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Havniveau stigninger - hvad mener forskningen?


Havniveau stigninger - hvad mener forskningen?04-11-2019 15:50
Peter Villadsen
★★★☆☆
(519)
Det er en kendt sag, at i middel, så stiger havniveauet.
Det er anerkendt, at den gennemsnitlige stigning ligger på omkring 3mm/år lige nu.
Men hvad mener forskningen, at fremtiden vil bringe?
En meget grundig og interessant gennemgang findes her:
https://www.carbonbrief.org/explainer-how-climate-change-is-accelerating-sea-level-rise

I de senere år er mange nye studier kommet frem. Disse studier har en del variation, men samlet set, så forudses en større stigning i havvandsstigningerne end IPCC konservativt tidligere har konkluderet.

"Since the publication of the IPCC report in 2013, we've seen the range of future SLR projections expand significantly, with some studies suggesting the possibility of up to 2.5m of global mean SLR by 2100.

"There are a number of factors driving the uncertainty in future SLR amounts and rates, but the behaviour of the Antarctic and Greenland ice sheets in a warming climate is, perhaps, one of the largest contributors to this uncertainty. In particular, as new studies have come out suggesting the possibility of larger contributions to sea level rise from the Antarctic ice sheet than previously thought, we've seen the upper bound of future SLR projections climb upwards."

Altså: der er stor usikkerhed på, hvordan ismasserne på Grønland og i Antarktis reagerer, men potentielt kan vi allerede i 2100 have temmeligt store vandstandssttigninger.

Even these new estimates may end up being conservative. For example, a recent study by Prof Jonathan Bamber at the University of Bristol and colleagues brought together a group of 22 experts to assess their views of the likelihood of different future SLR scenarios. They found that a global SLR exceeding 2m by 2100 "lies within the 90% uncertainty bounds for a high-emission scenario". This is more than twice the upper value found in the IPCC AR5.


Derudover er der enighed om, at havvandstigningerne accelererer.
There is also evidence of accelerating SLR over the post-1993 period when high-quality satellite altimetry data is available. According to the recent 2018 BAMS State of the Climate report, acceleration in SLR during the post-1993 period is around 0.1mm each year; this means that the rate of SLR is increasing by 1mm per year each decade.

Altså: som det ser ud nu: læg 1 mm til den årlige stigning hvert 10ende år.

Summa: vi ved ikke præcist hvor hurtigt accelerationen i afsmeltningen bliver igennem de næste årtier, men der er en acceleration og en risiko for betragtelige vandstandsstigninger, allerede i år 2100.
04-11-2019 17:31
kfl
★★★★☆
(1843)
Rigtig god henvisning til Carbonbrief.
04-11-2019 20:52
Peter Villadsen
★★★☆☆
(519)
Er satellit målinger af jordens havniveau nu nøjagtigt nok?
Ja, de er faktisk temmeligt præcise. De angiver middel havniveauet med +/-0,4mm/års nøjagtighed. Lige nu angiver NASA, at havniveauet stiger med 3,3 mm/år - det er så +/-0,4mm/år.

Satellite altimetry missions now provide more than 25 years of accurate, continuous and quasi-global measurements of sea level along the reference ground track of TOPEX/Poseidon. These measurements are used by different groups to build the Global Mean Sea Level (GMSL) record, an essential climate change indicator. Estimating a realistic uncertainty in the GMSL record is of crucial importance for climate studies, such as assessing precisely the current rate and acceleration of sea level, analysing the closure of the sea-level budget, understanding the causes of sea-level rise, detecting and attributing the response of sea level to anthropogenic activity, or calculating the Earth's energy imbalance. Previous authors have estimated the uncertainty in the GMSL trend over the period 1993–2014 by thoroughly analysing the error budget of the satellite altimeters and have shown that it amounts to ±0.5 mm yr−1 (90 % confidence level). In this study, we extend our previous results, providing a comprehensive description of the uncertainties in the satellite GMSL record. We analysed 25 years of satellite altimetry data and provided for the first time the error variance–covariance matrix for the GMSL record with a time resolution of 10 days. Three types of errors have been modelled (drifts, biases, noises) and combined together to derive a realistic estimate of the GMSL error variance–covariance matrix. From the latter, we derived a 90 % confidence envelope of the GMSL record on a 10 d basis. Then we used a least squared approach and the error variance–covariance matrix to assess the GMSL trend and acceleration uncertainties over any 5-year time periods and longer in between October 1992 and December 2017. Over 1993–2017, we have found a GMSL trend of 3.35±0.4 mm yr−1 within a 90 % confidence level (CL) and a GMSL acceleration of 0.12±0.07 mm yr−2 (90 % CL). This is in agreement (within error bars) with previous studies. The full GMSL error variance–covariance matrix is freely available online: https://doi.org/10.17882/58344 (Ablain et al., 2018).
04-11-2019 22:49
Peter Villadsen
★★★☆☆
(519)
Måling over tid med vandstands måleudstyr:



De historiske målinger viser som satellit målinger stigende vandstand.
05-11-2019 19:14
Jørgen Petersen
★★★★★
(2036)
At angiv stigningstakten med mange decimaler er ikke udtryk for nøjagtighed. Når man f.eks. regner gennemsnittet af en lang række tal, så får man helt automatisk mange decimaler. Dette fortæller intet om nøjagtigheden i de oprindelige målinger.
07-11-2019 07:42
Peter Villadsen
★★★☆☆
(519)
Jørgen Petersen skrev:
At angiv stigningstakten med mange decimaler er ikke udtryk for nøjagtighed. Når man f.eks. regner gennemsnittet af en lang række tal, så får man helt automatisk mange decimaler. Dette fortæller intet om nøjagtigheden i de oprindelige målinger.


Som fx (5+4+6+1+9)/5 = 5,0000000.
Gennemsnittet af en lang række tal, giver jo rigtigt mange decimaler...
07-11-2019 18:22
Jørgen Petersen
★★★★★
(2036)
Det store spørgsmål er fortsat: Hvordan kan satellitter, som svæver mange hundrede eller mange tusinde kilometer over jorden, måle vandstanden i havene mere præcist en de landbaserede målinger kan?

Tilsvarende er det også et centralt spørgsmål: Bør vi ikke være mere kritisk overfor IPCC og den etablerede klimavidenskab, end vi har været ind til nu?
07-11-2019 23:07
kulden-varmenProfilbillede★★★★★
(2453)
Jørgen Petersen skrev:
Det store spørgsmål er fortsat: Hvordan kan satellitter, som svæver mange hundrede eller mange tusinde kilometer over jorden, måle vandstanden i havene mere præcist en de landbaserede målinger kan?


De måler noget forskelligt. Den nuværende havstigning begyndte omkring år 1700 og vil blive ved i yderligere 500 år hvis klimaet holder. Fordi verdens havenes cyklus er 800 år.

Satellitter kan godt måle ret præcist, hvis de bliver korrigeret rigtigt. Men de måler mest på de store oceaner hvor tyngdekraften er større. Derfor måler de en støre stigning end ved kysterne hvor der en tyk let kontinent-skorpe.
09-11-2019 09:21
Peter Villadsen
★★★☆☆
(519)
Vores børn får det ikke nemt.
Ny forskning viser, at under sidste mellemistid var temperaturen 1 grad højere end idag, mens vandstanden var 10 meter højere.
Afsmeltningen startede i Antarktis og senere fulgte Grønland med.
Stigningen var op til 3 meter pr århundrede.

We examined data from the last interglacial, which occurred 125,000 to 118,000 years ago. Temperatures were up to 1℃ higher than today - similar to those projected for the near future.

Our research reveals that ice melt in the last interglacial period caused global seas to rise about 10 metres above the present level. The ice melted first in Antarctica, then a few thousand years later in Greenland.

Sea levels rose at up to 3 metres per century, far exceeding the roughly 0.3-metre rise observed over the past 150 years.

The early ice loss in Antarctica occurred when the Southern Ocean warmed at the start of the interglacial. This meltwater changed the way Earth's oceans circulated, which caused warming in the northern polar region and triggered ice melt in Greenland.


https://theconversation.com/scientists-looked-at-sea-levels-125-000-years-in-the-past-the-results-are-terrifying-126017?utm_source=facebook&utm_medium=facebookbutton
Redigeret d. 09-11-2019 09:22
09-11-2019 15:06
delphiProfilbillede★★★★★
(5359)
Vores børn får det ikke nemt.
Ny forskning viser, at under sidste mellemistid var temperaturen 1 grad højere end idag, mens vandstanden var 10 meter højere.
Afsmeltningen startede i Antarktis og senere fulgte Grønland med.
Stigningen var op til 3 meter pr århundrede.


Så skal afsmetningen da noget op i gear med en faktor 50 eller 100 Den står jo nærmest stille se side 11 https://www.geocenter.dk/wp-content/uploads/2019/10/Geoviden_3_2019_enkeltsidet.pdf
09-11-2019 17:06
Peter Villadsen
★★★☆☆
(519)
Accelerationen er lige nu 1mm/årti.
Dvs vi ved år 2100 har nået en stigningstakt på 1m/århundrede. Så der skal ikke en faktor 50 eller 100 til, men derimod blot at den nuværende acceleration fortsætter århundredet ud.

Der er dog ingen der ved, hvordan ismasserne reagerer på øget opvarmning af oceanerne - men studierne af tidligere varmeperioder viser, at 3 m/århundrede er muligt.
10-11-2019 05:11
Peter Villadsen
★★★☆☆
(519)

Kilde Zack Labe

Situationen lige nu i Antarktis er, at der er mistet knapt 1 million kvadratmeter af havisen.

https://www.pnas.org/content/116/29/14414

A newly completed 40-y record of satellite observations is used to quantify changes in Antarctic sea ice coverage since the late 1970s. Sea ice spreads over vast areas and has major impacts on the rest of the climate system, reflecting solar radiation and restricting ocean/atmosphere exchanges. The satellite record reveals that a gradual, decades-long overall increase in Antarctic sea ice extents reversed in 2014, with subsequent rates of decrease in 2014–2017 far exceeding the more widely publicized decay rates experienced in the Arctic. The rapid decreases reduced the Antarctic sea ice extents to their lowest values in the 40-y record, both on a yearly average basis (record low in 2017) and on a monthly basis (record low in February 2017).
10-11-2019 09:24
Kosmos
★★★★★
(4931)
...der er mistet knapt 1 million kvadratmeter af havisen

- nå(?) Det lyder da ikke specielt alarmerende!
10-11-2019 10:21
Peder Kruse
☆☆☆☆☆
(25)
Måske ER vi virkelig i en mellemistid
10-11-2019 13:17
Peter Villadsen
★★★☆☆
(519)
Det var 1 million kvadratkilometer
10-11-2019 15:23
delphiProfilbillede★★★★★
(5359)
@Peter er du i det heletaget klar over hvor lidt energi der skal til at optø 1 mio. km2 is hvis det antages isen igennemsnit er 2 m. et det et samlet volumen på 2000 Km3 som altså er smeltet over flere årtier.

Se iøvrigt https://www.geocenter.dk/wp-content/uploads/2019/10/Geoviden_3_2019_enkeltsidet.pdf
10-11-2019 17:05
Peter Villadsen
★★★☆☆
(519)
Smeltevarmen for is er 334 kJ/kg.
10-11-2019 21:42
delphiProfilbillede★★★★★
(5359)
Smeltevarmen for is er 334 kJ/kg.


Eller 80 kcal/kg som bevirker at der skal 0,1 MWh til at smelte 1 ton is.

Hvis vi antager at massen af havis er reduceret med f.eks. 200 Km3 årligt så kræver det 20.000 TWh energi at tø isen. Eller en konstant effekt på 2,2 TW som omregnet kræver en ekstra backradiation fra drivhuseffekten med 0,0044 w/M2.

Bla. en af mange forhold som siger alt om at menneskeskabt drivhuseffekt er aldeles harmløs.
Redigeret d. 10-11-2019 21:44
10-11-2019 23:06
Peter Villadsen
★★★☆☆
(519)
Delphi, vi kan alle lege med lommeregneren, men du er ikke et orakel med dine forhastede og overilede konklusioner.

Tidligere udregnede du at oceanerne ikke opvarmedes noget særligt ved at beregne en gennemsnitstemperatur for oceanerne beregnet på den samlede vandmængde.
Du glemte blot, at 60 % af energien afsættes i overfladen.

Lyt nu for en gangs skyld til forskningen, der ikke opererer udfra simple skøn eller overfladiske betragtninger, men faktisk forsøger at frembringe brugbare analyser.

Though warming has not been uniform across the planet, the upward trend in the globally averaged temperature shows that more areas are warming than cooling. According to the NOAA 2018 Global Climate Summary, the combined land and ocean temperature has increased at an average rate of 0.07°C (0.13°F) per decade since 1880; however, the average rate of increase since 1981 (0.17°C / 0.31°F) is more than twice as great.

The 10 warmest years on record have all occurred since 1998, and 9 of the 10 have occurred since 2005. The year 1998 is the only year from the twentieth century still among the ten warmest years on record. Looking back to 1988, a pattern emerges: except for 2011, as each new year is added to the historical record, it becomes one of the top 10 warmest on record at that time, but it is ultimately replaced as the "top ten" window shifts forward in time.

By 2020, models project that global surface temperature will be more than 0.5°C (0.9°F) warmer than the 1986-2005 average, regardless of which carbon dioxide emissions pathway the world follows. This similarity in temperatures regardless of total emissions is a short-term phenomenon: it reflects the tremendous inertia of Earth's vast oceans. The high heat capacity of water means that ocean temperature doesn't react instantly to the increased heat being trapped by greenhouse gases. By 2030, however, the heating imbalance caused by greenhouse gases begins to overcome the oceans' thermal inertia, and projected temperature pathways begin to diverge, with unchecked carbon dioxide emissions likely leading to several additional degrees of warming by the end of the century.



Klimaændringerne er igang, enhver kan se det, og på sigt vil menneskehedens problemer øges i takt med højere temperaturer blandt andet baseret på, at vi ikke har bygget vores byer, så de er robuste overfor stigende vandstand.
Dertil kommer så skader forårsaget af øget ekstreme hedebølger, øget tørke, øget skovbrande, øget ekstremnedbør mm.

Lyt til forskningen. Det er det eneste sted, der er seriøs viden at finde.
14-11-2019 14:10
delphiProfilbillede★★★★★
(5359)
Du glemte blot, at 60 % af energien afsættes i overfladen.




Ca 40 % af den energien som fanges i jordens klimasystemer ender i Oceanernes 300 m øverste vandmasser, og netop her er der fanget 120 zetta joule energi siden 1970. Det er en gennemsnitlig opvarmning på 0,005 grad hvert år af de 300 m øverst i oceanerne.

De antagelser og udmeldinger forskningen kommer med er jo grundløse og lad dog være med at lytte til det bras.
Redigeret d. 14-11-2019 14:12
14-11-2019 17:49
Jesper-Midtfyn
★★☆☆☆
(213)
Ved ikke hvordan du er nået frem til dine tal.

Men hvis vi tager fat i forskellige undersøgelser, er der tydeligvis en større stigning i havtemperaturerne på forskellige havdybder, hvilket giver grund til bekymring.

Denne undersøgelse tager eksempelvis fat i temperaturer på mellem 3 og 63 meters dybde i Den Mexicanske Golf.

Af abstractet fremgår:

We quantified trends in the 1985 to 2015 summer bottom-water temperature on the northern Gulf of Mexico (nGOM) continental shelf for data collected at 88 stations with depths ranging from 3 to 63 m.

The analysis was supplemented with monthly data collected from 1963 to 1965 in the same area. The seasonal summer peak in average bottom-water temperature varied concurrently with air temperature, but with a 2- to 5-month lag.

The summer bottom-water temperature declined gradually with depth from 30 C at stations closest to the shore, to 20 C at the offshore edge of the study area, and increased an average 0.051 C y-1 between1963 and 2015.

The bottom-water warming in summer for all stations was 1.9 times faster compared to the rise in local summer air temperatures, and 6.4 times faster than the concurrent increase in annual global ocean sea surface temperatures.

The annual rise in average summer bottom-water temperatures on the subtropical nGOM continental shelf is comparable to the few published temperature trend estimates from colder environments.

These recent changes in the heat storage on the nGOM continental shelf will affect oxygen and carbon cycling, spatial distribution of fish and shrimp, and overall species diversity.


Link til artiklen Trends in summer bottom-water temperatures on the northern Gulf of Mexico continental shelf from 1985 to 2015

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0184350
Tilknyttet billede:

15-11-2019 07:19
Peter Villadsen
★★★☆☆
(519)
Påstand: Det er en gennemsnitlig opvarmning på 0,005 grad hvert år af de 300 m øverst i oceanerne.



The current paper analyses the recent trends of Red Sea surface temperature (SST) using 0.25° daily gridded Optimum Interpolation Sea Surface Temperature (OISST) data from 1982 to 2016. The results of 3 different GFDL (Geophysical Fluid Dynamics Laboratory) model simulations are used to project the sea surface temperature (hereafter called Tos) under the four representative concentration pathway scenarios through 2100.

The current research indicates that the spatially annual mean (from 1982 to 2016) Red Sea surface temperature is 27.88 ± 2.14°C, with a significant warming trend of 0.029°C yr−1. The annual SST variability during the spring/autumn seasons is two times higher than during the winter/summer seasons. The Red Sea surface temperature is correlated with 13 different studied parameters, the most dominant of which are mean sea level pressure, air temperature at 2 m above sea level, cross-coast wind stress, sensible heat flux, and Indian Summer Monsoon Index.

For the Red Sea, the GFDL-CM3 simulation was found to produce the most accurate current SST among the studied simulations and was then used to project future scenarios. Analysis of GFDL-CM3 results showed that Tos in the Red Sea will experience significant warming trends with an uncertainty ranging from 0.6°C century−1 to 3.2°C century−1 according to the scenario used and the seasonal variation.


https://www.sciencedirect.com/science/article/pii/S0078323419300442

For det Røde hav altså omtrentligt anslået 2 grad stigning i overfladetemperaturen pr århundrede.
Det er så forventet 0,02 grad pr år, lige nu er opvarmningen målt til 0,029 grad pr år.
Redigeret d. 15-11-2019 07:54
16-11-2019 16:31
Jesper-Midtfyn
★★☆☆☆
(213)
Der er en noget lavere hastighed for opvarmning af oceanerne, jo dybere vi kommer ned i havet, ifølge en forskergruppe anført af professor Dean Roemmich. I artiklen Unabated planetary warming and its ocean structure since 2006 i Nature Climate Change skriver de følgende.

The net 0–500 m global average temperature warmed by 0.005 °C yr−1. Between 500 and 2,000 m steadier warming averaged 0.002 °C yr−1 with a broad intermediate-depth maximum between 700 and 1,400 m.


En meget markant udvikling tættere på havoverfladen, som de to nævnte artikler artikler i de foregående indlæg illustrerer og en knap så markant udvikling på større havdybder.




Deltag aktivt i debatten Havniveau stigninger - hvad mener forskningen?:

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