Er vandstanden i verdenshavene accelererende?

Jeg har flere gange fundet, at vandstanden er accelerende ved analyse af enkelte tidevandsstationer, som f.eks. Stockholm 1774-2013. Jeg har ikke kunnet konstatere acceleration af vandstanden ud fra satellit data fra Colerado University. Dette skyldes formodentlig en for kort tidshorisont i sammenhæng med størrelsen af den forventede acceleration og forskellige månecykler dvs. 8.85 og 18.6 års cykleren.

Abstract
Projection of future sea level change relies on the understanding of present sea-level trend and how it has varied in the past. Here we investigate the global-mean sea level (GMSL) change during 1993–2012 using Empirical Mode Decomposition, in an attempt to distinguish the trend over this period from the interannual variability. It is found that the GMSL rises with the rate of 3.2 ± 0.4 mm/yr during 1993–2003 and started decelerating since 2004 to a rate of 1.8 ± 0.9 mm/yr in 2012. This deceleration is mainly due to the slowdown of ocean thermal expansion in the Pacific during the last decade, as a part of the Pacific decadal-scale variability, while the land-ice melting is accelerating the rise of the global ocean mass-equivalent sea level. Recent rapid recovery of the rising GMSL from its dramatic drop during the 2011 La Niña introduced a large uncertainty in the estimation of the sea level trend, but the decelerated rise of the GMSL appears to be intact.

Enhver ædruelig geolog må også mene, at mange storbyer og store dele af Danmark vil bliver oversvømmet på langt sigt. En vandstandsstigning på en 1 meter vil være til at håndtere, men 25 meter vil være et problem[...]Geologer må blive skræmt!
Det bemærkes, at geologer må bliver skræmt mht. fremtidige vandstandsstigninger blot ved en temperaturstigning på 2 °Celcius, idet en ligevægtsvandstand ved 2 °Celcius ligger på en vandstand på 25 meter højere end i dag. Denne vandstand nås efter tusinder af år.

This paper assesses historic changes in mean sea level around the coastline of the North Sea, one of the most densely populated coasts in the world. Typically, such analyses have been conducted at a national level, and detailed geographically wider analyses have not been undertaken for about 20 years. We analyse long records (up to 200 years) from 30 tide gauge sites, which are reasonably uniformly distributed along the coastline, and: (1) calculate relative sea level trends; (2) examine the inter-annual and decadal variations; (3) estimate regional geocentric (sometimes also referred to as 'absolute') sea level rise throughout the 20th century; and (4) assess the evidence for regional acceleration of sea-level rise. Relative sea level changes are broadly consistent with known vertical land movement patterns. The inter-annual and decadal variability is partly coherent across the region, but with some differences between the Inner North Sea and the English Channel. Data sets from various sources are used to provide estimates of the geocentric sea level changes. The long-term geocentric mean sea level trend for the 1900 to 2011 period is estimated to be 1.5 ± 0.1 mm/yr for the entire North Sea region. The trend is slightly higher for the Inner North Sea (i.e. 1.6 ± 0.1 mm/yr), and smaller but not significantly different on the 95% confidence level for the English Channel (i.e. 1.2 ± 0.1 mm/yr). The uncertainties in the estimates of vertical land movement rates are still large, and the results from a broad range of approaches for determining these rates are not consistent. Periods of sea level rise acceleration are detected at different times throughout the last 200 years and are to some extent related to air pressure variations. The recent rates of sea level rise (i.e. over the last two to three decades) are high compared to the long-term average, but are comparable to those which have been observed at other times in the late 19th and 20th century.

N A Nielsen skrev:
sg17a, du synger med dit næb, jeg med mit. kfl insisterer på, at hans indlæg er så vigtige, at der må oprettes en ny tråd hver gang, han har noget at sige, så må han også kunne tåle at få at vide, at det han siger ikke giver mening, og at det har han fået at vide før.

sg17a

1. Tidevand har ikke indflydelse på global vandstand. Månen og solen trækker rundt med det samme vand.

2. CU korrigerer for tidevand i sine regionale data.

1) Enig - tidevand er en lavfrekvent (i forhold til bølger og dønninger) støj på vandstand. Den kan med lethed fjernes fra data, da den er periodisk.

respekt for folk som inddrager usikkerhed i betragtningerne. Det er der mange som kunne lære og usikkerhed bør være obligatorisk i al kvantitativ analyse. Det er det desværre ikke.

N A Nielsen skrev:
1. Tidevand har ikke indflydelse på global vandstand. Månen og solen trækker rundt med det samme vand.

kulden-varmen skrev:

N A Nielsen skrev:
1. Tidevand har ikke indflydelse på global vandstand. Månen og solen trækker rundt med det samme vand.

Jo, hvis havbunden bølger op og ned i takt med tidevandet.

Måske man skal se på volumener i stedet for koter, da volumen reelt set må være uden tidevand!

The GMSL rate corrected for GIA represents changes in water mass and density in the oceans. These changes are thought to be predominantly driven by thermal expansion of the oceans and land ice melt (Greenland and Antarctic ice sheets and glaciers).

At any location, the SSH changes over time due to many well understood factors (ocean tides, atmospheric pressure, glacial isostatic adjustment, etc.). By subtracting from the measured SSH an a priori mean sea surface (MSS), such as the CLS01 mean sea surface, and these known time-varying effects, we compute the sea surface height anomalies (SSHA). Each point in the global mean sea level (GMSL) time series plots is the area-weighted mean of all of the sea surface height anomalies measured by the altimeter in a single, 10-day satellite track repeat cycle (time for the satellite to begin repeating the same ground track). Our goal is to observe the changes of the GMSL due to less understood factors, such as ocean mass changes from melting land ice and groundwater depletion, thermal expansion and contraction of the oceans, and the interannual variability caused by phenomena such as the ENSO.

Jeg har ikke kunnet konstatere acceleration af vandstanden ud fra satellit data fra Colerado University. Dette skyldes formodentlig en for kort tidshorisont i sammenhæng med størrelsen af den forventede acceleration og forskellige månecykler dvs. 8.85 og 18.6 års cykleren.

I en diskussion i Ingenøren mellem DMI og GEUS om vandstanden, finder jeg så Baarts artikel. Dette var udgangspunktet.

The observed nodal cycle shows a pattern that is more E–W [east-west, NAN], rather than the equator–poles pattern of the equilibrium. The nodal cycle [18,6 års månecyklus] can thus be safely ignored for global mean sea-level estimates based on satellites

Projection of future sea level change relies on the understanding of present sea-level trend and how it has varied in the past. Here we investigate the global-mean sea level (GMSL) change during 1993–2012 using Empirical Mode Decomposition, in an attempt to distinguish the trend over this period from the interannual variability. It is found that the GMSL rises with the rate of 3.2 ± 0.4 mm/yr during 1993–2003 and started decelerating since 2004 to a rate of 1.8 ± 0.9 mm/yr in 2012. This deceleration is mainly due to the slowdown of ocean thermal expansion in the Pacific during the last decade, as a part of the Pacific decadal-scale variability, while the land-ice melting is accelerating the rise of the global ocean mass-equivalent sea level. Recent rapid recovery of the rising GMSL from its dramatic drop during the 2011 La Niña introduced a large uncertainty in the estimation of the sea level trend, but the decelerated rise of the GMSL appears to be intact.