Vor 4000 Jahren lag der Meeresspiegel in Brasilien drei Meter höher als heute

Der globale Meeresspiegel ist seit 1958 um 1,5 mm pro Jahr angestiegen, fanden Frederiske et al. 2018:

A Consistent Sea-Level Reconstruction and Its Budget on Basin and Global Scales over 1958–2014

Different sea level reconstructions show a spread in sea level rise over the last six decades and it is not yet certain whether the sum of contributors explains the reconstructed rise. Possible causes for this spread are, among others, vertical land motion at tide-gauge locations and the sparse sampling of the spatially variable ocean. To assess these open questions, reconstructed sea level and the role of the contributors are investigated on a local, basin, and global scale. High-latitude seas are excluded. Tide-gauge records are combined with observations of vertical land motion, independent estimates of ice-mass loss, terrestrial water storage, and barotropic atmospheric forcing in a self-consistent framework to reconstruct sea level changes on basin and global scales, which are compared to the estimated sum of contributing processes. For the first time, it is shown that for most basins the reconstructed sea level trend and acceleration can be explained by the sum of contributors, as well as a large part of the decadal variability. The sparsely sampled South Atlantic Ocean forms an exception. The global-mean sea level reconstruction shows a trend of 1.5 ± 0.2 mm yr−1 over 1958–2014 (1σ), compared to 1.3 ± 0.1 mm yr−1 for the sum of contributors. Over the same period, the reconstruction shows a positive acceleration of 0.07 ± 0.02 mm yr−2, which is also in agreement with the sum of contributors, which shows an acceleration of 0.07 ± 0.01 mm yr−2. Since 1993, both reconstructed sea level and the sum of contributors show good agreement with altimetry estimates.

Laut Hay et al. 2015 stieg der globale Meeresspiegel zwischen 1901 und 1990 um 1,2 mm pro Jahr und um 3,0 mm pro Jahr zwischen 1993-2010.  

Aber hat sich der Meeresspiegelanstieg in den letzten Jahrzehnten wirklich beschleunigt? Willis Eschenbach hat hier seine Bedenken. Seltsamerweise begann die Beschleunigung nämlich genau, als die Satellitenmessungen begannen…

Judith Curry diskutierte in ihrem Blog umfassend den Meeresspiegelanstieg. Für alle die es genauer wissen wollen, ein absolutes Lesemuss:

Teil 1: Introduction

Teil 2: The geological record

Teil 3: 19th & 20th century observations

Teil 4: Satellite era record

Teil 5: Detection & attribution

Teil 6: Projections for the 21st century

Currys Gesamtbericht zum Meeresspiegel hier. Die Washington Times berichtete über den Bericht.

In Teil 4 schreibt sie:

Satellite measurements of global sea level have been available since 1992, and the technology is under continuing development. Complex analysis methods are required to transform raw satellite measurements into sea level variations, including the correction and piecing together of records collected over many years by ageing and changing satellites. Estimates of sea level change made using satellite-collected data are associated with many uncertainties in the data processing; with time, the uncertainty in current analysis methods and datasets may be revised as addition errors are uncovered. There is some inconsistency between the results derived by different research groups for the interannual variability, owing to differences in making the complex adjustments. These uncertainties underscore the need for continual scrutiny of the satellite and in situ tide gauge data, plus the need for independent observing systems such as multiple satellite altimeters with differing instrument designs, the tide gauge network, in situ ocean temperature observing system, and gravimetric satellites.

Bis zur Hälfte der Erwärmung und des Meeresspiegelanstiegs im Atlantik in niederen und mittleren Breiten geht wohl auf natürliche Ursachen zurück, schreibt die University of Oxford am 7.1.2019 (via Science Daily):

A century and half of reconstructed ocean warming offers clues for the future

Due to a scarcity of data, most global estimates of ocean warming start only in the 1950s. However, a team of scientists has now succeeded in reconstructing ocean temperature change from 1871 to 2017.

Over the past century, increased greenhouse gas emissions have given rise to an excess of energy in the Earth system. More than 90% of this excess energy has been absorbed by the ocean, leading to increased ocean temperatures and associated sea level rise, while moderating surface warming.

The multi-disciplinary team of scientists have published estimates in PNAS, that global warming of the oceans of 436 x 1021 Joules has occurred from 1871 to present (roughly 1000 times annual worldwide human primary energy consumption) and that comparable warming happened over the periods 1920-1945 and 1990-2015. The estimates support evidence that the oceans are absorbing most of the excess energy in the climate system arising from greenhouse gases emitted by human activities.

Prof Laure Zanna (Physics), who led the international team of researchers said: ‚Our reconstruction is in line with other direct estimates and provides evidence for ocean warming before the 1950s.‘ The researchers‘ technique to reconstruct ocean warming is based on a mathematical approach originally developed by Prof Samar Khatiwala (Earth Sciences) to reconstruct humanmade CO2 uptake by the ocean.

Prof Khatiwala said: ‚Our approach is akin to „painting“ different bits of the ocean surface with dyes of different colors and monitoring how they spread into the interior over time. We can then apply that information to anything else — for example humanmade carbon or heat anomalies — that is transported by ocean circulation. If we know what the sea surface temperature anomaly was in 1870 in the North Atlantic Ocean we can figure out how much it contributes to the warming in, say, the deep Indian Ocean in 2018. The idea goes back nearly 200 years to the English mathematician George Green.‘

The new estimate suggests that in the last 60 years up to half the observed warming and associated sea level rise in low- and mid- latitudes of the Atlantic Ocean is due to changes in ocean circulation. During this period, more heat has accumulated at lower latitudes than would have if circulation were not changing. While a change in ocean circulation is identified, the researchers cannot attribute it solely to human-induced changes.

Much work remains to be done to validate the method and provide a better uncertainty estimate, particularly in the earlier part of the reconstruction. However the consistency of the new estimate with direct temperature measurements gives the team confidence in their approach.

Prof Zanna said: ‚Strictly speaking, the technique is only applicable to tracers like humanmade carbon that are passively transported by ocean circulation. However, heat does not behave in this manner as it affects circulation by changing the density of seawater. We were pleasantly surprised how well the approach works. It opens up an exciting new way to study ocean warming in addition to using direct measurements.‘

This work offers an answer to an important gap in knowledge of ocean warming, but is only a first step. It is important to understand the cause of the ocean circulation changes to help predict future patterns of warming and sea level rise.

Paper: Laure Zanna, Samar Khatiwala, Jonathan M. Gregory, Jonathan Ison, and Patrick Heimbach. Global reconstruction of historical ocean heat storage and transport. PNAS, 2019 DOI: 10.1073/pnas.1808838115

Im mittleren Holozän war es wärmer als heute, und der Meeresspiegel war in einigen Teilen der Erde auch höher als heute. Der Geologe David Middleton ist auf WUWT dem Phänomen nachgegangen. In einem weiteren Artikel beleuchtet der Geowissenschaftler die Meeresspiegelentwicklung der letzten 300 Jahre.

Suguio et al. 2013 beschäftigten sich mit dem Meeresspiegelanstieg in Brasilien während der letzten 10.000 Jahre. Nach der letzten Eiszeit erreichte der Meeresspiegel vor 7400 Jahren das heutige Niveau. In der Zeit 5000-4000 Jahre vor heute lag der Meeresspiegel 3 m über der heutigen Marke, um danach langsam oszillierend auf den heutigen Stand abzusinken:

Indicators of Holocene sea level changes along the coast of the states of Pernambuco and Paraíba, Brazil

This study deals with the Holocene relative sea level (RSL) changes along the Brazilian northeastern coast, in particular along the states of Pernambuco and Paraíba. It presents 25 sea level superficial indicators, dominantly of a biological nature (i.e., vermetid gastropod tubes encrusted on rocky surfaces, as well as mollusk shells in live positions contained within beachrocks and paleomangrove deposits). Moreover, diatomological and palynological analyses have been carried out on a drilling core obtained from the Olhos d’Água lagoon (Southeastern Recife, Pernambuco state) with a length of about 2.7 m and age of about 8,300 cal yr BP at the base. The envelope RSL change curve obtained through the interpretation of the data indicates that, after reaching the current level ~ 7,400 cal yr BP, a sea level culmination of ~ 3 m above sea level was attained between 4,000 – 5,000 cal yr BP, and a general trend of sea level drop occurred until the present, with possible phases of slight oscillations. This is consistent with the oscillation frequency of microscopic marine and freshwater organisms in the sediment core.

Wieviel trägt der Antarktische Eisschild zum globalen Meeresspiegelanstieg in den kommenden 100 Jahren bei? Laut Schlegel et al. 2018 kann man die extremen Szenarien getrost ignorieren:

Exploration of Antarctic Ice Sheet 100-year contribution to sea level rise and associated model uncertainties using the ISSM framework

Estimating the future evolution of the Antarctic Ice Sheet (AIS) is critical for improving future sea level rise (SLR) projections. Numerical ice sheet models are invaluable tools for bounding Antarctic vulnerability; yet, few continental-scale projections of century-scale AIS SLR contribution exist, and those that do vary by up to an order of magnitude. This is partly because model projections of future sea level are inherently uncertain and depend largely on the model’s boundary conditions and climate forcing, which themselves are unknown due to the uncertainty in the projections of future anthropogenic emissions and subsequent climate response. Here, we aim to improve the understanding of how uncertainties in model forcing and boundary conditions affect ice sheet model simulations. With use of sampling techniques embedded within the Ice Sheet System Model (ISSM) framework, we assess how uncertainties in snow accumulation, ocean-induced melting, ice viscosity, basal friction, bedrock elevation, and the presence of ice shelves impact continental-scale 100-year model simulations of AIS future sea level contribution. Overall, we find that AIS sea level contribution is strongly affected by grounding line retreat, which is driven by the magnitude of ice shelf basal melt rates and by variations in bedrock topography. In addition, we find that over 1.2 m of AIS global mean sea level contribution over the next century is achievable, but not likely, as it is tenable only in response to unrealistically large melt rates and continental ice shelf collapse. Regionally, we find that under our most extreme 100-year warming experiment generalized for the entire ice sheet, the Amundsen Sea sector is the most significant source of model uncertainty (1032 mm 6σ spread) and the region with the largest potential for future sea level contribution (297 mm). In contrast, under a more plausible forcing informed regionally by literature and model sensitivity studies, the Ronne basin has a greater potential for local increases in ice shelf basal melt rates. As a result, under this more likely realization, where warm waters reach the continental shelf under the Ronne ice shelf, it is the Ronne basin, particularly the Evans and Rutford ice streams, that are the greatest contributors to potential SLR (161 mm) and to simulation uncertainty (420 mm 6σ spread).