Südseeträumereien: Märchenstunde mit Onkel Schellnhuber

Hans Joachim Schellnhuber hat das Potsdam-Institut für Klimafolgenforschung (PIK) mitgegründet und steht ihm als Direktor vor. Seine klimaalarmistische Handschrift prägt die Strategie des Instituts: Laut trommeln um schnellstmöglich die Deindustralisierung Deutschlands zu erzielen. Eines muss man Schellnhuber lassen: Er ist ein rhetorisch begabter Redner, wählt geschickte Formulierungen, um zu überzeugen. Am 22. April 2017 konnte man wieder einmal eine Kostprobe seines Könnens im Radio bestaunen. RBB-RadioEins befragte ihn zum Klimawandel. Darin erklärt er, er habe die Klimaskeptiker aufgegeben, die wären ihm zu dumm, mit denen könne man nicht vernünftig reden. Gegen Ende des 5-minütigen Interviews wird er vom Radiojournalisten gefragt, wie Schellnhuber einem Laien am besten die große und reale Gefahr des Klimawandels beweisen würde. Der geschickte PIK-Chef ist auf solche Fragen natürlich bestens vorbereitet. Er bringt ein schauriges Beispiel aus der Südsee, wo der menschengemachte Klimawandel bereits in hinterhältigerweise die Friedhöfe von Palmeninseln überflutet habe. In einigen Fällen schaut nur noch das Kreuz aus dem Wasser. Ein Dreipunktewurf für Schellnhuber. Der Radiohörer kann gar nicht anders und glaubt Schellnhuber sogleich aufs Wort. Recht hat der Mann!

Es muss ja so sein, denn Schellnhuber ist Kanzlerinnen- und Papstberater in Sachen Klimawandel. Der kann gar nicht falschliegen. Aus einem Bauchgefühl heraus googlen wir trotzdem einmal die Kombination „Friedhof“, „Südsee“, „Klimawandel“, „Meeresspiegelanstieg“. Wo genau liegen diese Klimawandel-Beweis-Friedhöfe?

Wir werden bei der New York Times fündig, die 2015 das makabre Thema vorlegte:

He [Tony A. deBrum, the foreign minister of the Marshall Islands] envisions elevating Marshallese cities as much as six feet and building resilient new drainage systems. “That could buy us at least 20 years,” he said. For now, on Majuro, the Marshall Islands’ capital, the adaptation to sea-level rise is lower tech. In the neighborhood of Jenrok, a seaside cemetery has been eroded by the rising waves — about 10 rows of coffins and headstones have washed out to sea. To adapt, the Marshallese encase their dead in aboveground concrete tombs, but the rising waves have started to lap at those, too.

Es stimmt also, auf den Marshallinseln nagt das Meer an Friedhöfen. Schellnhuber hatte Recht. Aber steckt wirklich der Klimawandel und der menschengemachte Meeresspiegelanstieg dahinter? Immerhin könnte es sich um ganz normale Küstenerosion handeln. Die findet nämlich auch ganz ohne Meeresspiegelanstieg statt. Prüfen wir also zunächst, wie sich der Meeresspiegel im Bereich der Marshall-Inseln in den letzten Jahrhunderten entwickelt hat. Dabei stoßen wir auf Forschungsresultate von Paul Kench und Kollegen, die im Februar 2014 in den Geophysical Research Letters erschienen sind. Was für eine Überraschung: Der Meeresspiegel auf der Inselgruppe hat sich in den letzten 2000 Jahren um einen Meter abgesenkt (Abbildung 1).

Abbildung 1: Meeresspiegelentwicklung auf den Marschallinseln während der vergangenen 6000 Jahre. Quelle: Kench et al. 2014.


Hier die Kurzfassung der Arbeit:

Evidence for coral island formation during rising sea level in the central Pacific Ocean
The timing and evolution of Jabat Island, Marshall Islands, was investigated using morphostratigraphic analysis and radiometric dating. Results show the first evidence of island building in the Pacific during latter stages of Holocene sea level rise. A three-phase model of development of Jabat is presented. Initially, rapid accumulation of coarse sediments on Jabat occurred 4800–4000 years B.P. across a reef flat higher than present level, as sea level continued to rise. During the highstand, island margins and particularly the western margin accreted vertically to 2.5–3.0 m above contemporary ridge elevations. This accumulation phase was dominated by sand-size sediments. Phase three involved deposition of gravel ridges on the northern reef, as sea level fell to present position. Jabat has remained geomorphically stable for the past 2000 years. Findings suggest reef platforms may accommodate the oldest reef islands in atoll systems, which may have profound implications for questions of prehistoric migration through Pacific archipelagos.

Das Science Magazin fand die Studie so bedeutsam, dass sie sie in einem eigenen Beitrag von Christopher Pala besprechen ließ:

Studies suggest that atoll islands will rise in step with a rising sea
By Christopher Pala, on South Tarawa

As the minibus wobbles over the dusty, pothole-filled road that runs the length of South Tarawa island, a song blasting over Kiribati’s state radio envisions an apocalypse for this fishhook-shaped atoll halfway between Honolulu and Fiji: “The angry sea will kill us all.” The song, which won a competition organized by Kiribati’s government, reflects the views of President Anote Tong, who has been warning for years of a knockout punch from climate change. […] No doubt, the sea is coming: In a 2013 report, the U.N. Intergovernmental Panel on Climate Change predicted that global sea levels will rise up to 1 meter by 2100. But recent geologic studies suggest that the coral reefs supporting sandy atoll islands will grow and rise in tandem with the sea. The only islanders who will have to move must do so for the same reason as millions of people on the continents: because they live too close to shore.

Paul Kench, a geomorphologist who now heads the University of Auckland’s School of Environment in New Zealand, was the first to question the dire forecasts for Kiribati and similar island nations. In 1999, the World Bank asked him to evaluate the economic costs of sea-level rise and climate change to Pacific island nations. Kench, who had been studying how atoll islands evolve over time, says he had assumed that a rising ocean would engulf the islands, which consist of sand perched on reefs. “That’s what everyone thought, and nobody questioned it,” he says. But when he scoured the literature, he could not find a single study to support that scenario.

So Kench teamed up with Peter Cowell, a geomorphologist at the University of Sydney in Australia, to model what might happen. They found that during episodes of high seas—at high tide during El Niño events, which raise sea level in the Central Pacific, for example—storm waves would wash over higher and higher sections of atoll islands. But instead of eroding land, the waves would raise island elevation by depositing sand produced from broken coral, coralline algae, mollusks, and foraminifera.

Kench notes that reefs can grow 10 to 15 mill imeters a year—faster than the sea-level rise expected to occur later this century. “As long as the reef is healthy and generates an abundant supply of sand, there’s no reason a reef island can’t grow and keep up,” he argues. This equilibrium may not mean that all areas of atolls will remain habitable, says Scott Smithers, a geomorphologist at James Cook University, Townsville, in Australia. “The changes might happen at a rate that exceeds the recovery,” he says. But the geologic record is reassuring, Kench and others found when they drilled deep cores into reef islands to probe how they responded to past sea-level changes. In a February report in Geophysical Research Letters, the researchers found that the island of Jabat in the Marshall Islands emerged on a reef 4800 to 4000 years ago, when sea levels were rising as fast as they are expected to rise over the next century. Other support for the model has come from monitoring how shorelines respond to seasonal […]

Vanua Levu in Fiji is a less appealing refuge. The purchase was “a publicity stunt,” scoffs Teburoro Tito, a former president of Kiribati and member of the opposition party Protect the Maneaba. Already home to 270 farmers from the Solomon Islands, the steep, hilly tract may accommodate only a few hundred more people. If the optimists are right, no one from Kiribati will have to leave their country anyway.

Ganzen Artikel hier lesen.

Im Online Magazin The Conversation fasste Paul Kench im April 214 seine hochinteressanten Forschungsresultate für die Öffentlichkeit selber zusammen. Hier ein Auszug mit Erkenntnissen zu den Marschallinseln aus dem lesenswerten Artikel:

Dynamic atolls give hope that Pacific Islands can defy sea rise
[…] Another of our studies found that islands in Nadikdik Atoll, Marshall Islands, have been rebuilt over the past century despite being destroyed by a typhoon in 1905. All of this shows that reef islands are able to grow under current climate conditions. This suggests that coral islands are very dynamic landforms that adjust their shape and position on reef surfaces over decades. Low-lying islands are built by the action of waves and currents, which deposit sand and gravel at the shoreline. Just like any beach, as wave and current processes change, island sand and shingle is mobilised and deposited elsewhere on the shoreline. Through this ongoing process islands can change their shape and migrate across reef surfaces. We are now aiming to work out the scale and speed of these changes – which will be crucial for helping island communities to adapt to the rising seas. One question is whether islands can build vertically to keep pace with rising sea levels. Our results suggest that islands can grow upwards when waves wash over them during storms or tsunami, depositing sand in the process. This suggests that islands may be able to withstand rising sea levels and increased storminess – although life on those islands may be very different to today. On the face of it, this is potentially good news for Pacific communities. The islands they call home may be less vulnerable than is commonly thought. But our findings also suggest that although the islands may not be swamped by rising seas, they are likely to change in size and shift their position on the surface of reefs. The rate of these changes may also increase as sea level rises. This raises questions for their ongoing habitation. How will physical changes to the islands affect drinking water supplies, and how will communities need to adapt their farming practices? Questions about island change must be addressed urgently in order to inform decision making and secure the future of Pacific nations.

Ganzen Artikel auf The Conversation lesen.

Viele Jahre lang hatten Klimaalarmisten große Freude an einem der Küstenpegel-Messstellen auf den Marshall-Inseln. Der Pegel Kwajalein schien in den letzten Jahren einen beschleunigten Anstieg anzuzeigen. Um 2015 dann die große Ernüchterung: Der Meeresspiegel sagte plötzlich rapide um 15 cm ab. Ende des Alarms. Kürzlich stieg der Meeresspiegel wieder an. Es wird klar: Hier spielen natürliche Faktoren wie die ENSO und El Nino eine große Rolle. Im Mittel der letzten Jahrzehnte stieg der Meeresspiegel in Kwajalein um 2,2 mm pro Jahr, was dem weltweiten Durchschnitt entspricht. Im Maßstab von Jahrhunderten sehen wir bedeutende Oszillationen (siehe oben), die viel größere Auswirkungen hatten. Schellnhuber schweigt sich zu dieser unbequemen natürlichen Meeresspiegeldynamik aus.

Abbildung: Entwicklung des Meeresspiegels am Pegel Kwajaleon, Marshall Inseln, Pazifik. Quelle: NOAA



Was steckt also wirklich hinter der Küstenerosion auf den Marshall-Inseln? Vieles deutet auf andere anthopogene Ursachen hin, nämlich den Raubbau an der Natur. Auf den Inseln und an der Küste wird kräftig gebaggert, planiert, asphaltiert, Strömungen verändert, was pures Gift für die anfälligen Koralleninseln ist. Beispiel Xue 2001:

Coastal Erosion and Management of Majuro Atoll, Marshall Islands
About fifty kilometers of lagoon coast in Majuro Atoll is suffering erosion, which is induced by human activities including aggregate excavating and building causeways, artificial channels, landfill and other constructions. The west longshore sediment transportation on lagoon coast is significant for stability of lagoon shore of the west atoll. The lagoon coast erosion on the west atoll is induced by development on the east atoll. Distribution of beachrock demonstrates former existence of a continuous land on the south rim. The causeway has not caused sea level rising in lagoon. Openings on the south rim should not be made, as these will induce severe erosion. Reforming lagoon coastal constructions is proposed.

Das Problem besteht auch heute noch weiter, wie Tai Huang & Henrik Rapp 2010 am Beispiel eines anderen Eilands der Marshall Inseln, des Majuro Atolls, darlegten:

4.1.3 Possible causes of coastal erosion on Majuro
The above-discussed causes of erosion can all be observed on Majuro. Hard coastal structures, especially seawalls, are likely to be one of the major causes for the recent changes in sediment transport patterns. Sandy beaches are nowadays only found in a few places on Majuro. Material used for constructions is not easily obtained on Majuro and up until recently material has been taken from quarries on both the lagoon and ocean side. Recent studies from SOPAC have shown a worrying increase in the erosion as a result of the dredging, mostly visible on Laura where sandy beaches previously were in abundance. Sand material is also commonly taken from the beach by locals to be used as filling material for various purposes. Educational efforts have been made by EPA by implementing environmental awareness programs and to teach locals about the possible effects of removal of sand material from the beach. Still, sand material remains a scarce and valuable resource, very much available for anyone to take.

Hans Joachim Schellnhuber gaukelt uns also vor, die Klimaerwärmung wäre das Hauptproblem der Pazifikinseln. In Wirklichkeit ist es unvernünftiges Verhalten; die Bevölkerung sägt sich quasi selber den Ast ab, auf dem sie sitzt. Das ist übrigens kein Grund für Schadenfreude. Denn wir Deutschen haben das selber schon getan. Auf der Nordseeinsel Helgoland verkaufte man lange Zeit Baumaterial aus Inselsteinbrüchen nach Hamburg. Die ehemalige Verbindung zwischen Hauptinsel und Düne wurde dabei immer schmaler und brüchiger. Einer der berüchtigten Nordseestürme fegte schließlich die Reste hinweg und trennte die beiden heutigen Einzelinseln. Kurzsichtiges Verhalten rächt sich irgendwann. Allerdings zeigten sich die Insulaner erfinderisch und schlugen aus der Situation sogleich wieder Profit. Mit den kleinen Börtebooten werden heute Touristen zwischen Hauptinsel und Düne transportiert, eine unerschöpfliche und im Gegensatz zum Gesteinsabbau nachhaltige Einnahmequelle…