🚀 go-pugleaf

Being a geoscientist, I do not dispute that glaciers are melting and sea
levels are rising.  Much geologic evidence points to 70% of the continents
being covered by oceans as recently a 100K years ago.  We have almost no
continental landmass covered by the seas which is in direct conflict with
the geologic record. Transgressions and regressions of the seas are
prevalent throughout earth history.  Recent Pleistocene rocks in the
Sahara and Gobi deserts show deep wave-cut cliffs and beach deposits far
up on the hillsides.  Wave-cut terraces occur as much as 300 ft. above the
Great Salt Lake.  

Many scientists use the amount of water locked up or released by glaciers
to (at least partially) explain fluctuations in sea level.  There have
been repeated periods of continental and alpine glaciation and associated
changes in sea levels during earth's history.  Most scientists agree that
there are three basic controlling factors that can explain cyclical
glaciation.  These are: 1) astronomical control, 2) atmospheric control,
and 3) oceanic control.  They may act alone or in concert to control
glaciation.

1) Astronomical control was first proposed by Russian meteorologist, M.
Milankovitch and involves the amount of solar radiation received by the
northern hemisphere during a year.  The earth's axis is now inclined at
23.5 degrees to the plane of our orbit around the sun.  It is this
inclination that produces the seasons.  However, this inclination of the
axis varies from 21.5 to 24.5 degrees in a 40,000 year cycle.   A larger
inclination produces warmer summers and colder winters; a smaller
inclination produces warmer winters and cooler summers.  Also, the earth's
orbit is an ellipse of varying eccentricity.  This eccentricity varies in
a 92,000 year cycle. Presently, our orbit is at about maximum eccentricity
and summer occurs when the earth is farthest from the sun.  

Additionally, the earth wobbles like a top and the rotational poles point
in various directions in space. The North Pole now points almost directly
at the North Star but this has not always been the case.  This wobble
causes a precession of the equinoxes (s shift over time for when our
seasons will occur) and varies in a 21,000 year cycle.  When all of these
cycles are plotted in time there is fairly good correspondence between
these cycles and paleotemperatures based on oxygen isotopes. The predicted
cool periods in the cycles correspond well to the four major glacial
episodes.  These cycles suggest that we are coming off a cool climatic
period associated with the Pleistocene glaciation.  The minimum amount of
solar radiation based on these curves occurred about 19,000 years ago. 
Since then, these curves would predict more and more insolation and a
gradual warming trend.  This theory may explain why
continental glaciers have receded and sea levels have risen 150 ft. during
the last 11,000 years.

2) Atmospheric control relies primarily on variations in the carbon
dioxide content of the atmosphere to explain multiple periods of
glaciation.  An increase in CO2 through volcanism, forest fires or some
other carbon imbalance would result in warming global temperatures.  A
decrease in CO2 levels would lead to a cooling of the earth and possibly a
glacial ice age.  There is a good correlation between CO2 content in the
atmosphere and major periods of glaciation.  Most research efforts are
currently focused on this atmospheric control to explain the increase in
global temperatures and the rise of sea levels.  It is becoming
increasingly clear that CO2 from burning fossil fuels and the release of
other gases by man are probably accelerating this warming trend and the
associated sea level rise.  However, it is far from evident this is the
underlying cause of the rise in sea level.

3)  Oceanic control involves the freezing and thawing of the Arctic Ocean
to explain cyclic glaciation as observed in the rock record.  This theory
was first proposed by Maurice Ewing and William Donn.  They theorize that
as the ice caps and glaciers melt the ocean levels will rise. This leads
to the Arctic Ocean becoming slower and more difficult to freeze in
winter.  An ice-free Arctic Ocean will pump moisture into the atmosphere
creating clouds and snow.  As the snow accumulates in northern Canada and
Eurasia it builds into continental scale glaciers.  These continental
glaciers reflect solar energy back into space and the earth cools. When
the ice sheet has moved far enough south it becomes nourished by moist air
from the Atlantic and Gulf of Mexico so it is no longer dependent on the
Arctic for moisture.  At 40-50 degrees north latitude the rate
of advance would be balanced by the rate of melting and the ice sheet will
stop.

At the same time, ocean temperatures would drop because of the lowering of
global temperatures, lowering of sea levels (due glacial build-up) and
influx of meltwater.  These factors combined make less ocean moisture
available and at some point the Arctic Ocean freezes over entirely which
cuts off the northerly source of moisture.  It is this lack of an abundant
moisture supply that causes the glacial retreat.  As they retreat, they
expose the massive amounts of pulverized rock and this creates dust.  The
dust forms a nuclei for water vapor and we get clouds to help trap heat. 
The climate would begin to warm until the cycle would start over.  

A recent twist on the oceanic control of glaciation involve geothermal
gradients near ocean spreading centers where there is an upwelling of
convection currents from the mantle.  It is postulated that these areas of
high heat flow from the earth's core are responsible for El Nino and
warming of the oceans.  This could warm the oceans and provide an ice-free
Arctic Ocean.

With the complexities of these and many other glacial climate theories ...
it is no surprise that specialists from around the world debated the issue
without reaching a conclusion at the recent meeting sponsored by NSF in
Woods Hole, Mass.

Don Ince