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Will global warming lead to an 'ice age'

Persistent myths are circulating that suggest that disruption of the Atlantic conveyer belt leads to an 'ice age'.
In order for a true ice age to occur, it is required that temperatures in the summer drop to such low levels that it effectively remains winter all year round. Snow that falls in the winter therefore never does melt, but rather continues to accumulate, and the end result is an 'ice age', and the creation of ice sheets as much as two miles thick, the result of annual accumulation of snow cover over many centuries.

A few hundred years ago a not very well understood climate event took place, typically referred to by the misnomer 'the little ice age.' Because this climate event has been misnamed as 'an ice age', this has led to some rampant speculation on the internet that 'global warming causes an ice age.' This is not true.

According to the Ocean and Climate Change Institute
 link to www.whoi.edu
"The Little Ice Age... was a five-hundred-year-long period of cold conditions affecting Europe and eastern North America. Contrary to what the name suggests, it did not involve ice-covered continents, as in a "real" ice age. But it did cause enough cooling to disrupt human activities...(It did) cause severe winters on both sides of the Atlantic."
They also point that "many of the models used to study changes in ocean circulation have inadequate representations of ocean processes. The models may also be less sensitive to salinity perturbations than the actual ocean is. As a result, we are not yet in a position to predict these types of ocean circulation changes." However they also point out that a study of ocean sediments does suggest that "The climate history of the earth shows that adding freshwater to the North Atlantic disrupts the ocean circulation in ways that cause regional cooling and alter patterns of rainfall and drought."

Therefore the possibility exists that 'Global Warming', by introducing fresh water into the North Atlantic, could affect the Atlantic Conveyer Belt, an ocean current which transports warm tropical water to the western coast of Europe. The water then sinks to the depths of the ocean as it cools, while the heat is released into the atmosphere, and it is this released heat that is responsible for the moderate winters in Europe as compared to the harsher winters in North America. Therefore, there is a possibility that Global Warming could temporarily create the conditions for much harsher winters, but not an 'ice age'. This is a myth being spread around on the internet caused by the misnaming of the 'little ice age' several hundred years ago, which was not an actual 'ice age' (with glaciers and ice sheets covering continents) but rather a time of particularly harsh winter climates. When summer came the snow melted, and there was no accumulation of vast ice sheets.

Ice Ages follow a pattern which is established by variations in the patterns of the Earth's Orbit around the sun and variations in the earth's tilt and rotation. The Earth does not follow a perfectly circular orbit, but rather it follows an eccentric elliptical orbit, with a cycle of one hundred thousand years. The amount of sun light reaching the earth varies depending on how extreme the distance of the earth is at the maximum of the elliptic as well as the variation of distance during each season. The earth also wobbles as it spins, up to 23.5 degrees, a cycle which takes 41,000 years. This wobble also causes the position of the earth in its elliptical orbit to change, a phenemona known as the precession of equinoxes, which follows a cycle of 23,000 years.

Ice Ages occur when all three of these factors are in favorable alignment resulting in the least amount of summer warmth in the Northern hemisphere when summer occurs at the farthest point in the Earth's elliptical orbit. Summer temperatures therefore plunge to winter like conditions, and snow accumulates from year to year rather than melting. Similarly, the ice age ends when the process is the opposite, resulting in increased summer heat, and summers which take place at the closest point in the elliptical orbit.

Not enough information is available to climate modellers to give a firm prediction of whether or not a period of cold winters will result from global warming processes, which explains why they are always found to be lobbying bodies such as Congress for more research grants. The atmosphere is much better understood than the ocean. You might encounter emphatic statements out on the internet that suggest that it is a definite certainty that there will be another ice age caused by global warming, and this once again is a myth based upon a misunderstanding of both the state of oceanic climate science (it is underfunded, and thus these statements are just the expression of one possibility, typically, you might notice, combined with an appeal for more funding to increase our knowledge, which is then misinterpreted as being statements of exact fact...to make matters worse the term 'little ice age' is a misnomer, and thus once again causes all that speculation out on the internet about coming glaciation and so on, when the worst people could expect would be a particularly nasty winter, since it is not at all probable that summers will become winter due to global warming, thus leading to an ice age, since the process of a true ice age is controlled by rotation, spin, and orbital variations of the earth, and is not driven by any of the factors influenced by global warming processes.

Some links
Signs of Rapid Arctic warming since 2000
Siberian permafrost is melting, leading to the potential release of up to 70 billion tons of methane, a greenhouse gas 20 times more powerful than carbon dioxide. The last time this happened, during the Thermal Maximum, much of the United States was plunged under water (see the graphics on the linked page), and became part of the ocean, and this scenario is much more plausible than the misunderstood scenario being spread around on the internet which suggests that the United States will buried under glaciers due global warming.

Arctic ice cap at record low
The melting of Siberia has been taking place over the last three or four years, around the same time that the arctic ice cap has been shrinking at an accelerated rate, leading scientists to lower their estimates of an ice free arctic from the year 2100 to the year 2060 given the accelerated rate of melting taking place since 2000. This can be graphically seen on the video linked to on the page below, where the most rapid shrinkage takes place right near the very end of the video.

other climate stories...

Good debunk 10.Oct.2005 11:30

Red neck

I love it when people slap stupidity in the face...need so much more of that.
What's going to cause another ice age is peak oil. American's are going to get a little ice age this winter as prices for home heating oil go through the roof...shouldn't have been heating the great outdoors all these years, huh?

Well done! Thankyou. 10.Oct.2005 14:11

A. Reader

I am downloading your article, so I will have it available for the next idiot that goes off on me about the coming ice age!

That's right 10.Oct.2005 17:10


Technically, the "little ice age" was not an ice age. It was a short period of glaciation which means that the climate snapped out of the temperate condition that we have been experiencing for the past several centuries.

That said, when it happens again, the people who will be experiencing global famine because of the shortened growing season will not give a hoot what you label it!

ummm... 10.Oct.2005 18:21

this thing here

i do not doubt for second that there may very well have been a "little ice age", or more accurately a period of below normal temperatures that did NOT result in an ice age. this is perfectly reasonable to me. it's probably happened countless times in the history of the earth's climate.

but how does this explicity disprove the possibility of another ice age? there is nothing in this arcticle which explains why a massive infusion of cold fresh water, leading to a shutdown of the so called atlantic conveyor belt, would NOT result in an ice age. show me the science.

Great article 10.Oct.2005 18:36

eva destruction

This is why IPCC predicts warming, not cooling of the planet.

this "debunking" is not scientifically well informed 10.Oct.2005 20:54


I'm afraid that while Brent Herbert has a lot of his facts right, specifically about the astronomical forcing of the roughly 100,000 year long glacial cycle (which has dominated Eart's climate for the last few million years) his overall conclusion is actually not entirely clear. The global climate system is horrendously nonlinear, meaning not only that relatively small changes can have very large effects, but that the effects can be quite unexpected. There is now a wealth of paleoclimate data from deep ice cores from the Antarctic and Greenland ice sheets showing that global climate can in fact go through large changes on the time scale of only decades. For example, after the end of the last major glaciation about 12 thousand years ago, the earth warmed up, but the ice sheets did not instantaneously decay. The warming was interrupted by an event known in geological circles as the Younger Dryas, when Earth cooled significantly for about 1000 years before warming again. Again, the onset and end of the Younger Dryas was very rapid. There is a huge amount of data about this event; see for example


A nice summary of some of the issues around possible instability of North Atlantic circulation (which Herbert alluded to) is in an accompanying item:


There is a glaciologist/paleoclimatologist (Prof. Hulbe) in the Dept. of Geology at Portland State University who could comment very thoroughly about this issue.

the younger dryas 11.Oct.2005 01:40


The younger dryas occured sometime around 12,000 years ago, when the large ice sheets of the last ice age halted the melting process for about 1,000 years, with the change going into the period and coming out of the period taking place in the span of around a decade, according to ice core samples, which demonstrates how the climate responds in a non-linear way. However comparisons made between the younger dryas and today and not really applicable, since the world was still covered by massive ice sheets at that time, a condition which does not exist today, making some kind of direct comparison between that phenomena and today's climate unreasonable...

according to what I have read, what is believed to have happened is that the Laurentian ice sheet broke apart, much like the Ward Hunt Ice sheet on Ellesmere Island broke apart two years ago, and this break up allowed a trapped Lake of cold fresh water to suddenly flood out of the center of the ice sheet, carving the St Laurence river system in the process (hence the name) and introducing large amounts of fresh water in the North Atlantic at the same time...

As much as fifty percent of the winter heat in places like Europe of the East Coast of the United States comes not from solar radiation but rather from heat released by the Atlantic Conveyer Belt, so the disruption caused to the ocean currents by this event then caused sufficient loss of warming from the tropics to halt the deglaciation...but remember, this was a period of deglaciation to begin with, and so trying to make some kind of comparison between the Younger Dryas and the modern world is like comparing apples and oranges...

One of the most significant variables today would probably be the billions of tons of methane which could be in the process of being released into the atmosphere by processes such as the now ongoing melting of Siberia, with a similar process seeming to in process in the Tundra areas of North America as well...the last time such large amounts of methane were released into the atmosphere all at once took place during the Thermal Maximum, about 55 million years agom and resulted in rapid global warming...this would be what you would expect when you wrap the earth in a blanket...not glaciation, or global cooling, but rather global warming...

The graph, from IPCC site shows the increase in methane in the atmosphere which rises sharply over the last century and a half...as you can see by the graphic of a farm with silos and a cow in the bottom right corner, this rise in methane is attributed to large scale livestock production...however even this sharp rise in methane levels cannot compare to the amount of methane that could be released by the melting of the permafrost in the frozen bogs of the high north. For comparison purposes, the United States releases about 6 million tons of methane into the atmosphere from livestock operations (mainly cattle) each year, while globally total human related methane release totals 30 million tons. Just the melting of western Siberia has the potential to release up to an estimated 70 billion tons of methane, which is on a scale of about 2,000 times more methane than the total annual anthropogenic forcing introduced currently by human processes. Such a large release of methane naturally then invalidates the conventional climate models which are based on moderate releases of greenhouse gases and predict relatively smooth and linear changes, and such moderate impacts as 'no sea ice in the arctic by 2100' when what we could actually be seeing is rapid climate, and no ice in the polar regions at all, and all this even before 2100.

of course all this is 'alarmist', but given how the 'moderate' scenarios do not seem to inspire people to take matters all that seriously, maybe a little bit of alarmist rhetoric is called for, especially when recent events would suggest that what is 'alarmist; might actually be what is realistic, while what is 'moderate' is actually dangerously over optimistic.

The IPCC methane graphic is found here
and links to other IPCC graphics are found here
Rise in Methane
Rise in Methane

Re: Will Global Warming Lead To An "Ice Age?" 11.Oct.2005 08:33


While this article discusses one possiblility, it does not consider others. If the ocean currents, such as the Gulf Stream, are slowed down because of melting glaciers and fresh water pouring into the oceans, the possibility exists that the currents will take a different course entirely. Furthermore temperatures in the upper atmosphere are supposedly dropping. This is due to the fact that more cold is being held up by warming ocean currents.

Why might the currents be warming more? Possibly due to the same reasons that hurricanes are gaining in intensity. Tropical waters are heating up due to the greenhouse effect and the Gulf Stream is pumping up even higher than normal water and thus air temperatures into the northern regions. Should such streams suddenly stop flowing, extremely cold upper atmospheric temperatures, long held at bay, would drop down quite suddenly. This could create a series of devestating supperstorms and we could easily go into a new, long lasting ice age.

This is another theory that is floating around. It's important to remember that every ice age was preceeded by a period of global warming; and look what happened - sometimes very suddenly.

Realistically, there is no telling where our tampering with the atmosphere can lead. But it certainly would seem to make sense that we excercise caution and care when dealing with our life support systems, rather than the absolute carelessness which is so popular today.

cold air 11.Oct.2005 10:14


actually the upper atmosphere is said to be colder, not because of the ocean currents, but rather because of Green house gases...more heat stays trapped near the earth and thus does not bounce back out to space as infra red radiation. Now radiation coming into the earth does not heat the upper atmosphere as much, since it comes in mostly in the form of light energy, and the gases in the upper atmosphere are not as sensitive to this energy, and more sensitive to infra red (or radiated heat energy) and it is this infrared which is trapped by greenhouse gases, resulting in a warmer earth, and a colder upper atmosphere.

Now even if some cold air up above 'dropped down' this could not cause an ice age, since ice ages are not caused by something like that...air is one of the most rapid conductors of heat as you can tell by holding your hand over the burner on a stove, the heat transfers through the air immediately...but put a pot of water on the stove and you will be waiting a while for the heat to transfer...so even if it were possible for 'cold upper air' to fall down to earth, it would not cause an ice age, but would quickly heat,...as

super-glacial melt tsunamis destroying Atlantic conveyors means unpredictable 12.Oct.2005 01:49


Though I do think Brent has summarized a great many of the main "large" variables and knows what he's talking about in terms of their general additive or substrative effects on each other, it is self-contradictory to say that on the one hand no one knows, and then to go on the other hand right into stating a three-variable theory that claims to predict all ice ages forever and always, Amen. No one knows...except Brent, I guess? Critique of that done. I do like Brent's posts though.

First, another variable I would throw into the mix is sudden nearly unpreditable traumatic bursts of incredibly cold water into the oceans--or their lack, for a while--which could effect large scale climate issues within Brent's model. These, however, would be hardly predictable issues since they involve sudden bursts of huge towering floods getting stored up as meltwater within or on super-glaciers. When such meltwater tends to break out, it snowballs.

Over these 1000 mile glaciers, you feasibly would get roaring walls of cold tidal waves zooming across the glaciers--picking up speed, near freezing water sitting in ice calderas, more broken ice, snow, slush, carried rocks, etc. All this is increasingly moved across glacial surfaces faster and faster--until it dumps itself quite violently onto land or into seas. This would cause horrendous land floods burying all life at near freezing water temperatures, or the aftereffects of global tidal waves which cause the same elsewhere.

Any evidence for that? First, In the glacial areas of the Wisconsin ice age for instance, you get scientists currently saying things like the Wisconsin Dells--a massively eroded area once deep under the edge of the Wisconsin-Wurm period super-glacier--has many rocky crevasses that are fantastically carved. Many of these crevasses are 30-40 feet deep. It is claimed that they were eroded quickly, within several weeks. That a pretty blistering flood condition. Another bit of evidence is how they found the perfectly preserved mammoths in Siberia typically encased standing up and surrounded by a bunch of frozen flood condition bits of trees, grasses, dirt, ice, rocks, snow, etc. They were immediately buried in something traumatic, by something that left no where to escape. Then they were flash frozen surrounded and buried in hundreds of feet of slush and ice.

Third, think of this super-glacial tidal wave sliding over hundreds of miles and then hitting the ocean and creating global tsumamis. What about all that push of cold water? I bet it would disrupt oceanic conveyors.

None of all this would be seriuosly predictable, at least as easy as those three variables above...

besids such an "injection" of millions of gallons of cold water into certain areas certainly would affect climate conveyors in the ocean. Just a thought. That as well would be pretty quick, though hardly durable. That may explain a lot of the reputedly incredibly rapid climate variations over the last ice age melddown period: the oceans got injected with hundreds of cubic miles of water on an irregular size, basis, and location.

On a separate issue: a little natural experiement about how durable warm weather might cause an ice age by disrupting the conveyor is staring us right in the face. Instead of simply talking about the "little ice age", go back several hundred years before. Is this comparable to where we are now?

I note that that right before the (agreeed misnamed) "little ice age" conditions, Europe was incredibly hot and getting hotter. You had wine grapes growing in England for quite a while beforehand--for the first time. I've never seen anyone talk about how this superwarm period occurred before the "little ice age" or why this might be related to what followed. I would hypothesize that somewhere the Atlantic Conveyor may have been shut off by unseasonably and durable warm weather in Greenland. After all, this was the period in which the Vikings were more or less colonizing the area, with ruminant animals, no less, and agriculture. Maybe Greenland was indeed green after all. Perhaps this incredibly hot period right before the 'little ice age' had set off a conveyor diruption in the Atlantic, leading, voila, to the 'little ice age' afterwards.

Here's something to blow your mind on these issues. A book that explores such climate variation issues and potential ramifications of sudden and mostly unpreditable changes like this:

Underworld : The Mysterious Origins of Civilization
by Graham Hancock (Hardcover - October 15, 2002)
 link to www.amazon.com

pertinent new scientific article 14.Oct.2005 10:17

anon geophysnerd@yahoo.com

Here is the text of an article in the earth-science literature that is intended for a general earth-science readership and ought to be understandable by most readers of this site. Sorry about the funky formatting and lack of figures. Readers who would like to receive a PDF version with figures can write to me at the indicated address.

Eos (Transactions, American Geophysical Union), October 4, 2005

Meltwater drainage from glacial Lake Agassiz
has been implicated for nearly 15 years as
a trigger for thermohaline circulation changes
producing the abrupt cold period known as
the Younger Dryas. On the basis of initial fi eld
reconnaissance to the lake's proposed outlets,
regional geomorphic mapping, and preliminary
chronological data, an alternative hypothesis
may be warranted.
Should ongoing data collection continue
to support preliminary results, it could be
concluded that Lake Agassiz did not fl ood
catastrophically into the Lake Superior basin
preceding the Younger Dryas (Figure 1).All
preliminary findings imply a retreating ice
sheet margin approximately 1000 years younger
than previously thought, which would have
blocked key meltwater corridors at the start of
the Younger Dryas.
If Lake Agassiz meltwater passing into the
North Atlantic is not the trigger for the Younger
Dryas, then perhaps there were different
sources of water or triggers.At this point, it
seems prudent to carefully examine the role
of glacial Lake Agassiz in any abrupt climate
change scenario.
The current paradigm for driving abrupt
climate change is the modification of thermohaline
circulation by the addition of external
freshwater to the North Atlantic Ocean. Numerous
modeling experiments have demonstrated
the extreme sensitivity of this system,
and attributing the source of that freshwater to
glacial Lake Agassiz has evolved with numerous
In the mid-1970s, Kennett and Shackleton
[1975] noted that the isotopic composition of
seawater in the Gulf of Mexico fl uctuated substantially
during deglacial time, and they attributed
the fluctuation to changing sources of
meltwater from the Laurentide Ice Sheet.Approximately
coeval with the isotope changes,
the Laurentide Ice Sheet retreated northward
into an isostatically depressed basin behind
the subcontinental drainage divide. Researchers
in the Great Lakes reconstructed lake-level
history, and they recognized variations in meltwater
routing either through the Mississippi
River to the Gulf of Mexico or through the St.
Lawrence River to the North Atlantic (Figure 1).
By the late 1980s, Broecker et al. [1989] had
honed the concept of a freshwater trigger
upsetting thermohaline circulation, and modeling
experiments defined the necessary meltwater
fluxes.The climate connection to glacial
Lake Agassiz arose because organic sediments
(10,960-9900 radiocarbon years [14C] B.P.) deposited
between two sequences of deepwater
clays would require a major drop in lake level,
i.e. a meltwater releasing event coeval with the
Younger Dryas.
Subsequently,Teller and colleagues [e.g.,
Teller and Leverington, 2004] employed
rebound models (delayed glacio-isostatic uplift
of the Earth's crust from ice-sheet loading
following deglaciation), lake-level histories,
and ice-retreat patterns to calculate meltwater
volumes reaching the North Atlantic via an
eastern route.These calculations were compatible
with modeling estimates needed to affect
ocean circulation.Thus, a terrestrial meltwater
drainage reconstruction for triggering the
Younger Dryas existed that was compatible
with ocean records.
Two Preliminary Trips
An initial aerial survey on 4-7 May 2003 of
areas north and west of Thunder Bay, Ontario,
referred to as the eastern outlets (Figure 2),
was followed by a second survey on 20-22
September 2003 north and east of Fort McMurray,
Alberta, along the Clearwater River.This
area is referred to as the northwestern outlet
(Figure 3). Boulders from moraine crests and
flood channels were collected in each area
for cosmic ray exposure dating.The results of
these surveys, and dates obtained, have directed
4 OCTOBER 2005
PAGES 365-373
Eos, Vol. 86, No. 40, 4 October 2005
PAGES 365, 372
Testing the Lake Agassiz Meltwater
Trigger for the Younger Dryas
Fig. 1. Digital elevation model of central North America showing the southern, eastern, and northwestern
outlets of Lake Agassiz.
Eos, Vol. 86, No. 40, 4 October 2005
further ongoing research activities.
In the Thunder Bay region, channels and dry
waterfalls in bedrock west and south (Ouimet
Canyon) of Lake Nipigon (Figure 2) were
examined, and they were considered by all
researchers as unconnected to discharge
coeval with the onset of the Younger Dryas.
Possible older outlets had been proposed
west, rather than north, of Thunder Bay, but
neither maps nor aerial survey revealed any
large continuous channels, dry waterfalls, or
spillways cut into bedrock, as is the case west
of Lake Nipigon or in the southern outlet of
Lake Agassiz.This was surprising, given the
proposed catastrophic nature of the fl ood necessary
to trigger a climate change.Alternatively,
the resistant bedrock of the Canadian Shield
prevented formation of a well-developed spillway,
resulting in non-catastrophic fl ow instead.
In contrast to the uncertain fl ood routing
west of Thunder Bay, the Clearwater spillway
(Figure 3) served as a route for meltwater
flows.The geomorphic evidence is stunning:
a wide, linear channel with numerous feeder
channels at its eastern end, and a large delta
at its downstream end. Catastrophic fl ood
deposits contain wood giving a maximum age
of 9860 ± 230 14C years B. P. [ Fisher et al., 2002].
Strandlines (water-plane indicators such as
beaches, spits, or escarpments) near the head
of this system are discontinuous and are covered
by boreal forest, with the only known
Agassiz strandline projecting to the base of the
spillway. Evidence that Lake Agassiz existed at the
head of the spillway is based on the distribution
of scattered high-elevation strandlines, lacustrine
sediment, and radiocarbon age-dated
fl ood gravels.
Given the importance of unraveling Lake
Agassiz's drainage history as a trigger for
abrupt climate change, and given that the
nature of the field evidence for Younger Dryasaged
drainage at either the eastern or northwestern
outlets is ambiguous, it was decided
to construct and apply a chronological test.
Did the ice sheet margin, either at Thunder
Bay or Fort McMurray, withdraw enough to
allow passage of meltwater at the start of the
Younger Dryas? An affirmative response allows,
but does not prove, an Agassiz meltwater
trigger; a negative response rules out that trigger,
forcing other explanations for the cause of the
Younger Dryas.
Research Design
Conducting this test involves reconstructing
the pattern of ice sheet retreat and dating
significant retreat positions.The first task employs
topographic digital elevation models from
the NASA Shuttle Radar Topography Mission
(SRTM) to identify ice margins and regional
deglaciation patterns.
In the Thunder Bay area (Figure 2), this approach
shows several subparallel ice margins
from just north of the Mesabi Range of northern
Minnesota northward to Lake Nipigon, reaf-
firming mapping by previous investigators. No
single meltwater choke point was found here;
instead, the topography allows several scenarios
for meltwater drainage depending upon the
rebound history. For example, the lowest present
topography is through Shebandowan Lake
and the Kaministikwia Rivers, and in this area
the ice margin slowly retreated.
In the Fort McMurray area (Figure 3), the ice
sheet had a lobate geometry between bedrock
uplands and filled the Athabasca River valley.
The key plug holding in water north of Fort
McMurray was the Firebag Moraine (Figure
3). Several large abandoned channels cut this
moraine, and the age of both the channels and
moraine constrains breaching of the moraine
The second task is to assign ages to these
various ice positions.We take 11,000 14C
years B.P. (R.Alley, personal communication,
2005) from the Greenland Ice Sheet Project
2 (GISP2) ice core record as the start of the
Younger Dryas.
Radiocarbon plateaus and resolution of
the accelerator mass spectrometer (AMS)
radiocarbon dating technique prohibit matching
the resolution of the ice cores. Rather,
samples from the first organic material that
accumulated on the deglaciated landscape
are obtained, to try to bracket the age of lakes
on either side of moraines. Because the oldest
organic material from each site may not have
been recovered, or does not coincide with ice
recession from that site, we employ a brute
force approach by sampling as many lakes as
possible.To date, we have recovered samples
from 84 sites. Keeping uncertainties in dating
as low as possible has been resource-intensive
but critical to this test.
Preliminary Findings
In the Fort McMurray area, three well-developed
ice margins (Stony Mountain, Firebag,
and Cree Lake Moraines) that spread over
some 100 km are currently assigned radiocarbon
ages of 10,030, 9595, and 9665 14C years
B.P., respectively (Figure 3). Consequently, it
appears that the plug was pulled and meltwater
could have flowed through the Clearwater
channel between 10,030 and 9700 14C years
B.P., consistent with the maximum age of 9900
14C years B.P. for flood gravel north of Fort
McMurray (Figure 3).
Even with the earliest bracket imposed
by the radiocarbon ages, deglaciation and
meltwater routing may have been 1000 14C
years later than the Younger Dryas.This routing
is more closely associated with the Preboreal
Oscillation, a brief return to cooling after the
Younger Dryas [Fisher et al., 2002], but precise
temporal relationships have yet to be determined.
In the Thunder Bay area, the current data
indicate sequential deglaciation with the
Shebandowan lowland submerged by a glacial
lake until 10,200 14C years B.P., based on a
combination of radiocarbon ages and varve
counts on the inorganic, laminated lake clays
below the radiocarbon sample level (Figure 2).
Fig. 2. Core sites and preliminary radiocarbon and beryllium ages from the Thunder Bay region.
Radiocarbon ages indicate a sequential northeast retreat of the ice sheet, while beryllium ages
show greater variability along one ice margin.The blue arrow west of Thunder Bay is the hypothesized
eastern outlet meltwater route.
Eos, Vol. 86, No. 40, 4 October 2005
One interpretation is that sequential recession
of the ice margin did not open an eastern outlet
until well after the beginning of the Younger
Dryas.An alternative interpretation has
been that recession from a glacial re-advance
associated with the Younger Dryas cooling is
being dated, not the original deglaciation.
At present, the data do not differentiate between
a re-advance or not. However, the sample
sites, some with glaciolacustrine sediments, plot
above known elevations of Lake Agassiz and the
subcontinental drainage divide.This implies a
different rebound history or deglaciation pattern
than has been proposed.
A central point for reconstructing the drainage
of Lake Agassiz is the significance of the
terrestrial macrofossils in fl uvial sediment
that indicate subaerial exposure between
two formations of lake clay deep in the Agassiz
basin.The oldest age on these deposits is
10,960 ± 300 14C years B.P., indicating a lower
water level at that time. However, reexamination
of this date within the context of other
numerous ages for this low lake level may
indicate the wood was reworked into younger
sediment, which would negate the temporal
coincidence of the lowering lake level and the
start of the Younger Dryas.
Thus, some key questions are:When and
from what water plane did the drop occur?
How fast was the drop? Where was the ice
margin relative to the outlets? What was the
basin volume at that time? All of these
factors constrain any estimate of freshwater
flux from Lake Agassiz into the oceans. Finally,
if both outlets were blocked at this time, how
extensive was the lake, and where was water
draining at that time? Obviously, an understanding
of the chronology of Lake Agassiz is
incomplete at this time.
Preliminary results indicate that ice recession
at both outlet areas is later than supposed,
and that large volumes of meltwater
were not catastrophically released from Lake
Agassiz at the beginning of the Younger Dryas.
Thus, if the Lake Agassiz floods did not upset
the circulation pattern, the question becomes:
What did? Could other pathways of the hydrological
cycle alter the thermohaline circulation
pattern at the beginning of the Younger Dryas,
or alter other climate fluctuations that preceded
Lake Agassiz?
These investigations indicate that the geological
understanding of past abrupt climate
changes is only preliminary.This does not
bode well for predicting future, abrupt climate
Broecker,W. S., et al. (1989), Routing of meltwater
from the Laurentide Ice Sheet during the Younger
Dryas cold episode, Nature, 341, 318-321.
Dyke,A. S., et al. (2003), Deglaciation of North America,
Geol. Surv. Can. Open File Rep., 1574, CD-ROM.
Fisher,T. G., D. G. Smith, and J.T.Andrews (2002), Preboreal
Oscillation caused by a glacial Lake Agassiz
flood, Quat. Sci. Rev., 21, 873-878.
Kennett, J. P., and N. Shackleton (1975), Laurentide
ice sheet meltwater recorded in Gulf of Mexico
deep-sea cores, Science, 188, 147-150.
Teller, J.T., and D.W. Leverington (2004), Glacial Lake
Agassiz: A 5000 yr history of change and its relationship
to the ∂ 18O record of Greenland, Geol. Soc.
Am. Bull., 116, 729-742.
Author Information
Thomas Lowell and Nicholas Waterson, University
of Cincinnati, Ohio;Timothy Fisher and Henry Loope,
University of Toledo, Ohio; Katherine Glover, University
of North Carolina at Charlotte; Gary Comer, GCI,
Waukesha,Wisconsin; Irka Hajdas, ETH-Hönggerberg,
Zürich, Switzerland; George Denton, Institute for
Climate Change, University of Maine at Orono; Joerg
Schaefer, Vincent Rinterknecht, and Wallace Broecker,
Lamont-Doherty Earth Observatory of Columbia
University, Palisades, N.Y.; and James Teller, University
of Manitoba,Winnipeg, Canada
Fig. 3. Fort McMurray area with an example of core stratigraphy from Crescent Lake on the proximal side of the Firebag Moraine.The lowest radiocarbon
age of 9595±75 is taken as a minimum age estimate for this moraine.The geometry and position of the ice sheet at the Firebag Moraine
would have prevented any meltwater draining northward at that time.

methane, ice melts, conveyer belt turn-offs 30.Jul.2008 20:08

penguin-looking for insight thnero@charter.net

From what I have read from all sides of the global warming debate, I have some questions. : Apparently, the world tundra has been exposed to heavy ice melts several times over the last million years. I assume major methane releases have taken place during these meltdowns. Any idea on the effect of these releases, if any? At the end of the Younger Dryas, a major warmup and, I assume, major glacier melt took place over the course of only 50-100 years. If this is true, much more freshwater poured into the oceans than is occuring today. Why did we not plunge back into another Younger Dryas event or reglaciation? New theories suggest the Black Lake(my term) became the Black Sea during this meltdown in a massive flooding event, so the freshwater intrusion into the world oceans after Younger Dryas must have been immense. The only thing that I can see that most everyone agrees with is that a major reglaciation will almost certainly occur and that it could occur as early as, well, tomorrow(or 40,000 years from now). My personal list of civilization killers in order of probability are: 1/4 mile wide asteroid impact, supervolcanic eruption, reglaciation, nuclear event(war, reactor meltdown etc.) pandemic of enormous size, global warming, 1/2 mile impact event, methane release, arrival of the antichrist, 1 mile wide impact event, gamma ray assualt, 5 mile wide imapct event.