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Author Topic: Quick, Where's the Drain Plug?  (Read 2984 times)

Offline CliffordK

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Quick, Where's the Drain Plug?
« on: 25/07/2011 10:16:17 »
According to the Aviso website, this year has seen between cm and 1cm drop in global sea levels.

http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/


The University of Colorado also seems to have a similar drop, although they indicate that it may be leveling out some.
http://sealevel.colorado.edu/

The average increase in sea level that we have seen over the last few years has to do with a combination of glacier ice loss around the globe, and warming in the oceans which in turn causes thermal expansion.

Late 2010 and early 2011 has either brought significant cooling of the oceans, or more snow and ice deposition in glaciers around the world.


 

Offline yor_on

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« Reply #1 on: 26/07/2011 10:08:13 »
I don't know Clifford. This is science 'on the raise' sort of, comparatively new and uncertain, the computer models constantly changing with better information. You have the tectonic raise of plates for example

"Because the land surfaces are dynamic, with some locations rising (e.g., Hudson Bay due to GIA) or sinking (e.g., New Orleans due to subsidence), relative sea level changes are different across world coasts. To understand the relative sea level effects of global oceanic volume changes (as estimated by the GMSL) at a specific location, issues such as GIA, tectonic uplift, and self attraction and loading (SAL, e.g., Tamisiea et al., 2010), must also be considered. We do calibrate the altimeter sea level measurements against a network tide gauges to discover and monitor drift in the satellite (and sometimes tide gauge) measurements."

And.

"The term "global mean sea level" (GMSL) in the context of our research is the eustatic sea level. The eustatic sea level represents the level if all of the water in the oceans were contained in a single basin. Changes to this eustatic level are caused by changes in total ocean water mass (e.g., ice sheet runoff), changes in the size of the ocean basin (e.g., GIA), or density changes of the water (e.g., thermal expansion). A single GMSL estimate is made by computing the area-weighted mean of all the satellite SSH measurements every 10 days (time to repeat the satellite track; also known as a "cycle"). The time series of the GMSL estimates over the TOPEX and Jason missions beginning in 1992 to the present indicates a mostly linear trend after correction for inter-mission biases between instruments. The GMSL rate corrected for GIA represents changes in water mass and density in the oceans. These changes are thought to be predominantly driven by thermal expansion of the oceans and land ice melt (Greenland and Antarctic ice sheets and glaciers)."

Here's a FAQ. 

I know one thing though. We need more satellites up there.
 

Offline Don_1

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Quick, Where's the Drain Plug?
« Reply #2 on: 26/07/2011 12:00:28 »
I don't think I would take a change in sea levels of the magnitude of - 1cm in one or two years as any sort of indicator. Thermal expansion and contraction, snow and ice levels on covered land masses and even the volume of evaporated water in the atmosphere, among other conditions, need to be taken into account. It is more the level of the oceans spread over a longer time frame and with all those variants taken into account which we should take notice of.

What's more, sea levels are not the only indicator we should take into account when looking at our climate. If this lowering of sea levels is an indicator of global cooling, how do you explain the fact that here in the UK, our apple crops are ready for picking a full month earlier than the usual harvest time of September? Our early crop strawberries were similarly ready to harvest a month early and roses bloomed early.

Conversely, I have a Hibiscus which would normally be in full flower by now, and pretty picture it makes. Yet it has only opened about two dozen flowers so far this year. The rest of the buds have remained tightly closed. In actual fact, only this week have the buds begun to swell and are showing signs of opening.

I think it is wrong to base climate change on the evaluation of any one ecological system, we need to put the whole picture together to come to some meaningful conclusion.

The above said, my personal feeling is that you can't make an omelette without breaking some eggs. Of course we are having an effect on the climate, the question is to what extent? But whatever that extent may be, I hardly think it not worth while to try to limit our effect on our climate and atmosphere. In a few years, or hundred years, we can always say 'we needn't have bothered', but will we be around to say 'we should have taken the trouble.'?
« Last Edit: 26/07/2011 12:03:32 by Don_1 »
 

Offline CliffordK

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Quick, Where's the Drain Plug?
« Reply #3 on: 27/07/2011 09:16:51 »
I do believe the recent drop in global sea levels is likely real, and due in part to the La Nia ocean currents, and generally cooler sea surface temperatures this year.  But, the slow rise of sea levels will likely resume at some point in the future.

I can't tell how much of an adjustment is made for tide gauges, but I would hope the satellites could be run independently from the tide gauges as the goal should be to create an independent assessment of the sea level.

According to the University of Colorado, they also add 0.3mm per year (about 10% of their estimated rise) due to glacial isostatic adjustment (GIA).  This is not due to any measured rise, but is rather a purely calculated volume change in the oceans that they are representing as a sea level increase.

Actually, I would rather see the sea level calibrated based on satellite measured elevations of fixed structures such as buildings.

Anyway, the recent trend appears to be more than some previous cooling periods, but if the cooling isn't long-term, then the reprieve from sea rise won't either.
 

Offline yor_on

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« Reply #4 on: 28/07/2011 11:30:59 »
Yeah, it's something of a conundrum isn't it?

We desperately need more data to define what's happening, at the same time that some of that new data gives us information that we still don't make a perfect sense of :) But I think that without that data we would have to turn to that old man with his old briar, and one-eyed parrot. "Sir, will it rain?" I prefer real live satellite data myself, although, I wouldn't mind him getting involved in interpreting it though :) After all, one never knows.
 

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Quick, Where's the Drain Plug?
« Reply #4 on: 28/07/2011 11:30:59 »

 

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