP (South Pacific sea level and climate monitoring project) but they do use Seaframe instruments.
The Summary Report Jul08-jun09 issued by the National Tidal Centre of BOM is worth downloading because it has all the climate data back to 1991 (first phase of project 1991 to 2000) and some very good explanations about ENSO cycles, El Nino, earthquake effects etc.
If you can’t find it or do not have the time send me an email and I will attach it to my reply.
I am sure that you wiil be interested in the report. If you look at figure 10 (Monthly mean sea levels to june 2009) you will find that there has been no increase in sea levels at Tuvalu since 1999. That also applies for most of the other islands. In 2008 there was a reduction in sea levels.
Dear Willis
Good to meet somebody who has been there.
It is impossible to provide a “citation” to the literature as they have carefully stopped this from happening. The only source is the Australian BoM website and I suspect that they are prevented from publishing in the literature or revealing the names of the authors.
Until recently they have concealed the actual data which has obly been published in the individual island reports. My paper at
http://nzclimatescience.net/images/PDFs/spsl3.pdf
was the first to include all the sites and discuss them in detail. I argue that after they installed GPS there is no signiuficant change, and that the supposed “trends” are based on including the early teething troubles and the effects of the 1998 cyclone..I insist that the cyclone causes turbulence in the base of the equipment and a spurious low reading
I would welcome your comments.
The latest Monthly Report at
http://www.bom.gov.au/oceanography/projects/spslcmp/spslcmp.shtml
does have a graph with all the results and it is obvious that there is little opr no change for any of them. I am surprised that you have been able to find a “trend” for Tuvalu. Are you prepared to give 95% confidence limits for your figure?
The Summary Repoorts of the Australian Project are deliberately misleading as they only give “TRENDS” and conceal actual records. The latest Monthly Report Givews both, but these trens are based on the nistaken assumption that all the points are equivalent. Since 2000 the trend is mighty near zero.
Mitchell’s name is given, but who are the authors?
As to local sea level rises; in mid 2006, a British/Dutch team using a European polar orbit satellite, reported on ten years of observations of the sea level rise of the Arctic Ocean.
Their resulting measurments; which they say they have very high confidence in was that the Arctic ocean sea level over that decade, had been rising at a rate of -2 mm per year. This can alternatively be interpreted as an actual sea level fall of 2 mm per year.
As I said; they had high confidence in their observed results; but had no idea why that should be so; so they were waiting for the theoreticians to catch up, and explain their observations.
Actually, that had alread occurred about two years earlier in mid 2004, but it took till Jan 2005 for Physics Today, to publish my letetr in which I predicted that in fact sea levels would fall, as the floating sea ice melted.
My assertian was pooh-poohed by some notable AGW climatologists; one of whom simply asserted, that when you heated the oceans, the sea water expanded, so the water level rose.
The astute reader will instantly discern the connection between his warming of the oceans, and my argument as to the melting of the floating sea ice; come now, you have had plenty of time to see the connection.
You see, when the floating sea ice melts, most of that sea ice is actually under the ocean water, so the heat required to melt the ice; about 80 calories per gram, comes not from the atmosphere, or any sunlight, but directly from the sea water in contact with the ice.
So you could cool one gram of se water, by 80 deg C, or you could cool 80 grams, bu 1.0 deg C, or even 800 grams by 0.1 deg C; but basically, the melting of all that floating sea ice results in the lowering of the temperature, of an astronomical amount of sea water. Add to that the trivia information, that sea water with more than 2.47% salinity, has no maximum density before its freezing point. Since most sea water is about 3.5% salinity, that means that sea water always has a positive temperature coefficient of expansion, down to its freezing point, and therefore the cooling of all that ocean water increases the density, and lowers the sea level due to contraction.
iot is left as an exercise to the astute reader to show, that if one assumes that the TC of the ocean water is quite constant at those temperatures (probably isn’t); that the shrinkage of the surface level is pretty much independent of how much water cools; so you don’t have to know anything about the temperature gradient as the ice melts. If you cool a double height water column by only half the temperature drop, the total height contraction stays the same; but note my caveat, that the TC is likely not ecxactly constant over thsoe temperature ranges; and no I don’t have the foggiest idea what it actually is.
Of course a key result of my assertion, and the British/Dutch research team’s observations, is that it really did establish, that over those ten years of their observations from about 1996-2006, the total ice floating in the arctic ocean was in fact diminishing, asd the alarmists were happy to point out; well until the fall 2007 minimum anyway.
So Nyet, on sea levels rising everywhere, sometimes, some places, it goes the other way.
And if someone asserts that simple physics requires the sea to shrink, when floating sea ice melts; don’t respond with an inane comment like; everyone knows if you heat the ocean water it expands. What does that have to do with the floating se ice melting ?
Excellent article as always, Willis.
I’m familiar with the water problems from reading a really entertaining travelogue called The Sex Lives of Cannibals by J. Maarten Troost.
Maarten and his wife were sent to Tarawa in the island nation of Kiribati [just across the equator from Tuvalu – a different country]. They describe a lot of the same problems, like the disappearing water lens. Vegetables can’t be grown in most places due to salt water intrusion.
Overpopulation is the central problem. Some of the 33 atolls that comprise the country are less than 200 yards across, and have thousands of people living on them. Pollution is very bad.
The governments of all the South Sea island nations [Tuvalu, Fiji, Tonga, etc.] have learned to play the global warming/rising sea level game. If it weren’t for international aid, Kiribati wouldn’t survive. Its last worthwhile export was phosphate [seabird guano]. When the guano islands gave out, the UK wisely
cut them loosegranted them independence. There are probably few worse places to live.With any luck the sea level will rise fast, and the people will have to be relocated to Australia or somewhere else above high tide. But since the sea level isn’t rising faster than the coral grows, they appear to be SOL.
Willis and Vincent,
The latest (to Jun2009) South Pacific report is here http://www.bom.gov.au/oceanography/projects/spslcmp/reports_6mths.shtml
It is worth downloading for anyone interested in climate cycles.
Vincent Gray (16:22:59), you say:
I believe the document you refer to is THE SOUTH PACIFIC SEA LEVEL & CLIMATE MONITORING PROJECT MONTHLY DATA REPORT NO. 174 DECEMBER 2009. It is available here.
On page 4 of that report, it gives the currently measured rate of sea level rise for Tuvalu as 5.1mm/yr. Per the Tuvalu report I cited above, the 95% CI for this is on the order of ±4 mm/yr. This is because we only have 17 years of data, far too short for good accuracy.
What am I missing here? I get the feeling we’re not talking about the same thing, I just can’t figure out where …
w.
George E. Smith (17:59:55) : edit
Citation? I’m not going to waste my time trying to guess which study you are referring to.
w.