Thursday, June 25, 2015

The Question Is: How Much Acceleration Is Involved In SLR - 8?

Fig. 1 Arctic sea ice extent / area 6/27/15

In this series I have pointed out that sea level rise (SLR) projections must consider acceleration of the volume of ice sheets that are entering the oceans per year.

The old way of linear projections, by older software models, has been proven to be wrong.

Those models have consistently underestimated the rate of SLR caused by loss of ice volume on Greenland and Antarctic ice sheets.

So, Greenland and Antarctic ice sheet volume loss, in terms of contribution to SLR, is now determined by rate of acceleration of ice volume lost per year.

If the old models continue to be used, their linear formulas will faithfully underestimate the rate of loss of ice volume at the ice sheets of both Greenland and Antarctica (The Question Is: How Much Acceleration Is Involved In SLR?, 2, 3, 4, 5, 6, 7).

The exercise becomes, then, an issue of how much acceleration of ice volume loss is taking place (ibid, cf. The Evolution of Models, 2, 3, 4, 5, 6, 7, 8, 9, 10).

II. "Doubling" Is Another Way of Saying "Acceleration"

In general, acceleration is difficult to determine using only a year to year basis.

An alternate method of projection has been expressed by top scientists in terms of "doubling" of ice volume loss over some span of time:
The effect that 2, 3, 5, 7, and 10 year doubling has is that it determines when SLR reaches the 1 m / 3 ft. level:
10 yr = 2067
7 yr = 2055
5 yr = 2045
3 yr = 2035
2 yr = 2031
(The Question Is: How Much Acceleration Is Involved In SLR - 5?).  We focus most on 1 m / 3ft. because it is a point where many locations that are tidal will experience serious problems, especially with coastal infrastructure and ports (The 1% May Face The Wrath of Sea Level Rise First).
(The Question Is: How Much Acceleration Is Involved In SLR - 7?). That "1 m / 3ft." level of SLR will be reached at a time that is dependent on the rate of acceleration of ice volume loss.

If acceleration of the amount of land ice which reaches the ocean, in the form of melt water or icebergs, doubles each two years from now on, then that "1 m / 3 ft." level of SLR will take place circa 2031, but if it doubles each 10 years from now on, then that "1 m / 3 ft." level of SLR will take place circa 2067.

III. Catastrophe Is What We Want To Avoid

Since that "1 m / 3ft." level of SLR is the catastrophic level, that is what we must keep our eyes on.

What will happen at that level and above is "unthinkable" (Greenland & Antarctica Invade The United States, The 1% May Face The Wrath of Sea Level Rise First, Why The Military Can't Defend Against The Invasion, Why Sea Level Rise May Be The Greatest Threat To Civilization, 2, 3, 4).

It would change civilization as we have known it (Weekend Rebel Science Excursion - 44, Will This Float Your Boat?, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11).

IV. The Wildcard Is "The Surge"

I found scientific papers which examine the evidence for historical surges in SLR (The Surge: A Forgotten Aspect of Sea Level Rise).

Surges or "pulses" are abrupt increases in acceleration of SLR.

The evidence indicates several surges in SLR (e.g. "Pulse 1A ... 1B and 1C") in the paleoclimatology records of ice cores, soil strata, etc. (ibid).

The larger the increase the slower they tend to be, taking more time to happen.

The only surge I am interested in is "pulse 1C", a "1 m / 3 ft." SLR which took place about 7-8,000 years ago, which left marks and other evidence in North America.

It is the most interesting surge, because "1 m / 3 ft." of SLR was all said and done in "a few years or less" (ibid).

Two vast lakes of melt water had been held back from entering the ocean by an ice dam which eventually collapsed as temperatures warmed, releasing all that water into the ocean.

There are no vast lakes now, but there are hundreds of "moulins" where melt water flows under Greenland's ice sheet and then disappears (The Question Is: How Much Acceleration Is Involved In SLR? - 4).

It is not known whether or not the water is being captured in sub-glacial canyons, thereby creating lakes, or is flowing out into the ocean.

Similar events now take place in Antarctica too (ibid).

V. We Know Less About Critical Issues Here Than There

As late as 2005, it was written:
"In spite of its importance, the mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is poorly known; it is not known whether the ice sheet is growing or shrinking."
(The Agnotology of Sea Level Rise Via Ice Melt). We know more about the ice caps on Mars it would seem.

Yet, Greenland and Antarctica have enough ice sheet volume that if only 1.14% of their ice melts or otherwise makes it to the ocean, we will have the catastrophe that a "1 m / 3 ft." SLR can bring about (Why Sea Level Rise May Be The Greatest Threat To Civilization - 4).

We seem to know more about other planets, moons, comets, and the like, than we know about the planet where we are (You Are Here).

VI. There Is Some Uncertainty About "When"

The non-linearity mentioned in the Introduction means that we are made somewhat uncertain as to the timing of events by the nature of those events.

Notice Fig. 1, which shows that this year's Arctic sea ice extent or area was the lowest on record for several months, but has, as of a few days ago, fallen into second place (but "it ain't over 'til its over").

The year of record for lowest extent, 2012, was also a year of extreme melt events on the surface of the Greenland ice sheet.

During the years since then, we have not had those same record breaking events.

The point is that there are both surges and then non-linear years (not the same ice volume loss as the year before) following surges, where ups and downs take place.

Having said that, it is not the same as saying the ice volume loss stops.

Loss continues in a non-linear fashion, but overall there is an acceleration in the loss of ice volume in both Greenland and Antarctica (the ice volume loss graph line trend is upward).

VII. Conclusion

Even though there have been popular events such as the Papal encyclical, the view from astute observers is still quite pessimistic realistic (Greenland & Antarctica Invade The United States - 2).

Realistic in an extinction kind of way.

The previous post in this series is here.

David Puttnam on climate change:

No comments:

Post a Comment