From World Climate Report: Sea Level History Lesson
We are sure you’ve heard that sea level is rising? We conducted a web search on “Global Warming and Sea Level” and nearly 3.5 million websites are immediately located. And before you conduct the search yourself, you already know what you will find. The earth is getting warmer due to the buildup of greenhouse gases, the warmer sea water expands causing sea level to rise, and most of all, you will read all about the ice melting throughout the world pouring fresh water into ocean basins causing sea level to rise far more. Alarmists insist that the worst is just around the corner, and the sea level rise will accelerate or even quickly jump to a new level given some catastrophic collapse of large sheets of ice near the fringes of the polar areas. Coastlines will be inundated, the human misery will be on a Biblical scale, ecosystems will be destroyed … this goes on for millions of websites!
But things aren’t really so simple.
The United Nations’ IPCC group presents the graph below (Figure 1) regarding eustatic (or global) sea level over the past 125 years, and as noted by the IPCC and by many others, the rate of rise is definitely higher in the most recent 50 years than the first 50 years of the record. So, it becomes quite possible to suggest that sea level rise is accelerating, and may continue to accelerate in the future. Alarmists can certainly find material in the IPCC document to bolster their claim that sea level is not only rising, but the rate of the rise is increasing.
Figure 1. Annual averages of the global mean sea level based on reconstructed sea level fields since 1870 (red), tide gauge measurements since 1950 (blue) and satellite altimetry since 1992 (black). Units are in mm relative to the average for 1961 to 1990. Error bars are 90% confidence intervals. (figure source IPCC)
Back in August of 2008, scientists from all over the world attended a workshop entitled “Empirical Constraints on Future Sea-Level Rise” and they just published a summary of their findings in the Journal of Quaternary Science. Somewhere along the way, they decided to refer to the group as “PALSEA” for PALeo SEA level working group.
The PALSEA group begins their article noting:
The eustatic sea-level (ESL) rise predicted for the 21st century represents one of the greatest potential threats from climate change, yet its magnitude remains a subject of considerable debate, with worst-case scenarios varying between 0.59m and 1.4m. In general, the basis for this debate revolves around the uncertainties in the dynamical behaviour of ice sheets (such as loss of buttressing through ice shelf break-up or enhanced ice flow through water lubrication of the ice sheet base), which may lead to a nonlinear sea-level response to climate change.
Note that the authors are talking about worst-case scenarios leading to “0.59m and 1.4m”; if the trend of the past 50 years continues (from Figure 1), sea level will rise around 0.20 meters (around 8 inches) by 2100. The PALSEA team notes that measuring sea level can be tricky “Because changes in ice mass will also cause changes in regional (due to gravitational and rotational feedbacks) and global (due to volume) sea level, the changes in sea level at a particular coastline record the difference between vertical motions of the land and sea, commonly referred to as relative sea-level (RSL) changes. Such isostatic effects are a function of the distance from the large ice sheets.”
Now for the good stuff! The PALSEA team states that
Given a broad range of emission scenarios the IPCC AR4 predicted global warming of between 1.18C and 6.48C during the 21st century. The last time that a global warming of comparable magnitude occurred was during the termination of the last glacial period (TI).
Furthermore, they write
Given this evidence for periods of rapid warming during TI, at least some of this warming occurred on decadal to centennial timescales. Because of the general similarity between the magnitude and rate of warming predicted for the 21st century and the warming that occurred during certain periods of TI, it is interesting to consider rates of sea-level rise during TI as a case study of the response of sea level to climate change.
The PALSEA group presents the graphic below (Figure 2) showing three different rates of sea level rise following an increase in temperature. As seen there, sea level could rise exponentially (as suggested by many climate change alarmists), it could rise linearly, or it could rise and then level off (the “asymptoting” curve).
Figure 2. An illustrative sketch of three models (black) for the time-dependent response of sea level to a perturbation in temperature (red) (from PALSEA, 2010).
Here’s what they conclude:
Therefore, we suggest that option 1 (exponential sea-level rise) is extremely unlikely. …An exponential increase in rates of sea-level rise with respect to temperature would result in 21st-century sea-level rise an order of magnitude larger than estimates using alternative patterns of response – it is an important result that the palaeo-sea-level data rule out such a response.
Finally, they write “the palaeo sea-level data suggests that sea-level rise related to current warming may be rapid at first and slow over time.”
Basically, their analysis of what happened in the past favors the “asymptoting” curve that is quite different from the exponential curve favored by those proclaiming the worst is yet to come! Mother Nature showed us in the past how sea level responds to warming – we at World Climate Report are listening!
Reference:
PALSEA (the PALeo SEA level working group: Abe-Ouchi, A., Andersen, M., Antonioli, F., Bamber, J., Bard, E., Clark, J., Clark, P., Deschamps, P., Dutton, A., Elliot, M., Gallup, C., Gomez, N., Gregory, J., Huybers, P., Kawamura, K., Kelly, M., Lambeck, K., Lowell, T., Mitrovica, J., Otto-Bleisner, B., Richards, D., Siddall, M., Stanford, J., Stirling, C., Stocker, T., Thomas, A., Thompson, W., Torbjorn, T., Vazquez Riveiros, N., Waelbroeck, C., Yokoyama, Y. and Yu, S.) 2009. The sea-level conundrum: case studies from palaeo-archives. Journal of Quaternary Science, 25, 19-25.
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Are they saying that the “Asymptoting Sea Level Rise” we have experienced for the past 15K years is likely to continue for the foreseeable future – through the 21st Century? That’s what I thought. Nice to know that there really are a lot more levelheaded “scientists” out there than Mann,PennState&Co. would have us believe. Universities really do deserve to be known by the faculty they keep. I think it’s too late to do anything for East Anglia.
Espen: Many thanks for going to the trouble of getting that table for me. I’ve made a note of it and will look carefully at it. This site really does attract the best people! Dave.
Observations v models (from the Australian CSIRO).
<blockquote"Recent observations show the observed sea levels from tide gauges (blue) and satellites (red) are tracking near the upper bound (black line) of the IPCC 2001 projections (grey shading and black lines) since the start of the projections in 1990 (Rahmstorf et al. 2007). This upper limit leads to a global-averaged sea-level rise by 2100 of 88 cm compared to 1990 values. These observations do not necessarily indicate that sea level will continue to track this upper limit – it may diverge above or below this upper limit. However, the ice sheet uncertainties referred to above are essentially one-sided – i.e. they could lead to a significantly larger sea-level rise than current projections but are unlikely to lead to a significantly smaller rise."
http://www.cmar.csiro.au/sealevel/sl_proj_obs_vs_proj.html
Millennial and centennial time series from the same source:
http://www.cmar.csiro.au/sealevel/sl_hist_few_hundred.html
(In reference to recent comments here. e.g, Rahmstorf et al 2007 projections, in the IPCC 2001 assessment, were less than observations)
DaveF says:
August 10, 2010 at 10:49 am
“Packbear: The UK and France may not have had the sea between them but I suspect there was a really big river to cross. The Rhine, aided and abetted by the Seine and the Thames, in summer, would have had to go somewhere.”
The Rhine and Thames probably went North, to enter the Arctic Ocean alongside what is now Norway. The Seine probably went West, down what is now the English Channel. That would leave a dry landbridge between England and France across the Strait of Dover. I don’t know whether there’s any hard geological or archeological evidence for (or against) this. If anyone knows of any perhaps they could mention it?
And the English can probably thank Joan of Arc for not becoming a department of France once The Kings’ English became Les Rois Français …
Paul Birch: The Rhine couldn’t have gone north because the UK and the area which is now the top and middle of the North Sea had half a mile of ice on it. I believe there is still a current from the mouth of the Rhine that flows along the bottom of the English Channel. The Thames would have had to go south, too, but probably only flowed for few weeks in summer. Of course, you could have walked across the ice from Denmark, and I daresay hunters did so, but you’d have had to watch out for those nice, cuddly polar bears! Best wishes, Dave.
DaveF says:
August 11, 2010 at 10:32 am
“The Rhine couldn’t have gone north because the UK and the area which is now the top and middle of the North Sea had half a mile of ice on it. I believe there is still a current from the mouth of the Rhine that flows along the bottom of the English Channel. The Thames would have had to go south, too, but probably only flowed for few weeks in summer. Of course, you could have walked across the ice from Denmark, and I daresay hunters did so, but you’d have had to watch out for those nice, cuddly polar bears! Best wishes, Dave.”
I do see what you mean about the ice. However, I don’t see how there can be much of a bottom current from the Rhine to the English Channel now; there’s too much shallow water in the way. Ditto from the Thames. The undersea contours don’t look right (ridges across the way the rivers would have to flow). They were probably even less suitable back then, because the trough of relatively deep water in the middle of the Dover Strait was pretty obviously created by tidal scouring as the landbridge submerged. But both the Thames and the Rhine could have found a route East towards Denmark, then up to the Skagerrak, where a tongue of the Arctic Ocean forms a deep channel. Even when sea level was at its lowest, that would have provided a viable exit under the ice. The undersea contours do look about right for that (though I realise that they must have changed considerably since then).
pouncer August 10, 2010 at 3:30 am:
“I’m not in any way convinced the sea levels are prone to catastrophic rise… And in the absence of oceans overwhelming the current coast line — exactly what is bad about warming?”
To pouncer and others. I recommend Mark Lynas “Six Degrees”. It is an informative, accessible, well researched read about what might reasonably be expected to occur should mean global temperature rise 1C, 2C, 3C, 4C… The author is a believer in AGW but does not predict any particular temperature increase (despite the “alarmist” sounding title). Chapters post 4C become progressively speculative as supporting data sets become sparser.
My perception is that threats to agriculture will prove far more disruptive than sea level rise. From p96 in the “two degrees” chapter: “the two degree world will see escalating challenges as crop-producing areas struggle to adjust to a warming climate”. So, at only +2C, the world’s food producing capacity for our ever growing population will likely come under stress. Given that paleo studies indicate a doubling of CO2 will result in a 3C (+/-1C) rise I find this assessment very sobering.
Beyond 2C the variety and magnitude of changes will pose potentially insurmountable problems, especially in many poorer parts of the world. Some will no doubt dismiss this post as misguided, alarmist propoganda driven by blinkered dogma. To those with a genuine interest in “what is the big deal if temperatures rise anyway?” please take the time to read “Six Degrees” and follow up on some of its research paper references.
Here’s a speculative hypothesis: what if rising sea level reaching a certain level triggers the end of the interglacial? e.g. by causing a shift in ocean currents and upwelling? Is there any data on sea level at the terminations of other recent interglacials?
it is an important result that the palaeo-sea-level data rule out such a response.
It is an important sign of progress that a climate related study actually checks an AGW related hypothesis against palaeo data.
How close are they to making the next logical step: palaeo climate data (e.g. temps, CO2) rules out CAGW?
Ref – e.g. The current WUWT post on mesozoic period with similar climate to now but 10+ x more CO2
The Sydney Morning Herald has run an article, 12/8/10, quoting scientists calcuate rises to exceed 7 meters!!!! and has an overalay of the ice-shelf over the state of NSW.
The researcher/journo has obviously not got to these details as yet.
check it out.
macha (WA)
Paul Birch: This is from Wikipedia. Article “The Rhine”, paragraph “Ice Ages”.
“The last Ice Age……..(Last Glacial Maximum). During this time the lower Rhine flowed roughly west through the Netherlands and extended to the south-west, through the English Channel, and finally to the Atlantic Ocean.”
Before the Ice Ages it flowed north, apparently, but I meant during the last Ice Age. Best wishes, Dave.
DaveF says:
August 12, 2010 at 2:31 am
“This is from Wikipedia. Article “The Rhine”, paragraph “Ice Ages”.”
Thanks for that. It has obviously been claimed that ice dammed up the Rhine’s northern exit to the Arctic, causing the Rhine to break out into the English Channel, but the claim doesn’t seem to hold water (!). In this glaciation, the westernmost part of Jutland was apparently ice free, or at the western edge of the Scandinavian ice sheet. “Doggerland” was apparently tundra, so there was a clear route for the Rhine to the deep water ocean channel. I find it hard to see how that exit could have been completely blocked. Even if an ice shelf extended over that channel (which the maps don’t show) that wouldn’t stop the river continuing to flow beneath it. Not even if the shelf became thick enough to ground; the river flow would still keep the channel open, or re-open it if an ice-fall somehow blocked it. The only evidence for the claim seems to be the scoured channel in the Strait of Dover – but tidal scouring could manage that quite effectively without any catastrophic flood. There are just such channels around the Isle of Wight. I remain to be convinced.