[alancalverd (OP)]

I heard a radio program last night on how rising sea levels due to global warming had drowned significant areas of he Solomon Islands. Shock, horror, doom, loss of traditional and indigenous etcetera. No figures were given but there was a strong implication that the mean sea level had risen at least 60 cm in 50 years.

Now AFAIK all the oceans are connected, and water flows. So if the South Pacific has risen by two feet in a lifetime, so has the Mediterranean (much easier to measure as it is almost tideless). Has it? I think not.

There was just one tiny hint of a flaw in the strongly implied Global Warming is Killing Everything hypothesis. The reporter  mentioned that the Solomons are volcanic islands. Yep, right on the Pacific ridge. Here today and gone (geologically speaking) tomorrow.   

[Tim the Plumber]

Oh, yes.

Never put into the mix anything other than Global warming or the message will be lost. Rember we are all doomed!

[evan_au]

The patterns of sea level change involve many local factors:
- Apparently, Scotland is rising out of the sea, as it rebounds from its heavy load of ice in the last ice age. The land is rising faster than the sea level is rising. Unfortunately for southerners, the UK is tipping as a block, which means that sea level on the Thames is rising faster than the ocean is rising.
- I heard a recent interview with some archaeologists studying an island off the Canadian coast as a potential stopping point for humans entering North America via the Bering Straight. They were interested in this island because it was on the balance point between sea level rise from melting glaciers and the gravitational attraction of large masses of ice on land. So it had been surrounded by water without being flooded during and since the last ice age. 
- Fortunately, satellites are now able to obtain global measurements, free from these local anomalies
- The current global estimate is 2-3 mm/year.
- The factor that will affect people in the most dramatic way is storm surges. With a tidal range of over 1m in many oceans, a couple of millimeters change in the average is not noticeable. However, during a storm, considerable water is driven inland, and a small change in height makes a big difference to the amount of damage.
See: https://en.wikipedia.org/wiki/Sea_level_rise

[Tim the Plumber]

Do you think that the storm surge amount will alter over the coming century?

[chris]

There is one thing to consider - and I regret that I cannot locate the reference this precise second - but the huge mass of ice aggregated over Antarctica, which is not floating and hence not displacing any water - exerts a considerable gravitational effect on surrounding seawater, meaning that there is a circumpolar water bulge; if the ice melts then that water redistributes, causing a greater rise in sea level than just the ice melting alone.

[Bored chemist]

We can't do a lot about the height of the Solomon Islands. (A fairly cheap GPS system would answer that actual question you pose but I presume that you don't really care about that, since you seem to be seeking to make some sort of rhetorical point)

But we can stop making things worse for them by not raising global temperatures and thereby melting the antarctic ice.
So, lets try and focus on that.

[SeanB]

The problem is there is no real reference datum. Satellite measurements show something, but even there an average will give you just that, an average. Not going to say all is rising, just that some parts are changing relative to others, which is really all they can show.  All you can say for sure is that ice caps in some areas are retreating, some might be growing, and that the climate is changing, with a contribution from man made CO2, and also a much bigger change from the water vapour in the air.

Pretty much all the satellite data shows is that Everest is growing above the local sea level by a few centimetres a year, and that weathering of the rock is not as much, so it keeps on growing.

[Bored chemist]

The problem is there is no real reference datum.

Satellites let you use the centre of gravity of the Earth as a datum.
From our point of view, that's going nowhere.

[SeanB]

Centre yes, but that is also going to change as a result of motion of the rock in the core. The orbit of the satellites will change as a result, and thus the height data is not going to be an exact reproducible measurement. All the measurements will be relative, just choose a reference datum for it.

[Bored chemist]

Centre yes, but that is also going to change as a result of motion of the rock in the core. The orbit of the satellites will change as a result, and thus the height data is not going to be an exact reproducible measurement. All the measurements will be relative, just choose a reference datum for it.

You do know that the centre of gravity of the Earth can't move unless we get hit by something external, don't you?
The land can't go down everywhere simultaneously. So the average of "where all the rock is" stays in the same place.
The point is that you can measure the height of, for example, the Solomon Islands from that CoG and the water finds its own level wrt that same CoG.
We also know where the Satellites orbits are WRT each other so we can use their effective CoG as a reference. There's nothing out there to move them so they will provide a very stable reference framework too.

[puppypower]

If you look at the earth, its gravitational field is not symmetrical. It is actually asymmetrical. The asymmetry allows the ocean to rise in some places and sink on other places. Below is a representation of the earth as a function of surface gravity.

[Bored chemist]

If you look at the earth, its gravitational field is not symmetrical. It is actually asymmetrical. The asymmetry allows the ocean to rise in some places and sink on other places. Below is a representation of the earth as a function of surface gravity.

So?
It's very pretty, but it shows that the field is almost constant (within about 50ppm).
The GPS satellites are high enough to see the average of all that (Don't forget that they are attracted by the gravity from stuff on the "far side" of the earth too.)

[alancalverd (OP)]

But surely the asymmetry won't have changed much in 50 years? If it has, then Some of Us Are Doomed.

[PhysBang]

I heard a radio program last night on how rising sea levels due to global warming had drowned significant areas of he Solomon Islands. Shock, horror, doom, loss of traditional and indigenous etcetera. No figures were given but there was a strong implication that the mean sea level had risen at least 60 cm in 50 years.

Now AFAIK all the oceans are connected, and water flows. So if the South Pacific has risen by two feet in a lifetime, so has the Mediterranean (much easier to measure as it is almost tideless). Has it? I think not.

There was just one tiny hint of a flaw in the strongly implied Global Warming is Killing Everything hypothesis. The reporter  mentioned that the Solomons are volcanic islands. Yep, right on the Pacific ridge. Here today and gone (geologically speaking) tomorrow.   

Yeah. I'm not surprised that a global warming denier is coming here with some supposedly vaguely remembered program (not named, no citation whatsoever) that supposedly delivers a straw man argument against global warming.

This, and the repeated anti-Catholic bigotry, really reflect well on the moderation here and on the naked scientists in general.

[alancalverd (OP)]

We can't do a lot about the height of the Solomon Islands. (A fairly cheap GPS system would answer that actual question you pose but I presume that you don't really care about that, since you seem to be seeking to make some sort of rhetorical point)

But we can stop making things worse for them by not raising global temperatures and thereby melting the antarctic ice.
So, lets try and focus on that.

Plenty could indeed be done about the Solomon Islands if anyone thought the matter sufficiently important, and the problem was indeed due to climate change  -  vast areas of Holland were directly claimed from the sea and a substantial part of East Anglia would be under water if our ancestors hadn't built dams and pumps. 
 
I care about honest reporting, and the effect of simplistic or dishonest reporting on human motivation. Since climate change is inevitable, wrongly blaming any inconvenience on climate change is demoralising, demotivating, and playing into the hands of politicians and pseudoscientists who make their living from telling you it's all your fault. 

Humanity can probably cope with a few millimeters of sea level rise per year until the next ice age, but I don't see any practical means of preventing volcanic islands from disappearing almost as fast as they appear.

One might have hoped for better from Radio 4  ("Costing the Earth" BBC R4, 2100BST, 19/4/17).   

[Bored chemist]

Plenty could indeed be done about the Solomon Islands
...
but I don't see any practical means of preventing volcanic islands from disappearing almost as fast as they appear.

Feel free to make up your mind.

[evan_au]

the height data is not going to be an exact reproducible measurement

All scientific experiments have some experimental error - the challenge is to design your experiment so that the experimental error is much less than the thing you are trying to measure - in this case, a change in sea surface level of a couple of millimeters per year, superimposed on a daily (or twice-daily) tidal swing of a meter or more, and variation of a meter or more every few seconds from waves.

In the case of the GPS satellites, there is continual measurement, calibration and correction, with several carefully-surveyed monitoring sites around the world.

But sea-level is best monitored by radar reflections from the sea surface., eg See: https://en.wikipedia.org/wiki/Ocean_Surface_Topography_Mission

It seems that President Trump has his own plan to prevent sea-level rise: remove funding from any project that is attempting to measure it.

[Tim the Plumber]

There is one thing to consider - and I regret that I cannot locate the reference this precise second - but the huge mass of ice aggregated over Antarctica, which is not floating and hence not displacing any water - exerts a considerable gravitational effect on surrounding seawater, meaning that there is a circumpolar water bulge; if the ice melts then that water redistributes, causing a greater rise in sea level than just the ice melting alone.

Do you think that this is at all possible within the next 5,000 years given the very low temperatures of Antarctica?

[Tim the Plumber]

We can't do a lot about the height of the Solomon Islands. (A fairly cheap GPS system would answer that actual question you pose but I presume that you don't really care about that, since you seem to be seeking to make some sort of rhetorical point)

But we can stop making things worse for them by not raising global temperatures and thereby melting the antarctic ice.
So, lets try and focus on that.

Again, do you really think that Antarctic ice is at all in danger of melting?

[jeffreyH]

https://www.nasa.gov/content/goddard/antarctic-sea-ice-reaches-new-record-maximum
The editor's note should be read first. This article indicates the variety of changes that can be expected in a chaotic system. The fact that it is chaotic means unexpected things will happen. It is not easy to plan for the unexpected. Since it could be a positive or negative change from our viewpoint.