sea level rise - measured how, exactly?

Citizen Runner wrote:

the shill wrote:

And of course forecasting is LESS difficult than hindcasting because one is less constrained by not knowing the unknowns...

Sorry, cheap shot I know, couldn't resist. :-)

Forward projections are made with an explicitly specified set of assumptions which may or may not be actualized and with error margins increasing with time. Flawed as the process may be the alternative is uninformed and perhaps wishful thinking.

You know, the two of you should probably just exchange email addresses. Every one of these shill-started threads sounds like exactly same dialogue between the two of you and ends when CR gets tired of it.

Seriously, exchange emails and be done with it.

UNO wrote:Every one of these shill-started threads sounds like exactly same dialogue between the two of you and ends when CR gets tired of it.

Seriously, exchange emails and be done with it.

I think I've only ever started this thread on a climate-related topic, although I can't be 100% sure. I've chimed in on many of these, although not in a few months I don't think. I did flip CR an email address last year but he/she didn't bite. CR has been a source of a lot of great information in these threads.

the shill wrote:

That's not really correct. The plot of sea level change I provided earlier was smoothed. Here are a couple of example US tide gauges with trends also plotted:

Image:

http://i57.tinypic.com/14c7mf9.jpg

There is quite a lot of short term variability. There is not very significant decadal variability from the overall trend, mind you. I find that a little puzzling frankly. In the 1970s, when global temperatures were in a lengthly slight decline, and there was local readvance of mountain glaciers, one might expect sea level to drop for both steric and water balance reasons, but it did not.

Yeah, I missed that mean sea level was not only spatially averaged, but also temporally smoothed. Still, the causes of the short term variability are probably more driven by winds and currents while the changes in temperatures in the ocean are much more buffered than air temperatures. I am guessing that the same holds for glacial melting, too.

As far as the seventies went, you need to be careful about assuming that just because the average air temperature declined that the sea heat content declined. The "pause" in warming over the last decade has been driven by large amounts of heat being absorbed into the near surface depths of the ocean. I can't remember what the cause of the decline in temperatures during the 70s was, but there might not have been such a dramatic decline in ocean temperatures as air temperatures and that could be a reason why you don't see a decline in sea levels.

the shill wrote:

Bad Wigins wrote:the steadily melting ice is a good basis.

Not looking for facile responses. Can't prevent them either I suppose...

They're what you're asking for, so why would you want to prevent them?

Anyone responding to you seriously is a fool.

dingle wrote:... the causes of the short term variability are probably more driven by winds and currents while the changes in temperatures in the ocean are much more buffered than air temperatures. I am guessing that the same holds for glacial melting, too.

As far as the seventies went, you need to be careful about assuming that just because the average air temperature declined that the sea heat content declined. The "pause" in warming over the last decade has been driven by large amounts of heat being absorbed into the near surface depths of the ocean. I can't remember what the cause of the decline in temperatures during the 70s was, but there might not have been such a dramatic decline in ocean temperatures as air temperatures and that could be a reason why you don't see a decline in sea levels.

Well, OK, but I think the idea that the ocean is "hiding" the missing heat is an interesting theory but needs to be tested with actual data. Perhaps CR can share some. Anyhow, the global sea SURFACE temperatures show the same trend as global air temperatures:

And here is the sea surface temperature overlain on the sea level trend:

Oft times a ruler is used as a measuring device. For large increases a yardstick may be required.

Bad Wigins wrote:They're what you're asking for, so why would you want to prevent them?

Well, I'll admit I enjoy some of the off-topic stuff, even the insults, but generally only when they are somewhat witty or at least reflect average intelligence. :-)

Citizen Runner wrote:Forward projections are made with an explicitly specified set of assumptions which may or may not be actualized and with error margins increasing with time.

Or as Neils Bohr is reputed to have said, "Prediction is very difficult, especially about the future" :-)

You've been posting sea level rise graphs which haven't slowed recently (probably the opposite). By itself that's a reasonable proxy for the ocean absorbing heat at essentially a constant rate.

That said, there we have direct measurements of ocean heat content change as a corroborating line of evidence:

HadCRUT4 = 1/3 * CRUTEM4 + 2/3 * HadSST3 by definition, that is 2/3 of the global surface air temperature you've plotted is the sea surface temperature you've plotted. It would be pretty remarkable if the two weren't highly correlated.

These wouldn't be expected to match as explained previously.

Citizen Runner wrote:HadCRUT4 = 1/3 * CRUTEM4 + 2/3 * HadSST3 by definition, that is 2/3 of the global surface air temperature you've plotted is the sea surface temperature you've plotted.

Can you cite a link? I'm hunting and can't find this anywhere. I don't doubt you, just applying the philosophy "trust, but verify" :-)

OK I managed to answer my own dumb question. The HADCRUT4 global anomaly is a combination of the spatially averaged grid values from the CRUTEM4 and HADSST3, which isn't precisely 2/3 sea and 1/3 land temperature anomaly but close enough for message board discussions.

Here are plots of the land and sea trends (top) and global trend (bottom) for comparison:

Here is the ocean heat content plot you linked, compared with the sea level trend:

I've scaled them vertically to give a similar overall trend. I don't see much shorter term similarity, based on a naive "gut" review, but others may.

For interest (if perhaps just my own), here is the sea surface temperature anomaly (SST3) compared to the ocean heat content trend:

the shill wrote:I don't see much shorter term similarity, based on a naive "gut" review, but others may.

I wonder, though, if some kind of superposition of the ocean heat content and ocean surface temperature plots might give a better correlation with the inferred sea level trend? I suppose it ought to. Maybe the very first link you cited answers that question...? Alas I'd better do some paid work today and leave this be

Good catch, the 1/3 + 2/3 I was thinking of is the combination of the Southern and Northern Hemisphere land surface anomaly, not the land + sea. Regardless, the point remains that the global anomaly is in large part the SST anomaly.

I doubt it. Ocean heat content anomaly is the cumulative sum of energy flux in/out of the ocean. Surface temperature is one of the factors, but it is not a simple relationship and there are no direct global measurements of ocean surface flux. What has been done is to work the reverse problem, that is, use ocean heat content data to infer net flux. e.g.

Citizen Runner wrote:I doubt it.

How come?

My naive expectation is that if global sea level is largely influenced by ocean temperature (driving steric change) and changes in glacier volume (which should follow global temperature in some fashion), then combining ocean heat content in some way with global temperatures (not just sea surface temperatures I suppose) ought to produce something with a stronger correlation with sea level trend.

From a naive comparison I'd suggest the correlation does get a bit better (than for just temperature or ocean heat content) but there is still unexplained variability.

Anyway, now I'm just navel-gazing, idly speculating and wondering to no obvious purpose or benefit other than curiosity. I don't think there's any question sea level is "rising" globally, or that it is linked with "global warming" to some strong degree. I continue to wonder about the significance of rising sea levels, and the bit of scientist in me wonders about how confident we can be in its "measurement."

the shill wrote:

Citizen Runner wrote:I doubt it.

How come?

Theoretically:

- Page 3: "Major Heat Budget Terms at the

Sea Surface" and following

or empirically:

Citizen Runner wrote:Theoretically:

http://www.geo.cornell.edu/ocean/p_ocean/ppt_notes/4_HeatFlux.pdf

- Page 3: "Major Heat Budget Terms at the

Sea Surface" and following

or empirically:

http://www.cgd.ucar.edu/staff/cdeser/docs/park.sfcflx.jclim05.pdf

I'm pretty sure you've misunderstood my question. I'm not looking for a direct link between ocean heat content and ocean surface temperature. I'm looking for the connection between those things and sea level.

Maybe this clarifies the above response.

Ocean Heat Content = integrated flux where flux is a function a bunch of parameters as described in the Cornell paper link, many of which you don't have measured parameters available with which to work. One of those terms is SST.

Sea Level = Ocean Heat Content * coefficient of expansion + Mass Terms

--- coefficient of expansion of water is temperature dependent so the first term is strictly an integral

--- Mass Terms include melting ice and large (typically seasonal) variations as evaporated water mass precipitates on land and takes some amount of time to get back to the sea

--- Melting Ice is not simply related to temperatures either as it involves glacier dynamics with long lags between cause and effect. I posted this article link up thread (

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2678

), the gist of which is that a particular glacier is apparently doomed to collapse, by itself contributing about a meter to sea level over perhaps the a few hundred years and if we could magically stop global warming tomorrow it's still likely to happen.

Thanks for all the info on this thread. I think this line of inquiry has run its course for me for the time being. All the best

Mean seal level has apparently fallen in the waters surrounding Tasmania:

http://morningmail.org/isle-of-the-dead/