Sea level change

[Evadne]

If you want the definitive answer, see here. It's a new internet-based tool for showing the mean annual sea level, and its trends, on a global scale. You can display it on Google Earth as well.

I had no idea that the inter-annual variation was so, well, variable. It probably explains any recent groundings I may have experienced far more convincingly than "not reading the tide tables properly".

 

[Searush]

OMG! Canada is falling over!

 

[lustyd]

I'm curious how these are measured in order to consider them accurate. Assuming they are relative to land - how can we be sure the land has not moved by 200mm in 30 years? If they were measuring using satelites how could you know that the satelite didn't move by 20cm in 30 years? Seems to be very fine measurements given the time period so if anyone can explain I'd be interested to learn more.

 

[CAPTAIN FANTASTIC]

That explains why I hit bottom so often:

 

[LadyInBed]

I thought sea levels were set to rise with global warming melting the ice caps, from the trends map we seem to have a rise in UK, Europe and the US but a fall in Scandinavia and the Baltic

 

[KenMcCulloch]

I thought sea levels were set to rise with global warming melting the ice caps, from the trends map we seem to have a rise in uk but a fall in Scandinavia and the Baltic

I think Scandinavia is probably still rising gently following the melting of the ice cap after the last ice age. No doubt someone who actually knows about that will be along in due course. I see the Eastern seaboard of the USA is getting its share; it will be interesting to hear the Republican climate change deniers explaining away the flooding of the Washington Mall when that happens, as it surely must.

(Webcraft is away, someone had to say it.)

 

[Evadne]

The fall in scandinavia is due to the uplift of the sea bed ( must learn to type faster). The measurements are from tide gauge readings, which are necessarily attached to the land. Satellite measurements are ground-truthed by "real" measurements like tide gauges. Working out what is actually going on from there is not that simple, as you can imagine. You can take out the long term trend by ticking the box at the foot of the chart on the web site.

 

[2Tizwoz]

I'm curious how these are measured in order to consider them accurate. Assuming they are relative to land - how can we be sure the land has not moved by 200mm in 30 years? If they were measuring using satelites how could you know that the satelite didn't move by 20cm in 30 years? Seems to be very fine measurements given the time period so if anyone can explain I'd be interested to learn more.

Clearly its not easy.

North Shields tide gauge site

The tide gauge building is located on the old fish quay close to the Port of Tyne offices.

The brick tide gauge building contains 2 stilling wells. A Munro IH40 chart recorder is mounted over one of the wells and a wellhead unit over the other. The Munro gauge and the wellhead unit are fitted with precision potentiometers connected to the POL data logger.

The tide gauge is levelled to the tide gauge bench mark supported by Ordnance Survey auxiliary marks.

External users
Sea level pressures and/or elevations from this site are supplied to the following authority:
Port of Tyne Authority

Site history
1974 - A Munro gauge was installed over one of the stilling wells and an Ott digital gauge over the other
1984 - The Ott digital gauge was removed and a wellhead unit was installed
1984 - The DATARING system was installed with potentiometers attached to the Munro gauge and the wellhead unit
1993 - All equipment removed while a new tide gauge building is built
1993 - New building completed and all equipment reinstated
1998 - Wind speed and direction instruments installed
1998 - Both stilling wells blocked. The POL diving team cleared the blockage
2000 - POL data logger installed

Despite these little difficulties in producing an accurate record the Environment Agency has published a chart.

Seemingly the earlier data was collected ten miles upstream near the Swing Bridge in the middle of Newcastle.

The land level which the gauges are mounted on has risen due to earth's crust springing back following the end of the ice age. This produces an additional difficulty requiring an estimation of that effect. what consideration has been given to the demolition of nearby buildings and local water table levels is unclear.

Only in more recent years have the difficulties of satellite accuracy been added to the equation as GPS has been used to calculate and record the relative station height.

 

[Lady Campanula]

Can we blame this on the 'Legacy of the Last Government'....?

And isn't some of it due to bits of Norfolk and Wales falling into the sea. That raises levels - and hackles.

 

[WayneS]

It is rather odd? The last time I opened a bath tap I seem to recall that the water level seemed to equalise across the whole surface.

I am concerend that this whole thing is another scare tactic of the global warming lobby. Islands that are diappearing because of rising sea levels, where sea levels are dropping in other places.

Mybe we all need to look at how humans are causing the tectonic plates to move....

BTW, not directed at the OP or any other party, just my 2p worth

 

[Twister_Ken]

Mybe we all need to look at how humans are causing the tectonic plates to move....

Don't think that can be the case. I tried pushing Europe away from America once, when I was in Iceland. Didn't seem to make any difference.

 

[Habebty]

Parts of Northern Europe and anywhere else that was under the ice sheet during the last ice age are still rising following the thaw and relief from up to a km of ice bearing down on it. I believe this is called isostatic recovery from my O level Geology days! Conversely, land south of the ice sheet is actually sinking (independently of any possible climate change) but if warming of the sea is occurring this will compound the sea level rise in conjuction with isostatic recovery.

This will explain regional variation in sea level change where some places will see a rise and some will see a lowering of sea level..

 

[Evadne]

It is rather odd? The last time I opened a bath tap I seem to recall that the water level seemed to equalise across the whole surface.

I am concerend that this whole thing is another scare tactic of the global warming lobby. Islands that are diappearing because of rising sea levels, where sea levels are dropping in other places.

Mybe we all need to look at how humans are causing the tectonic plates to move....

BTW, not directed at the OP or any other party, just my 2p worth

The first comment is a good point. One thing to remember is that this is a set of tide gauge measurements, i.e. relative to the earth's surface at that point. Some anti warmists point to sea level falls at historical sea level markers as proof of their theories, conveniently forgetting about tectonic uplift in New Zealand and Greece for example, and post glacial rebound further north. The more you look into sea level rises, the knottier the problem becomes. Some early (pro warmist) predictions of huge increases if the poles melt ignored some basic physics, like how much of the ice is floating.

Another other point is that gravity is constant across your bath, but not across the Earth. Large masses like the Greenland ice sheet will attract the water more, and raise sea levels in that vicinity. I've seen reports of some computer models that predict little overall change in sea level in the UK if Greenland melts. Of course all that water will have to go somewhere if it does happen.

This web site isn't there to take a stance in the debate, but to provide some real data rather than supposition and computer modelling. I'm sure that will inconvenience some of the debaters.....

 

[timbartlett]

This web site isn't there to take a stance in the debate, but to provide some real data rather than supposition and computer modelling. I'm sure that will inconvenience some of the debaters.....

Same site, same year, same data, different picture. I wonder why this one isn't the default?

 

[webcraft]

Same site, same year, same data, different picture. I wonder why this one isn't the default?

If you read the front page there is a simple explanation.

- W

 

[timbartlett]

Same site, same year, same data, different picture. I wonder why this one isn't the default?

If you read the front page there is a simple explanation.

- W

Funnily enough, I did read it (that's why I tried looking at the alternative presentation!) And I've just gone back and re-read it. And I still can't see anything that explains why the version I showed isn't the default.

The crux of it is that the version I showed "...results in the loss of stations for which there is not enough data to calculate a trend." i.e. the picture looks better if you remove stations for which the data is inadequate".