|Totten Glacier: when is sea level rise prediction real?|
One series of posts at Dredd Blog gives an indication of some difficulties that repeatedly arise.
Difficulties that arise any time anyone seriously and honestly wants to be accurate about future Sea Level Rise (SLR) on planet Earth, and the impact that SLR will have on civilization.
Yes, when one wants to be accurate enough to present a reliable projection of SLR that even Goldilocks could "live with," which is, not too high and not too low, but "just right."
That Dredd Blog series is Will This Float Your Boat, 2, 3, 4, 5, 6, 7, which shows that Goldilocks is not going to be very happy with the results, no matter how those projections might eventually end up.
What I want to do here, then, since this blog has far fewer posts compared to Dredd Blog, is to condense the dynamics involved into a simple description of some of the techniques being used to calculate future SLR.
The exercise is not to discover "what technique would Goldilocks subscribe to," because, we are concerning ourselves with projections of future SLR.
Remember that Goldilocks only worked with the exact present, not with the less certain future, so, she could make ultimate conclusions that were ultimately accurate.
But, we can be scientific and comprehensive, which generally requires us to be empty of fear, underestimation, and overestimation, to a reasonable degree.
II. Question: What Is At Stake First?
We can ask the ultimate question for the future, which is, "how much SLR will it take to bring down current civilization?"
Which begs the question: "what do you mean 'civilization'?"
That question has been asked and answered previously in 2009:
World civilization means the nations of the world interconnected by trade, travel, treaties, and international commerce.(What Do You Mean - World Civilization?). Civilization, in the sense that it is something being damaged by SLR, is a realm of trade in high volumes of goods and services.
So, when climate change scientists talk about dangers to the existence of civilization they do not mean that the population of human beings as a species is going to become extinct.
In other words, the human species would live on even if civilization ended.
For example, Greenland alone has enough ice that if that ice was to melt it
would raise the world's ocean level by 21 feet (7 meters).
Fig. 1 (click to enlarge)
That alone would destroy the ocean-port cities of the civilized world, and thereby destroy world civilization by destroying its primary commerce.
But if you add Antarctica to the equation, much more than just the coastal ports would be lost, because the ocean level would rise beyond belief.
Scientists have not been worried about Antarctica before 2006 when it was shown that some of its western ice sheet was getting a bit shaky.
The eastern ice sheet, however, was considered to be "inviolate", meaning "not to worry", nothing will ever happen to it.
But like many things climate scientists considered to be "inviolate", the eastern ice sheet of Antarctica is now going somewhere ...
Goods and services that are constantly being negotiated 24/7 between and among nations around the globe.
A three-foot SLR, IMO, will curtail that commerce abruptly.
That is because the seaports, where international commerce takes place and where goods are shipped and received incessantly, will be impaired by SLR.
Civilization, as we know it, will go through changes to the point that we will not easily recognize it as the civilization it once was, once SLR gets done with it.
Stop-gap measures (such as air freighting everything, or anchoring cargo ships off shore, then ferrying smaller amounts to shore with a flotilla of smaller vessels), won't be sufficient enough to keep prices, delivery schedules, and the like, "economically civilized" as it is now.
III. One Method of Graphing Future SLR
The technique used to generate a graph below, (Fig. 3), begins by using the USGS data (Fig. 1 above) indicating the maximum SLR possible from ice melt at various locations around the globe.
Second, we calculate the current melt rate of ice taken by a satellite, Cryosat-2, specifically designed and put in orbit for that purpose:
Measurements from ESA’s CryoSat mission have been used to map the height of the huge ice sheets that blanket Greenland and Antarctica and show how they are changing. New results reveal combined ice volume loss at an unprecedented rate of 500 cubic kilometres a year.(ESA Cryosat, emphasis added). Next, we use a formula to reduce the 2009-2013 exact measurements, done by that satellite, into a useful acceleration percentage:
The resulting maps reveal that Greenland alone is reducing in volume by about 375 cubic kilometres a year.
The researchers say the ice sheets’ annual contribution to sea-level rise has doubled since 2009. [Table 1 type contribution - i.e. thermal sea level rise (additional) is not included in that doubling]
Glaciologist Angelika Humbert, another of the study’s authors, added, “Since 2009, the volume loss in Greenland has increased by a factor of about two and the West Antarctic Ice Sheet by a factor of three."
L = [ (f / s)(1 / y) ] - 1 :Next, the 14.87% acceleration rate for that time frame is used pro rata on the various locations, using each SLR value provided in Table 1 above (USGS data) as the applicable SLR in a given area on which that acceleration takes place.
L = acceleration of ice-volume-loss per yearL = [(500/250)(1/5)] - 1
f = final volume of loss-per-yr (~500 km3)
s = starting volume of loss-per-yr (~250 km3)
y = number of years (~5)
L = (2.2) - 1
L = 1.148698355 - 1
L = .148698355
L = 14.87% annual ice loss increase 1/1/09 - 12/31/13
2009) 250 x 1.148698355 = 287.17458875
2010) 287.17458875. x 1.148698355 = 329.876977695
2011) 329.876977695 x 1.148698355 = 378.929141631
2012) 378.929141631 x 1.148698355 = 435.275281653
2013) 435.275281653 x 1.148698355 = 500.000000006
Ok, that checks out.
That is, we can extrapolate and apply that acceleration rate to SLR values, at each location, based on their percentage of global SLR (e.g. Greenland has a 21.49 ft. maximum SLR, while W. Antarctica has a 26.44 ft. maximum SLR).
One caveat here is that this acceleration rate, which actually doubled the ice volume loss in 5 years, could be a surge.
That is, it may not be a continuing acceleration rate, so we must watch that rate from time to time, then make adjustments accordingly if the rate fluctuates.
IV. The Melt Zones
Another factor, involved in graphing future SLR, is that Greenland and Antarctica have zones where various rates of melt, or no melt, are taking place at different times, or at the same time.
|Fig. 2 (click to enlarge)|
The gist of it is that melt of various sorts is ongoing both sequentially and concurrently.
The coastal zones began, or will begin, to melt first in each location.
Later, peak melt is reached, then it gradually subsides, until all the ice in that zone has melted into water, which then flows into the ocean (causing SLR).
Meanwhile, another zone further inland begins to melt, peak, subside, and so on and so forth.
The difficulty is to know when the melt begins, peaks, and subsides completely, which is why we call the software (which generates the values we use to make the graphs) a "model."
On the bright side, beginning with known values makes the models work better, even in those mysterious "when" zones of future melt, and subsequent SLR.
V. A Graph To Test The Model
The graph, Fig. 3, is a model projection which extends out to the year 2200, which, as you can see, has some lines that end abruptly.
|Fig. 3 (click to enlarge)|
That happens when the USGS figures for maximum SLR, in a particular location, have been reached.
For example, Greenland's line will stop when 21.49 feet of SLR has taken place, and areas with lesser SLR values will stop sooner, eventually leaving only the line for Antarctica (because it does not all melt in the graph's time frame).
This is not as shocking, at first blush, as one might think if a quick computation is made.
A computation based on a recent scientific observation that for every 1°C of global temperature rise, there is a ∼2.3 meter SLR (Strauss PNAS, PDF, cf Potsdam Institute).
A 4°C rise in temperature is expected before 2100 (ibid), which equates to a 9.2 meter SLR (4 * 2.3 = 9.2).
The 9.2 meter SLR equates to a 30.1837 ft. SLR (9.2 m = 30.1837 ft.).
The Fig 3 graph above, generated by the model's projection algorithm, indicates a 21.0734 ft. SLR by 2100 (software model's print out for that year: "2100, .... , 21.0734").
That is 9.1103 ft. (30.2%) below the 30.1837 ft. maximum potential SLR implicated by a 4°C rise in temperature.
Which is not inconsistent, because some delay between temperature rise and SLR is to be expected.
But the timing of the delay (how much when), is not easy to calculate because of all the variants.
Nevertheless, we do know, by Cryosat-2 measurements, that 500 cu. km3 of ice is currently melting each year.
It was only 250 cu. km3 in 2009, so the melt amount doubled between 2009-2013, which is a 14.87% acceleration rate as shown above in Section III.
So, the projected melt in the model that produced Fig 3. seems to be reasonably within maximum SLR expectations.
During the 85 years of that quantity of ice loss between now and 2100, a significant acceleration of temperature also means an acceleration of ice melt.
The three foot level I talked about, in Section II above, is shown on the graph (Fig. 3) as taking place in 2033, a little less than two decades from this year (2015).
But, SLR does not stop there does it?
That, if accurate, clearly shows why global warming induced climate change has been called, by the President and the Pentagon, the number one threat to national security.
The previous post in this series is here.