Vandstanden i verdenshavene

kfl skrev:
Der har på de skeptiske blogs vært en debat om hvorvidt vi har set en acceleration af vandstandsstigninger i verdenshaven.

Boe Carslund-Sørensen skrev:

havtemperaturerne, som slet ikke er påvirkede af UHI.

CBH

Det er noget af en påstand - kan du dokumentere den?

CBH

Jeg venter stadig på din dokumentation!

Det er jo nemt at påstå acceleration i havstigninger når man ikke en gang behøver at kunne se det i data fra virkelighedens data. (who cares??)

Sebastian Mernild har tidligere udgivet et paper, hvori han forudser, at det økologiske og meteorologiske system i Grønland vil nå sit tipping point, og at indlandsisen vil smelte væk i 2040

Det er jo nemt at påstå acceleration i havstigninger når man ikke en gang behøver at kunne se det i data fra virkelighedens data. (who cares??)

Kosmos skrev:

Det er jo nemt at påstå acceleration i havstigninger når man ikke en gang behøver at kunne se det i data fra virkelighedens data. (who cares??)

- tja, heller ikke 'vores egen graf' tyder meget derpå!:



Her er iøvrigt nogle mere detaljerede betragtninger om emnet (fra 2008).

Som det fremgår af disse grafer, er der en del usikkerhed bådei stigningstakten og i accelerationen, men generelt er der en voksende tendens i begge størrelser

Abstract
The coastal zone has changed profoundly during the 20th century and, as a result, society is becoming increasingly vulnerable to the impact of sea-level rise and variability. This demands improved understanding to facilitate appropriate planning to minimise potential losses. With this in mind, the World Climate Research Programme organised a workshop (held in June 2006) to document current understanding and to identify research and observations required to reduce current uncertainties associated with sea-level rise and variability. While sea levels have varied by over 120 m during glacial/interglacial cycles, there has been little net rise over the past several millennia until the 19th century and early 20th century, when geological and tide-gauge data indicate an increase in the rate of sea-level rise. Recent satellite-altimeter data and tide-gauge data have indicated that sea levels are now rising at over 3 mm year−1. The major contributions to 20th and 21st century sea-level rise are thought to be a result of ocean thermal expansion and the melting of glaciers and ice caps. Ice sheets are thought to have been a minor contributor to 20th century sea-level rise, but are potentially the largest contributor in the longer term. Sea levels are currently rising at the upper limit of the projections of the Third Assessment Report of the Intergovernmental Panel on Climate Change (TAR IPCC), and there is increasing concern of potentially large ice-sheet contributions during the 21st century and beyond, particularly if greenhouse gas emissions continue unabated. A suite of ongoing satellite and in situ observational activities need to be sustained and new activities supported. To the extent that we are able to sustain these observations, research programmes utilising the resulting data should be able to significantly improve our understanding and narrow projections of future sea-level rise and variability.

In summary, the estimate of over 1m and higher rise in sea level by 2100 (in next 90 years) seems unrealistic, when analyzed in the context of present sea level rise which is just about 1.5mm to 2.0 mm per year with almost NO component of acceleration. For the global sea level to rise by over 1m in the next 90 years would require acceleration (in sea level rise) of up to 0.28mm/yr2, which is almost two orders of magnitude larger than present. This seems highly unlikely at present given the fact that the earth's climate has not warmed in the last ten years and further that the earth's mean temperature seems to be declining at present.

Jeg glæder mig til at se argumenterne for den omtalte stigning

Her er et enkelt argument:

One important change in these releases is that we are now adding a correction of 0.3 mm/year due to Glacial Isostatic Adjustment (GIA), so you may notice that the rate of sea level rise is now 0.3 mm/year higher than earlier releases. This is a correction to account for the fact that the global ocean basins are getting slightly larger over time as mantle material moves from under the oceans into previously glaciated regions on land. Simply subtract 0.3 mm/year if you prefer to not include the GIA correction

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Kjeld Jul skrev:
Målinger omkr. Storbritannien viser,at vandstanden ikke har været stigende i de sidste 10 år.

http://www.thegwpf.org/uk-sea-levels-increase-10-years/

Conclusions

It is dangerous to draw conclusions about sea level changes from just a ten year sample. Nevertheless, it is abundantly clear that the claimed acceleration in sea level rise has not materialised in UK waters.

Så meget kan verdenshavene stige

AF Kristian Sjøgren, Videnskab.dk


Ny model giver mere præcise beregninger af afsmeltningen fra grønlandske gletsjere.



Hvis al is på Grønland smelter, stiger vandstanden i verdenshavene med godt syv meter. Så galt går det nok ikke, men forskere vil alligevel gerne vide, hvilke faktorer der styrer, hvor meget is der forsvinder fra verdens største ø og dermed også, hvor meget havet kommer til at stige.

For Grønlands ismassetab gælder det, at omkring 50 pct. smelter væk fra overfladen på grund af blandt andet forhøjede temperaturer i luften. De sidste 50 pct. tabt is forsvinder med isbjerge, der brækker af fra øens store gletsjere.