Discussion:
estimating Antarctic seaice thickness
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k***@gmail.com
2024-09-05 18:31:37 UTC
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A surprise result just shot out of one of my AI programs.

Mostly they while away their time scanning that Internet thing for
data and trying to "understand" the world. Understand involves being
able to make accurate predictions. Predictions are statements that
take some data and calculate other data that has been "validated".
Validation involves building a model on some of the available data and
then ensure it actually predicts things by testing it on the rest of
the data. Old-fashioned statistical models are not much good at
prediction because they mostly "remember" the data they were given and
don't have any way to generalise it for new conditions -- even ones
that are only slightly different from the data they were given.

Anyway. The object of their exercise was to predict seaice thickness
given the data they had to hand. For the N Hem this is a little easier
because a greater diversity of data has been gathered for the region.
Using a couple different datasets and some smoothing operations
calculating seaice thickness in the Arctic is fairly straightforward.

But for the Antarctic we have a problem. It hasn't been monitored all
that closely in the past and even now the datasets available are much
less detailed than for the Arctic.

But the AI's have discovered a simple model they can show predicts
Arctic seaice thickness and is validated against a couple different
estimates of thickness produced by the UW and one of my programs
AMAZINGLY also seems to work when transferred to the Antarctic.

The model for the N Hem is thus:

Variable Coeff Stderr Tval Pval
date -0.01994 0.00415 -4.79946 0.00003
logN 1.86036 1.07879 1.72450 0.09296
Narea 0.10751 0.06834 1.57316 0.12419
aravgArcocean 0.11962 0.04633 2.58210 0.01391
CONSTANT 36.10241 10.28203 3.51121 0.00119

The "date" in this case is the year/month given as a number with 2dp.
logN means log(Arc extent in mns km2), Narea is Arc area in mns km2,
aravgArcocean is the avg temp of the Arc ocean as given by the NOAATEMP.

The model for the NH gets the thickness to within +-10% for any given
year in the data and was validated on a 50/50 basis -- i.e. the model
was estimated on the first 1/2 of the dataset and validated on the 2nd
half and still produced numbers within +-20% of the "actual" value.

And the amazing part is when transferred to the Antarctic the numbers
that come out also look amazingly similar in value and trend to the
Arctic. The model doesn't seem to go out of rational range and shows a
gentle decline in seaice thickness as seen in the Arctic.

So we seem to have estimates for seaice in the N and S that look like this:

Year Arcth Antarcth
(m) (m)
1979 2.2950 2.14137
1980 2.2639 2.01899
1981 1.9643 2.051
1982 1.8963 2.06484
1983 2.0675 1.99052
1984 2.0983 2.00235
1985 2.1322 2.01453
1986 2.1629 1.8393
1987 2.1562 1.95019
1988 2.1507 2.07631
1989 2.0805 1.88978
1990 2.1097 1.85941
1991 2.1045 1.8648
1992 2.0251 1.81004
1993 1.9524 1.79669
1994 2.0171 1.87097
1995 1.9117 1.83792
1996 1.8978 1.8109
1997 2.0448 1.7139
1998 1.9721 1.7666
1999 1.9512 1.73691
2000 1.8327 1.74199
2001 1.9736 1.67394
2002 1.8516 1.56555
2003 1.7900 1.73269
2004 1.7579 1.7116
2005 1.7601 1.60587
2006 1.7366 1.54402
2007 1.5263 1.58708
2008 1.6306 1.68118
2009 1.5151 1.61483
2010 1.2694 1.60398
2011 1.2365 1.42929
2012 1.2078 1.55498
2013 1.2962 1.66682
2014 1.4741 1.69367
2015 1.3901 1.56688
2016 1.2918 1.26981
2017 1.1513 1.15035
2018 1.2449 1.17626
2019 1.1730 1.14922
2020 1.2750 1.31146
2021 1.2582 1.25081
2022 1.2552 1.01683
2023 1.3274 0.804207

--
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R Kym Horsell
2024-09-05 18:46:52 UTC
Permalink
Post by k***@gmail.com
A surprise result just shot out of one of my AI programs.
...
Post by k***@gmail.com
2021 1.2582 1.25081
2022 1.2552 1.01683
2023 1.3274 0.804207
Just a footnote. The "0.804" there is the model's prediction of
avg seaice thickness in the Antarctic over 2023.
In the Arctic experts say the 1m thickness is a red line.
If seaice averages less than that it can't survive a freeze/melt
cycle over 12m. It's expected when enough months average under 1m
in the NH there will be a "blue water event" -- usually defined
to be seaice less than 1 mn km2 (it will mostly be "fast" ice attached
to the coast).

I'm nore sure what the numbers are supposed to be in the Antartic.
Already summer seaice is very low compared with the Arctic.
If the model that predicts Arc thickness seems to transfer down
to the SH (by changing N->S andf Arc to Antarc in the variables used
in the calculations) then it may be its prediction that seaice in
2023 averaged less than 1m thick and we are due for a bluewater month
anytime now in the Antarctic.

From other posters I hear daily seaice in the Ant is looking lower
and lower. So bluewater could be a live option.

Ominously from the NASA Realtime estimates of Antarctic seaice
(they took over from the Goddard climate group in processing
the relevant sat data about 2y back now and there was a slight glitch
in the dataset because the new calculations are just a little different
from Goddard's version) the minimum monthly avg extent in 2023 for the
first time came in under 2 mn km2. Again, suggesting 1mn km2 or less
is due in the next few years aka "bluewater".
--
Psychologists have determined some people are terrified of math.
By attaching electrodes to the legs of experimental subjects, then
feeding them problems like adding up a column of numbers, they found
thinking about math caused unconscious flexing of muscles normally
used for running.
They found math triggered at least the "flight" part of the fear
response.
Why would a psychologist do that? I hear someone in the audience ask.
Answer: Because it's fun!
Addendum: It's speculated some people exhibit the same kind of
response in any learning situation. C.f. Dunning and Kruger's work on
(in)competence.
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