- - - - - - - - - - - - - - - - - - - - - - - -
Greetings,
This Digest Contains:
* A forwarded report on Rising Sea Levels
* The Ice Age Chart - by me
* Humor
Regards, Donald
- - - - - - - - - - - - - - - - - - - - - - - -
------------ Forwarded Report ------------
Date: Fri, 05 May 2000 16:04:48 -0400
Subject: NEWS REPORT: Rising Sea Levels
From: "Stephan A. Schwartz" <saschwartz@earthlink.net>
Here is another report on the climatic change debate. Let me say, again,
this is a subject about which one would be well advised to be aware.
-- Stephan
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
SOURCE: Science News, Vol. 157, No. 9, February 26, 2000, p. 138.
Climate's Long-Lost Twin:
A warm spell in the distant past holds soggy clues to the future.
By R. Monastersky
Along the coast of Chile, this raised terrace was a beach 400,000 years ago.
(Luc Ortlieb)
Clinging to a cliff in the Bahamas, high above the pounding surf, geologist
Paul J. Hearty takes care to avoid any missteps as he surveys the craggy rock.
"These are 20-to-30-meter-high cliffs," he says. "I'm suspended by my
fingers and toenails, with the waves crashing below."
Though the threat of a fall keeps Hearty on edge, the real drama of this
spot lies exposed in the alternating stripes of stone running along the face
of the cliff. Thin red bands of fossilized soil separate massive white
sheets of limestone-strawberry icing spread between layers of coconut cake.
For a geologist reading this code, the bands recount a distant time when
Earth's climate displayed its wild side.
The thick limestone layers are ancient beach deposits, formed during warm
breaks between ice ages. In those cold times, dust from the Sahara laid down
thin red sheets. Hearty has come to the cliffs searching for a distinctive
limestone band from 400,000 years ago, a warm interlude known as stage 11.
Today, the former beach sits so far above the ocean that a fall from this
height could kill. Back then, however, the seas washed over it. For the
oceans to have swollen that much, significant portions of Earth's polar ice
must have melted, says Hearty, who works as a geologic consultant in
Honolulu. If such a melting were to happen today, breakers would crest over
much of the property in Miami, New York, and other cities near the sea.
For decades, coastal geologists such as Hearty have been finding scattered
hints of greatly elevated sea levels during stage 11. Their voices, however,
were drowned out by the majority of oceanographers, who viewed sea levels as
unremarkable at that time. Swept away by the opposition, Hearty and his
colleagues found themselves floating far from the main current of
scientific consensus.
In the past few years, though, new evidence has surfaced to shore up
support for this massive melting.
"The geological evidence for higher sea level during stage 11 is beginning
to mount up, so it's got to be given a lot of credibility," says Richard Z.
Poore, an oceanographer with the U.S. Geological Survey in Reston, Va. "I
think the evidence that sea level was significantly higher than today is
pretty good."
The stage 11 question is critical because scientists are starting to view
this time as a twin of our present climate. If we want to know what bobs
ahead in the future-if polar ice will melt and sea level will rise
catastrophically-this long-gone period could offer the clearest view.
The last ice age ended over 10,000 years ago, an apparent eternity to a
society fueled by drive-through restaurants, microwave popcorn, and E-mail.
To a geologist, however, today's warmth is just a blip. For much of the past
million years, Earth has shuddered through a series of ice ages, each
lasting close to 100,000 years. Punctuating these chills are relatively
brief interglacial periods like the current time.
In the 1950s, when oceanographers first discovered signs of this glacial
cycle recorded in deep-sea sediments, they named the various epochs going
backward, starting with the present interglacial as stage 1. Four separate
glacial periods separate modern times from the epoch known as stage 11.
During ice ages, glaciers more than a kilometer high covered large swaths of
North America and Europe. These temporary ice sheets drew so much water from
the oceans that sea level dropped by 120 meters in the most frigid
intervals. When climate warmed during interglacials, the North American and
European ice sheets melted, sending sea levels back up to a height on par
with today's. At least, so goes the standard scientific story.
The new evidence of elevated sea levels is rewriting that well-worn tale.
Along the cliff face on the island of Eleuthera, in the Bahamas, Hearty has
found a distinctive herringbone pattern in the limestone. This arrangement
of ridges would be familiar to any beachgoer. It's made up of fossilized
relicts of the sand ripples that swimmers can feel beneath their feet as
they wade out from shore. The pattern means that these rocks, now 20 m above
the sea, were once below the low-tide mark, Hearty and his colleagues
reported in the April 1999 Geology.
His team has found similar evidence in Bermuda and, more recently, on the
Hawaiian island of Oahu, he announced last December at a meeting of the
American Geophysical Union (AGU) in San Francisco.
The deposits on Oahu now exist 26 to 30 m above sea level, significantly
higher than the fossilized deposits in Bermuda and the Bahamas. The
difference, says Hearty, is that the two Atlantic sites have remained
geologically stable over the millennia, whereas the Oahu site has risen 8 m
in 400,000 years, according to his calculations.
The problem of shifting coastlines complicates the job of geologists who are
trying to unravel exactly how high the seas crested in stage 11. As the land
rises or sinks, it skews the evidence of past sea levels.
Some scientists question whether even Bermuda and the Bahamas have provided
a true record. "Given what we know about plate tectonics, it's very unlikely
that anywhere on the coast has been stable for 400,000 years," says David Q.
Bowen of Cardiff University in Wales.
At the recent meeting, Bowen reported on his studies of ancient beach
deposits around southern Britain that now perch between 20 and 43 m above
sea level. Bowen has estimated the uplift rate by looking for evidence of
sands laid down during the last interglacial. Because this warm period
happened relatively recently, about 120,000 years ago, scientists could
independently determine its sea level.
Measuring against the deposits, Bowen calculated how quickly these sites
have risen. This rate indicates that stage 11 sea levels reached around 15 m
above the modern value. Though lower than Hearty's figures, Bowen's
calculations still point to a substantial melting of polar ice at the time.
More support comes from sites in northern Alaska that preserve evidence of a
13-m rise in sea level, reports Julie Brigham-Grette of the University of
Massachusetts at Amherst. "A lot of us who work on stage 11 have realized
that we really have compelling evidence on a global basis, if we put it
together," she says.
The face of the globe would have looked far more swarthy during stage 11 if
sea levels then surpassed the modern mark by 13 m or more.
Today's porcelain-white island of Greenland would have lost its icy coating
and, as vegetation sprouted across the rocky surface, turned a darker shade
more true to its name. The melting of this northern ice could account for 6
m of the sea level shift.
To find the rest, one must head south, says Reed P. Scherer, a researcher at
Northern Illinois University in Dekalb who studies the climate history of
Antarctica. The most probable suspect in this case is West Antarctica-the
half of the continent that reaches toward South America.
Ice on the other side of Antarctica rests high and dry on rock mostly above
sea level, making it far more stable than the West Antarctic ice sheet,
whose base lies below sea level. Some scientists have theorized that the
arrangement in West Antarctica makes that region prone to collapsing when
climate warms because the swelling oceans would undermine its base.
The theory itself lacked much support until Scherer started studying gravel
that a drill team had collected from beneath the West Antarctic ice sheet.
The marine sediments contained the shells of one-celled algae with a
distinctive shape.
>From records elsewhere, Scherer knew that the algal species found under West
Antarctica had appeared only within the past 750,000 years. Scientists once
thought that the West Antarctic ice had been stable for more than 6 million
years, but Scherer's evidence revealed its erratic nature. The presence of
relatively modern algae indicates that much or all of West Antarctica must
have melted sometime within the past million years, leaving open ocean in
its place.
Head for the hills: A 10-meter rise in sea level (red) would flood 63
million people along the East and Gulf Coasts of the United States. (USGS)
While he cannot pinpoint when West Antarctica collapsed, Scherer says that
"stage 11 is the most likely candidate."
Melting the western side of the continent, however, would only account for
another 6 m of sea level rise. With Greenland's contribution of 6 m, it
would be enough to satisfy the lower estimates but not the full 20 m. To
reach that upper figure, about 10 percent of the ice currently in East
Antarctica would have had to disintegrate as well.
With so much freshwater flushing into the oceans at that time, the thawing
of polar ice should have left its signature on the seawater's chemistry.
Oceanographers have searched for this imprint, but their results generally
pour cold water on the idea of significant melting.
"Our evidence does not strongly support a much higher sea level," says Jerry
F. McManus of the Woods Hole (Mass.) Oceanographic Institution.
To track ancient sea levels, McManus and others rely on the split nature of
oxygen atoms in the ocean. When water evaporates from the seas, it
preferentially carries away the lighter isotope of oxygen, which can become
trapped in snow and glaciers. The seawater left behind shows an increased
proportion of the heavier isotope. Tiny marine organisms preserve a record
of the shift in their shells, which eventually fall to the seafloor.
If during stage 11, melting ice pumped up ocean levels by 20 m, it should
have lowered the ratio of heavy to light oxygen in these shells, says
McManus. The records from the North Atlantic, though, show no dramatic
events at the time. The simplest explanation is that sea levels remained
near today's value, he says.
McManus admits, however, that something else may have happened at the time
to hide the evidence of melting. If the North Atlantic cooled slightly, the
temperature shift would have pushed the oxygen-isotope ratio in the opposite
direction, counterbalancing the signal from polar melting.
That's what Poore thinks happened. He has recently collected sediment cores
from the Cariaco Basin off Venezuela, where the stage 11 story reads
differently from the way it does in the North Atlantic. The shells of
single-celled animals that lived in the basin's waters during stage 11
contain significantly more of the lighter isotope than is seen in modern
shells.
"The easiest way to explain this is to say that sea level was higher and
global ice volume was less than today," says Poore.
As a species, people have tended to congregate close to the ocean, so a
repeat of stage 11 would send much of the world scurrying for higher ground.
A full quarter of the current U.S. population would find itself underwater
if sea levels were to rise by 10 m, calculate Poore and his colleagues.
Scientists disagree on whether coastal residents should worry about the
long-term value of their property. The present interglacial has lasted
10,000 years, only about a third of the length of stage 11. So, melting of
the polar ice could lie many millennia in the future.
On the other hand, global temperatures are rising rapidly, and greenhouse
gases threaten to accelerate the warming in the next few decades.
Poore takes a conservative approach. "There's nothing to worry about next
week. But it's wrong to just think that it's a problem 500, 600, or 700
years in the future. I think it could be problem much sooner than that."
Hearty agrees, saying, "As the greenhouse effect tends to increase the
temperature of the Earth over the next 50 to 100 years, we can probably
expect that some of the Antarctic ice will melt and destabilize." He notes
that small blocks of Antarctic ice have already started to collapse from
rising temperatures.
Bowen, who considers himself a skeptic regarding greenhouse warming, says
that human activity has no bearing on the issue of polar melting. "My view
is straightforward: The longer an interglacial lasts, the higher the sea
level is eventually going to be," he says.
"It's like building a big snowman in the garden. If it's a big enough
snowman, it will last long after the weather has warmed up. It will keep
trickling away slowly," he explains. "For the present interglacial, sea
level is going to trickle upwards until the climate switches and we start
descending into the next ice age."
Scientists once thought that polar ice would have little trouble lasting
until the next big freeze. The current interglacial is nearing its
conclusion, according to conventional wisdom. Once the world made it past a
few centuries' worth of greenhouse warming, the climate would start getting
cold again.
This conclusion rested on the assumption that the current interglacial would
persist only about 10,000 years, the length of the last interglacial, which
occurred 120,000 years ago. Recent studies, however, have demonstrated that
the last interglacial does not make a good model for understanding the
present. Instead, stage 11 has emerged as the better example.
Scientists base the comparison on features of Earth's orbit. Every 400,000
years, the shape of the orbit varies from a squashed circle to a more nearly
perfect one. This shape alters the amount of summer sunlight hitting the
Northern Hemisphere-the factor believed to push Earth into and out of ice
ages. Modern times resemble stage 11 in that the orbit is nearly circular,
which tends to dampen the climatic influences of other orbital factors, says
André L. Berger of the Catholic University of Louvain in Belgium, who
presented his findings at the recent AGU meeting.
Berger uses Earth's orbital variations to calculate how insolation-the
amount of sunlight hitting the planet-changes with time. In simulations
using a computerized climate model, Berger and his colleagues found that the
orbital effects would keep Earth out of an ice age for 30,000 years,
producing an exceptionally long interglacial matched only by stage 11.
For the next few thousand years, he says, the sunlight variations will be
rather weak. "The insolation is not going to vary that much. It will almost
remain constant. That means that the other factors are going to play a very
important role. Among those other factors are greenhouse gases."
This quirk in the timing of Earth's orbital wiggles has given greenhouse
gases unusual potency in terms of changing climate, he says. Even just a few
thousand years ago, the shape of the orbit was different enough that the
astronomical forces would have exerted a controlling influence on climate,
leaving less room for carbon dioxide and other gases to exert power.
The result is the climatic equivalent of Murphy's law: Humans have started
exploiting fossil fuels and altering Earth's atmosphere at precisely the
moment when greenhouse gases could do the most damage to climate.
If societies had bloomed and used up all the coal, oil, and natural gas
several millennia earlier, greenhouse warming might have come and gone
quietly, without any possibility that melting polar ice caps would
eventually flood what people have erected.
- - - - - - - - - - - - - end - - - - - - - - - - - - -
Greetings,
I have constructed the following Ice Age chart based on the numbers
given in the above report. The years are approximate, but the chart does
give us a perspective. The Ice Age seems to be the norm, the stable
condition of our planet and the warm periods are the exceptions.
Donald Davison
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
T H E I C E A G E C H A R T
YEAR 470,000 BC - Start of 30,000 year Interglacial warm period.
[+10K]
[+10K]
[+10K] 440,000 BC - Start of 100,000 year Ice Age
[+10K] +---------------------------------------+
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] | I C E A G E |
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] +---------------------------------------+
[+10K] 340,000 BC - Start of 10,000 year Intergacial warm period.
[+10K] 330,000 BC - Start of 100,000 year Ice Age.
[+10K] +---------------------------------------+
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] | I C E A G E |
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] +---------------------------------------+
[+10K] 230,000 BC - Start of 10,000 year Interglacial warm period.
[+10K] 220,000 BC - Start of 100,000 year Ice Age.
[+10K] +---------------------------------------+
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] | I C E A G E |
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] +---------------------------------------+
[+10K] 120,000 BC - Start of 10,000 year Interglacial warm period.
[+10K] 110,000 BC - Start of 100,000 year Ice Age.
[+10K] +---------------------------------------+
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] | I C E A G E |
[+10K] | |
[+10K] | |
[+10K] | |
[+10K] +---------------------------------------+
[+10K] 10,000 BC - Start of 30,000 year Interglacial warm period.
[+12K] 2,000 AD - Today we are 12,000 years into the warm period.
[+03K] 5,000 AD - Peak high temperature under normal conditions.
[+15K] 20,000 AD - Expected start of next 100,000 year Ice Age.
[+10K]
[+10K]
[+10K]
[+10K]
[+10K] N E X T I C E A G E
[+10K] (maybe not)
[+10K]
[+10K]
[+10K]
[+10K] 120,000 AD - Start of 10,000 year Interglacial warm period.
I have listed the year 5,000 AD as the year of the next peak high
temperature under normal conditions, but we do not have normal conditions.
Because mankind has been dumping CO2 into the air, we can expect to reach
the temperature of that peak much sooner and then we can expect to have a
much higher peak later on. Hopefully this much higher peak will occur at a
value less than the point of No Return. If not, there will be no more ice
ages. We will be on our way to a Venus Greenhouse. Donald
- - - - - - - - - - - - - - - - - - - - - -
Humor:
On an Electrician's truck: "Let us remove your shorts."
Outside a Radiator Repair Shop: "Best place in town to take
a leak."
In a Non-smoking area: "If we see you smoking we will assume
you are on fire and take appropriate action."
On Maternity Room door: "Push, Push, Push."
At an Optometrist's Office: "If you don't see what you're
looking for, you've come to the right place."
At a Car Dealership: "The best way to get back on your
feet - miss a car payment."
Outside a Muffler Shop: "No appointment necessary. We'll
hear you coming."
Outside a Hotel: "Help! We need inn-experienced people."
At an Auto Body Shop: "May we have the next dents?"
In a Dry Cleaner's Emporium: "Drop your pants here."
In a Veterinarian's waiting room: "Be back in 5 minutes.
Sit! Stay!"
On a Music Teacher's door: "Out Chopin."
At the Electric Company: "We would be delighted if you send
in your bill. However, if you don't, you will be."
On the side of a Garbage Truck: "We've got what it takes to
take what you've got."
On the door of a Computer Store: "Out for a quick byte."
In a Restaurant window: "Don't stand there and be hungry,
come in and get fed up."
Inside a Bowling Alley: "Please be quiet. We need to hear
a pin drop."
In the front yard of a Funeral Home: "Drive carefully, we'll
wait."
- - - - - - - - - - - - - - - - - - - - - - -
Humor to lighten up
Morris was removing some engine valves from a car on the lift
when he spotted the famous heart surgeon Dr. Michael DeBakey, who
was standing off to the side, waiting for the service manager.
Morris, somewhat of a loud mouth, shouted across the garage, "Hey
DeBakey . . . . Is dat you? Come over here a minute."
The famous surgeon, a bit surprised, walked over to where Morris
was working on a car.
Morris in a loud voice, so all could hear, said argumentatively, "So
Mr. fancy doctor, look at this work. I also take valves out,
grind 'em, put in new parts, and when I finish this baby will
purr like a kitten. So how come you get the big bucks, when you
and me are doing basically the same work?"
DeBakey, very embarrassed, said softly to
Morris,..."Try doing your work with the engine running."
- - - - - - - - - - - - - - - - - - - - - - - - -
To Unsubscribe: Email majordomo@cals.ncsu.edu with the command
"unsubscribe sanet-mg". If you receive the digest format, use the command
"unsubscribe sanet-mg-digest".
To Subscribe to Digest: Email majordomo@cals.ncsu.edu with the command
"subscribe sanet-mg-digest".
All messages to sanet-mg are archived at:
http://www.sare.org/san/htdocs/hypermail
This archive was generated by hypermail 2b29 : Mon Jul 03 2000 - 12:00:35 EDT