Meeresspiegelentwicklung in Ostsee und Nordsee durch 70-jährigen Ozeanzyklus gepulst

Immer wieder warnen uns einzelne Forscher vor einer ihrer Meinung nach bevorstehenden enormen Steigerung des Meeresspiegelanstiegs. Denn nur wenn sich die Raten steigern, können die vorgeschlagenen Sintflut-Szenarien Wirklichkeit werden. Küstenpegelmessungen werden seit mehr als 100 Jahren durchgeführt. Gibt es hier vielleicht bereits Anzeichen, dass das Meer schneller steigt als zuvor? Phil Watson von der University of New South Wales hat die europäischen Pegeldaten mit einer neuen Software analysiert, die besonders Trends hervorhebt. Das Ergebnis ist deutlich: Bislang ist keine Spur von einer Beschleunigung in den Daten zu erkennen. Es wird wohl noch weitere 20 Jahre brauchen, bis man diese Frage überhaupt klären könnte, erläutert der Autor. Sämtliche Anstiegsraten liegen unterhalb des globalen Satellitendurchschnitts von 3,4 mm /Jahr. Hier der Abstract der Arbeit, die im Januar 2017 im Journal of Coastal Research erschien:

Acceleration in European Mean Sea Level? A New Insight Using Improved Tools
Research into sea-level rise has taken on particular prominence in more recent times owing to the global threat posed by climate change and the fact that mean sea level and temperature remain the key proxies by which we can measure changes to the climate system. Under various climate change scenarios, it has been estimated that the threat posed by the effects of sea-level rise might lead to annual damage costs across Europe on the order of €25 billion by the 2080s. European mean sea-level records are among the best time series data available globally by which to detect the presence of necessary accelerations forecast by physics-based projection models to elevate current rates of global sea-level rise (≈3 mm/y) to anywhere in the vicinity of 10–20 mm/y by 2100. The analysis in this paper is based on a recently developed analytical package titled “msltrend,” specifically designed to enhance estimates of trend, real-time velocity, and acceleration in the relative mean sea-level signal derived from long annual average ocean water level time series. Key findings are that at the 95% confidence level, no consistent or compelling evidence (yet) exists that recent rates of rise are higher or abnormal in the context of the historical records available across Europe, nor is there any evidence that geocentric rates of rise are above the global average. It is likely a further 20 years of data will distinguish whether recent increases are evidence of the onset of climate change–induced acceleration.

Für die Arktis der letzten 60 Jahre präsentierten Svendsen et al. im August 2016 eine Küstenpegelsynthese. Sie fanden einen Anstiegstrend von 1,5 mm pro Jahr.

Stable reconstruction of Arctic sea level for the 1950–2010 period
Reconstruction of historical Arctic sea level is generally difficult due to the limited coverage and quality of both tide gauge and altimetry data in the area. Here a strategy to achieve a stable and plausible reconstruction of Arctic sea level from 1950 to today is presented. This work is based on the combination of tide gauge records and a new 20 year reprocessed satellite altimetry-derived sea level pattern. Hence, the study is limited to the area covered by satellite altimetry (68°N and 82°N). It is found that time step cumulative reconstruction as suggested by Church and White (2011) may yield widely variable results and is difficult to stabilize due to the many gaps in both tide gauge and satellite data. A more robust sea level reconstruction approach is to use datum adjustment of the tide gauges in combination with satellite altimetry, as described by Ray and Douglas (2011). In this approach, a datum-fit of each tide gauges is used and the method takes into account the entirety of each tide gauge record. This makes the Arctic sea level reconstruction much less prone to drifting. From our reconstruction, we found that the Arctic mean sea level trend is around 1.5 mm ± 0.3 mm/yr for the period 1950–2010, between 68°N and 82°N. This value is in good agreement with the global mean trend of 1.8 ± 0.3 mm/yr over the same period as found by Church and White (2004).

Schon gewusst? Teile Dänemarks kämpften in den letzten Jahrausenden mit einem fallenden Meeresspiegel. Hede et al. 2015:

Changes in Holocene relative sea-level and coastal morphology: A study of a raised beach ridge system on Samsø, southwest Scandinavia
[...] After c. 3500 yr BP, the [relative sea level curve] curve shows a gradual decrease at a rate of c. 0.6 mm/yr.

Kuijpers et al. 2012 beschreiben eine Meeresspiegelabsenkung nach der Mittelalterlichen Wärmeperiode in ihrem dänischen Studiengebiet in Seeland. Eine ähnliche Absenkung im Zuge der Kleinen Eiszeit nehmen auch Hansen et al. 2012 für die Nordsee und Ostesee an. Sie dokumentieren zudem eine Zyklizität mit einer Periodendauer von 70 Jahren, was vermutlich den bekannten Ozeanzyklen entspricht. Phasen der Beschleunigung müssen zwingend im Kontext dieser Zyklik gesehen werden. Die natürliche Anstiegsrate Ende des 18. Jahrhunderts am Ende der Kleinen Eiszeit überstieg die heutige sowie alle Prognosen des 21. Jahrhunderts. Hier der Abstract der Arbeit aus Boreas:

Absolute sea levels and isostatic changes of the eastern North Sea to central Baltic region during the last 900 years
Most studies of late Holocene sea-level changes generally assume stable tectonic conditions. However, unrecognized neotectonic ‘noise’, even the small rates of passive continental margins, can severely distort sea-level reconstructions of the late Holocene. The detailed sea-level curve proposed here is reconstructed by identification of an area (Læsø archipelago in the Kattegat Sea) where small neotectonic level changes and other kinds of ‘background noise’ can be precisely quantified by advanced LiDAR techniques. We show that the absolute (‘eustatic’) sea level of Kattegat has risen by 110±14 cm since AD 1300 and that the Little Ice Age lowstand occurred between 1250 and 1750. Thereafter, four oscillations with a cyclicity of ∼70 years peaked around 1790, 1860, 1920–1950 (double peak), and at the present. We discuss the global implications of the curve, for example that the acceleration in the present sea-level rise may be part of this 70-year cyclicity, and that the non-anthropogenic sea-level rise between 1700 and 1790 seems faster than the present and projected sea-level rise for the 21st century. Moreover, the conspicuous sea-level fall at the beginning of the Little Ice Age confirms that ice-cap growth can be faster than ice-cap melting. By comparison with 29 long-term tide gauge measurements of the region we show that the isostatic implications of the sea-level curve are in nearly perfect agreement with Peltier’s global isostatic VM2 model (applied by IPCC and PSMSL) and yield a 3–4 times smaller spread of isostatic rates. Owing to this higher precision it is possible to produce a reliable isostatic map of SW Scandinavia, Denmark, N Germany and NW Poland. This new map identifies an isostatic jump by ∼0.6 mm a−1 at the Ringkøbing-Fyn Basement High, separating the isostatic pattern of the North German Basin from the isostatic pattern of the Danish Basin and the Scandinavian Peninsula.