Sea Levels Around Tonga Up 10 Centimeters In 13 Years

The sea level around Tonga appears to have risen by about 10 centimetres in the past 13 years, according to the latest data from the South Pacific Sea Level and Climate Monitoring Project.

Our reporter, Sean Dorney, says the Australian-funded project has been in operation since late 1992, and each month the latest figures from the 12 monitoring stations around the Pacific are published. The latest Monthly Data Report - for December - shows that for the stations that have been monitored for more than 10 years, the sea level rise trend is highest in Tonga with a rise of 8.4 millimetres a year.

The sea level is rising at every station, but there are wide variations. The Cook Islands station is showing a rising trend less than one eighth of that in Tonga. At Tuvalu, which will be experiencing its highest tides in 15 years next week, the trend in sea level rise over the past 13 years has been 5.7 millimetres a year, a cumulative rise of about seven centimetres.

The project coordinators urge that caution be exercised in interpreting any of the trend data because they say longer term recordings are needed.

EDIT

http://abcasiapacific.com/news/stories/asiapacific_stories_1575144.htm

Problem is that we MEASURE altitude from Average Sea Level. By definition, it is zero. If it appears that Average Sea Level has risen or fallen, how can we be certain that the LAND our guage is attached to has no risen or fallen? (It does! The Scandinavian counties are still rising due to the weight that was removed from them when the last glaciers melted. Likewise, much of Canada is rising.

Also Average Sea Level can be hard to ascertain. Winds change sea level. Tides change sea level. A systematic change in an offshore current can change it too.

And the sea is not flat at all, even if you could miraculously remove all waves, there are large peaks and valleys in the ocean's surface, some related to temperature, pressure and currents, some related to mass concentrations in the Earth.

or even if the idea I'd like to hear your thoughts on this idea.

Intuitively of course, many of us know the sea is rising, simply by going to the beaches where we went as children. Most of them are much narrower.

However, in order to quantify the matter, how would laser interferometry work? Sea level would in any instant change owing to wind, tide etc. However if one were to take repeated measurements at particular points on the surface of the sea, one could, in theory, develop a very good understanding of the average values at particular points on the surface of the earth. If one were to develop a set of such measurements at different points via satellite, one could determine at least a general trend and its size, especially if one corrected for known fluctuations like tides or high intensity storms.

There are portions of the earth where the sea is relatively calm for long periods. These suggest good sampling points.

Here's another idea. It is known that the earth's rotation has slowed slightly owing to the increase in dams at high altitude, which has changed the moment of inertia of the planet as a hole, thus slowing the day. Perhaps we could look for changes in the other direction. As the glaciers melt, more water is contained in the oceans. Therefore the moment of inertia is decreased and the earth speeds up.

The nuclear tests of the early 1960's labeled most of the surface of the planet with radioisotopes. Some testing sites have probably been seldom disturbed and many are on small Islands. Some of these isotopes are insoluble and almost certainly coated the sea floor. Perhaps some data exists about the intensity of radiation on the surface of the water shortly after a test. One could, in theory go into the Bikini lagoon and measure the time corrected attenuation of the radiation by seawater. If one also corrected for debris fields, you might be able to glean some data.

Ideas. Maybe crazy ideas. But I wonder about this question.

And that number does rise.

Also we get good numbers from radar sats, but those are hard to interpret because there is too much information!

Your idea of measuring the rotation changes has some merit, but this is also a noisy data set as things like solar wind and tectonics effect it. Still if you watched it long enough you could likely confirm the data from the guages.

I would count beach erosion as a more visible factor than sea level rise. For now.

Erosion has been an eternal process. It is difficult to imagine that beaches existed in the 1950's that were immune to erosion.

In some cases, silt flows have been cut off by dams and by dredging and wetland depletion, but I'm pretty well convinced that is not the whole story.

Erosion would be a major factor, if the influx of sand had been stopped by a seawall up the coast. A lot of beaches rely on a regular flow of incoming material to maintain thier profiles - cut this off and the thing dissapears.

If it's beach that doesn't rely on this, or the upstream coast has not been re-enforced, then you could point at sea-level changes as a suspect.

Tidal gagues are the most effective way of measuring the change for the moment, though.

is that like 4"? I'm not really good at converting between them. TIA.

...approximately.

If you round to 25 you save yourself lots of problems in mental conversion.

:P

Okay, I admit it. I used a calculator.

It's the damnedest thing. I've used metric tools and rulers enough to have a fair visual sense of how large something is in metric units (I'm fairly accurate at judging the difference between 9mm and 10mm bolts by sight, for example). And like most Americans, I can also estimate a short distance in Imperial units. But for some reason, it seems like I've stored those two 'skills' in completely different parts of my brain.

For example, what I tend to do, when asked by my wife 'about how many inches is 8 centimeters?', is I'll hold my fingers apart about what I think is 8 centimeters, then LOOK at my fingers, and estimate how big that is in inches ("it's about three inches"). For some reason, I can't skip the step where I use my fingers to estimate the distance and do it all in my head. I'm thinking I developed those skills in my visual cortex somewhere instead of in my 'main brain', if such distinctions can be made.

In the end, if she needs it to be accurate, I use a calculator...:)

However, this is all off topic.

Back to our regularly scheduled Earth Doom Watch...

But I'd never admit to it on the internet. You're a brave man, and knowing what to do with it helps.
:evilgrin:

I mean...she asks me how big 23 centimeters is! Yeah, that's it!

:rofl: