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Han

(Scott Lurndal) wrote in
:

Han writes:
Doug Miller wrote in
0:

Han wrote in news:XnsA0847BD6DC6C5ikkezelf@
207.246.207.124:

One of the scary reasons to pay attention to ocean warming is
that much is really cold (like in the 30's and low 40's in
Fahrenheit). If all that ocean water warms just a few degrees, it
will expand, and thus the level will go up. Somebody ought to have
the calculated data how much up that up is.

Not scary at all to anyone who's had an education in the physical
sciences.

Water has its maximum density of 1.00000 g/ml at 3.98 degrees C. At
5 deg C (41 deg F) its density is 0.99999 g/ml, and at 10 deg C (50
deg F) the density is 0.99973 g/ml -- IOW, warming from 4 deg C to
10 deg C, water will expand by a factor of (1.00000 / 0.99973) =
1.00027, or about one-fortieth of one per cent.

Water is actually more dense at 5 deg C than at 0.

[Source for the above data is the Handbook of Chemistry and Physics]

My Handbook is upstairs. One of the very few books I took when I
retired. It is really old, though still the larger format.

OK, let's do the calculations.

First let's assume that the ocean basins don't change in volume as the
ocean warms up.

From http://ngdc.noaa.gov/mgg/global/etopo1_ocean_volumes.html
total volume: 1,335,000,000 km^3
Total surface area 361,900,000 km^2

Using your expansion factor as a very large approximation:
Total volume becomes 1,335,000,000 * 1.00027 = 1,335,360,450 or
360,450 km^3 more, which is divided over an area of 361,900,000 km^2.
That is a height of 0.000995993368 km, i.e. 99.59 cm or over 3 feet.

Your temperature rise is very large, so with a lower rise in
temperature, the rise in sea level won't be as great. But, keep in
mind that this is only the effect of warming of the whole ocean. I
don't (yet) know what the expansion will be on average, because I
don't know how fast a) the oceans will heat up, and b) how fast the
oceans mix. However, we need to add the effects of glacier and icecap
melts, and we have no idea really how the rate of melting is going to
change. Overall (and there are vast variations), that rate seems
likely to increase, rather than decrease.

Of course, a couple of dozen Mt Pinatubo sized volcanic eruptions will
likely cool things down for at least a few years, let alone Krakatao-
sized ones ...

There are a number of factors that need to be considered when
thinking about the average sea level:

1) Isostatic rebound; some land surfaces in the Northern Hemisphere
are still
rebounding (rising) from the last ice age. All things equal,
this results in relative lowering of sea level in such areas.

2) Subsidence due to loading (e.g. large river system deltas), all
things equal, this results in a relative rise of sea level in
such areas. Subsidence due to groundwater depletion also has
local effects.

3) Thermal expansion due to heat content of the ocean. You've
calculated
this above. Note that the thermal content of the ocean changes
relatively slowly as the thermohaline circulation moves water
between colder and warmer regions. The thermohaline circulation
has a period of about 1600 years (for water to make a complete
cycle). The thermal input is via thermal diffusion between the
air and the water, so the rate is governed by the difference in
water and air temperatures. This also implies that more than the
top 50 feet of the ocean matters, since the warm water sinks at
the poles, moves equator-ward and upwells causing warming at all
levels to some extent.

4) Melting of land-bound ice (note that as floating ice (e.g. the
Arctic)
melts, sea level is not affected) such as Greenland, the
Antarctic plateau (but not the floating sea-ice) and continental
glaciers. I'll note here that southern hemisphere ice extent
hasn't changed much at all since 1979 (if anything, it has
increased), while the northern hemisphere icecap has thinned and
shrunk over the same time period (there is no satellite data
prior to 1979). There hasn't yet been much change to Greenland
(in fact, recent research has significantly lower estimates of
greenland ice loss).

5) Groundwater drawdown (since most of it ends up flowing to the
ocean
via runoff or precipitation). Note that this has been calculated
to be a significant portion of the sea level rise to date, with
different studies showing different levels based on different
assumptions as to the amount of geologic water that has been
withdrawn.

6) Currents caused by prevailing winds tend to cause surges in
certain
areas; tidal effects thus vary (some areas have larger
differences between low and high tides than others). If the
prevailing winds change due to thermal radiation/circulation
changes, then there will be changes in the tidal response in
various areas.

scott

Indeed. Note that perhaps total area of southern ice has not changed
that much, except for floating ice. But there are indications that at
least a number of antarctic glaciers have speeded up tremendously,
suggesting the transfer of volumes (not area) of ice into the ocean.
Implied is that this ice will melt and the water will raise the ocean
levels, eventually.

--
Best regards
Han
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