Sea level 2000 years

Here is the global sea level thread focused on the last one or two thousand years. Mojo in ’50 to 1’ has not found the time to start us up here with a new thread as I requested. So, I did it.


What purpose could it serve? When the air is warmer, grounded ice cannot avoid melting, and seawater can only expand in volume. This is physics. So we should ask, were sea levels higher during those earlier times?


Paleo air-T proxy results that mojo and I mentioned in the ’50 to 1’ thread have previously been summarized in two ways: (a) Medieval was warmer than now, or (b) no, it wasn’t. I am not undertaking the task of re-summarizing those many studies. Neither is our mojo, apparently. He is satisfied sending us to websites where he gets his spoon feeding. So, I already said that we are at an impasse on Paleo T, in ’50 to 1’; but that could be advanced by anyone wanting to delve into the many details. Perhaps it will happen.


Sea level should have risen in those earlier times, if warmer times they were. ‘Should’ is an understatement here! If earlier times weren’t warmer, sea level wouldn’t have been higher. Sea level is a process integrator, not a proxy. The difficulty is to actually measure sea level on kiloyear scales, demonstrate convincingly that it was measured it correctly, and correct for any geological uplift or subsidence (together called isostatic adjustment in the literature) that could have been happening at the measurement sites.


Few studies have actually done this (few in comparison to the many Paleo-T proxy studies). While we always wish for more, this fewness may work to our advantage. Auditing hundred or thousands of Paleo-T studies would be a daunting task.


Just we might have expected IPCC AR5 offers an historical sea-level summary, in the WG1 chapter 13 draft now posted at

http://www.climatechange2013.org/report/review-drafts/


along with all the others from Working Group 1. Those documents are still called “do not quote or cite” so let us imagine that I have done neither here. If the AR5 draft material I present is changed in the final published report, it will be my responsibility to clean that up later.





Figure 13.3: (a) Paleo sea level data for last 3000 years from Northern and Southern Hemisphere sites. The effects of glacial isostatic adjustment (GIA) have been removed from these records. Light green = Iceland (Gehrels et al., 2006), purple = Nova Scotia (Gehrels et al., 2005), bright blue = Connecticut (Donnelly et al., 2004), blue = Nova Scotia (Gehrels et al., 2005), red = United Kingdom (Gehrels et al., 2011), green = North Carolina (Kemp et al., 2011), brown = New Zealand (Gehrels et al., 2008), gray = mid-Pacific Ocean (Woodroffe et al., 2012).



Cited above:



Donnelly, J. P., P. Cleary, P. Newby, and R. Ettinger, 2004: Coupling instrumental and geological records of sea-level change: Evidence from southern New England of an increase in the rate of sea-level rise in the late 19th century. Geophysical Research Letters, 31.



Gehrels, W. R., et al., 2005: Onset of recent rapid sea-level rise in the western Atlantic Ocean. Quaternary Science Reviews, 24, 2083-2100.



Gehrels, W. R., et al., 2006: Rapid sea-level rise in the North Atlantic Ocean since the first half of the nineteenth century. Holocene, 16, 949-965.



Gehrels, W. R., B. Hayward, R. M. Newnham, and K. E. Southall, 2008: A 20th century acceleration of sea-level rise in New Zealand. Geophysical Research Letters, 35.



Gehrels, W. R., D. A. Dawson, J. Shaw, and W. A. Marshall, 2011: Using Holocene relative sea-level data to inform future sea-level predictions: An example from southwest England. Global and Planetary Change, 78, 116-126.



Kemp, A. C., B. P. Horton, J. P. Donnelly, M. E. Mann, M. Vermeer, and S. Rahmstorf, 2011: Climate related sea-level variations over the past two millennia. Proceedings of the National Academy of Sciences of the United States of America, 108, 11017-11022.



Woodroffe, C. D., H. V. McGregor, K. Lambeck, S. G. Smithers, and D. Fink, 2012: Mid-Pacific microatolls record sea-level stability over the past 5000 yr. Geology, 40, 951-954.



Before considering what might have been excluded from this AR5 draft graph, please look at it. Since 3000 YBP, sea level overall has been constrained to -0.6 to +0.2 m compared to current sea level. Woodroffe et al. 2012 data are flat. Donnelly et al. 2004 (local to NE US) provides the best hope for people ‘hoping that’ ~800 YBP sea level was higher.



Next I refer to my post from the ‘50 to 1’ thread, concerning Gehrels et al. 2005, which was also cited in the AR5 draft. Those author’s graph of local sea levels during medieval did not show a bump, and referred to two earlier local studies that also did not:



Gehrels, W.R., Belknap, D.F., Black, S., Newnham, R.M., 2002. Rapid sea-level rise in the Gulf of Maine, USA, since AD 1800. The Holocene 12, 383–389.



van de Plassche, O., 2000. North Atlantic climate–ocean variations and sea level in Long Island sound, Connecticut, since 500 cal yr AD. Quaternary Research 53, 89–97.



I read all these to indicate that we haven’t strong evidence of a medieval sea-level bump. However, if there is any contrary evidence from any local site, we should consider it in this thread.



The uncertainty expressed in the AR5 figure above does not preclude +0.2 meters change over hundreds of years during MCA, nor a similar reduction over similar time scales after. That could have happened. But I would ask PC readers to compare such < 1 mm/yr rates to the 20th century, which started at < 2 mm/yr and grew to > 3 mm/yr at the end.



Future sea-level rise rates are not for us to know, but if the largest fraction of atmospheric IR-trapped energy continues to accumulate in the ocean, SLR rate will increase. Damn physics.



Let us use this thread to examine individual studies of sea-level history over the recent few kiloyears, locally or globally. Let us not be constrained by studies cited in the IPCC AR5 draft.



Here is another study I have seen:



Glenn A. Milne, W. Roland Gehrels, Chris W. Hughes & Mark E. Tamisiea. 2009. Identifying the causes of sea-level change. Nature Geoscience 2, 471 – 478. doi:10.1038/ngeo544



Their Fig. 3b. shows flat sea level over the last 6000 years, and 3c. from 500 to 200 years ago (not quite long enough for our purpose here). 3b. was attributed to:



Woodroffe, S. A. Reconstructing sea-level changes in North Queensland, Australia, using a foraminifera-based transfer function. The Holocene, in review (2008).



Which appears to have been published as:

Recognising subtidal foraminiferal assemblages: implications for quantitative sea-level reconstructions using a foraminifera-based transfer function

Sarah A. Woodroffe

Journal of Quaternary Science

Volume 24, Issue 3, pages 215–223, March 2009



But I do not find the figure with paleodates in that paper – just (flat) reconstructed sea level vs. depth in the core. I have no further information about that.



Fig. 3c. came from Gehrels et al. 2008, which was included in the IPCC figure I included above.



What isn’t in the IPCC figure above, nor in the other studies I’ve mentioned, is evidence (local or otherwise) of an MCA increase followed by a decline. Some might take that to mean that studies have been left out of the IPCC chapter, in which case it should be a simple matter to list the citations here. Already said my guess that the total number won’t be large. It should then be a simple matter to see if they have ‘got the goods’. Or possibly hit one of the pitfalls, such as not correcting for geological uplift or subsidence.



I steadfastly continue not discussing Grinsted et al. 2009 (presented as supporting C3 website aims in the 50 to 1 thread) until someone else here reads it and says something about it. Mojo has said he doesn’t know why they used Moberg et al 2005 paleo-T, which seems to indicate he doesn’t know the several T reconstructions that they did use. I have ideas about that study, but I don’t want to push them into your heads. Spoon feeding is not the right thing for adults.

 

The current SLR (3 mm/yr) is thirdsies. 1/3 polar ice (incl greenland) 1/3 continental ice, 1/3 thermal expansion. The independent measures of those three equal independent measures of SLR. When data 'hangs together' one may experience a feeling like comfort. When there are jarring inconsistencies, no comfort. More work needed.

It's really not until reading the paleo SL papers that one gets the idea of how hard it is to do. So, while I am hoping for more, I don't think that the number will increase rapidly.

 

The new paper I refer to here is about more than 2000 years, but this is newest sea level thread, so here it goes

"A geological perspective on potential future sea-level rise"

DOI: 10.1038/srep03461

it is open access, as everything in the (Nature subsidiary journal ) "Scientific Reports".

Have a look. My summary is that as we have unusually rapid CO2 rise now, sea level rise has not caught up. (Even Mojo can tell you that ice melts slowly). It will catch up, later. This century, the authors expect 0.9 meters, or less. Later, they expect more.

Getting a more rapid SLR than that would be unusual in the geological context. But, so is the rate of CO2 increase, so there you go.

Hoping that the sensitive areas in Greenland and Antarctica manage to hold. In any case, it seems appropriate to take a look at those coastal defenses. Except in North Carolina, where rapid SLR is prohibited by law Youse guys have nothing to worry about.