How Global Warming Can Lead to a Big Chill

Science - Reuters ^ | Fri Dec 3, 2004 | Anon Science Stringer

[dufekin]

Okay. This is a very poorly written article, and I can't tell from the contents what constitutes news or its significance. Here's the gist of the prevailing view among scientists of the happenings of 8200 years ago.

The enormous land-fast Luarentide Ice Sheet covered much of Canada east of the Rockies. This ice sheet began melting gradually a couple millenia earlier, and although some of the melt water flowed directly to the sea, the enormous inland Lake Agassiz formed on the southern periphery of the ice sheet, centered vaguely near the present Lake Manitoba in Canada.

In a relatively sudden burst, this lake carved one or several deep paths to the Atlantic Basin when ice blocking the path burst or melted. Literally hundreds of trillions trillions of cubic meters--tens of quadrillions of gallons--of frigid fresh water suddenly rushed into the Atlantic Ocean.

The important feature of the Atlantic Ocean is the thermohaline circulation, by which salty, warm water sinks because of its density. Locally fierce, dry winds in a few relatively small areas cause much evaporation of the warm water, leaving that which remains more saline, and hence denser than the surrounding water. This water, dense by virtue of its salinity, sinks. This phenomenon occurs ONLY in the North Atlantic. (Intense sinking in the Southern Ocean and on the periphery of glaciers does occur, but results from cold, fresh glacial melt water rather than warm, saline water drawn poleward from the tropics.)

The sinking in the North Atlantic creates a vacuum of sorts that the Gulf Stream fills. Shuttering the sinking in the North Atlantic would decrease the net northward transport of water throughout the Atlantic from the Cape of Good Hope to the shores of Iceland. The Gulf Stream, therefore, ranks among the strongest ocean currents in the entire World Ocean.

The flood waters from Lake Agassiz supplanted the warm, saline waters from the tropical Atlantic and so suspended the thermohaline circulation. These cold, fresh waters thereby slowed the Gulf Stream dramatically. The flood waters also increased sea levels throughout the world by adding more water volume to the oceans.

[Archangelsk]

The amount of precipitation that can be held in the air is a direct reflection of the temperature. The colder the airmass (in this case continental artic or cA) the less water vapor it can hold. Global warming, which has always happened throughout the geophysical history of the Earth, would cause the temperature to rise at the poles thus allow more water vapor to be held (this is the relationship between temperature, dew point and relative humidity).

The real controversy, if you can call it that, is whether human activity accelerates global warming. The answer, and one nobody wants to hear, is that any activity causes global warming to acclerate. Thus, dinosaurs pooping, volcanoes exploding, ants farting and yes, humans burning hydrocarbons, accelerate the process.

One other thing, most people look at air temperatures and start yelling and screaming about global warming. This is good sport for the ill-informed. The real index to look at are the sea surface temperatures. Here's today's:

If you were to tell me 10 years ago that the SST on December 4, 2004 off the coast of Maine would be hovering around 60 degrees I would have told you that you were barking mad, as it is, it is. Global warming is happening and I wouldn't be concerned about the Earth (it's been around for 5 billion years), I'd be concerned about mankind (which may not make it out of the 21st century).

[dufekin]

The Gulf Stream recovered within a century or two after the great Lake Agassiz bust. The Agassiz bust was itself a part of the relatively brief recovery from a Dansgaard-Oescher event. That recovery continues to this day and will continue until the next ice age. The past several thousand years of climate have been remarkably steady, without the sudden shifts between ice ages and interstidials that characterized the previous hundred thousand years or so.

Scandinavian temperatures during the Medieval Warm Period, contrary to popular belief in liberal circles, easily exceeded those observed today. The Medieval Warm period ended in the little ice age, the beginning of which roughly coincided with the Black Death bubonic plague.

[Archangelsk]

Which may, may, have been a direct result of a meteor impact on the moon around 900 - 1000 AD, which flung ejecta out, which eventually struck the Earth causing the dark ages. This is not so far fetched because of the overwhelming use of metaphorical dragons from the writings of the period (also the short growing seasons in Europe, which led to some pretty lean times food wise).

[dufekin]

Nope. This melting ice, trapped in Lake Agassiz, an enormous, frigid, and fresh inland sea on the edge of the vast Laurentide Ice Sheet, burst into the seas suddenly. Although it caused a temporary and sharp cooling that lasted a century or so (and a significant rise in sea levels), it did not result in an ice age. The climate system was undergoing long-term recovery from the Younger Dryas ice age event. Temperatures resumed recovery resumed a couple centuries after the shock, having returned generally to levels observed before the Lake Agassiz climate shock.

[dufekin]

So long as Antarctica remains centered about the South Pole, melting of its ice sheets will be insignificant, even in many of the least realistic global-warming doomsday scenarios.

[dufekin]

Wait a minute. Those warm waters "off the coast of Maine" are actually cooler than normal. You're looking at the Gulf Stream, located several hundred miles off the Maine coast. The Gulf Stream normally is that warm.

[Pharmboy]

Thanks for the cogent, well written explanation. One questions: are the remnants of the channels that brought these quadrillions of gallons to the Atlantic from Canada in evidence today? The Great Lakes perhaps?

[dufekin]

The Great Lakes are only some of those channels. Other such channels (according to prevailing theory) may include the Mohawk/Hudson valley in New York, Pine Creek in Pennsylvania (near Williamsport), and the Saint Lawrence Seaway. Other waters apparently drained through the Mississippi and Mackenzie basins. I'm not exactly sure what the theories are, and it seems that everyone has a different one.

[dufekin]

There appears to be a roughly 1500-year oscillation in global temperatures. We've got a while until this present warm phase ends. The Medieval Warm Period was another such warm phase.

[Archangelsk]

Go to the Unisys model instead, it's much more accurate. I know that the servers are currently screwed - slowing the download - but it shows a temperature between 18 and 21 degrees C. Also, at the micro-level, the SST recorded from the buoy 120 NM off New Smyrna Beach, Florida is currently 76 degrees F, which is mighty warm for this time of year.

[henderson field]

Of course there were SUVs millions of years ago. Any fool knows what. The real question is what kind of SUVs? BMW? Lexus? Jeep? Volvo? Hummer? What kind?

[watchin]

This is retarded. If there were global warming, and it began to melt the polar ice caps, the chilling effect of the arctic waters would soon negate the global warming, bringing the earth back to equilibrium.

This theory is something like believing that if your fridge goes out, all the ice in your freezer will melt and freeze everything in your refrigerator.

duh.

[watchin]

It means that if it gets either hotter or colder, it's global warming, and therefore Bush's fault.

[blam]

Did Asteroids And Comets Turn The Tides Of Civilisation?

[rockrr]

"
The flood waters from Lake Agassiz supplanted the warm, saline waters from the tropical Atlantic and so suspended the thermohaline circulation."

And no doubt caused significant shrinkage to anyone who happened to be swimming at the time....

[Gondring]

Several good points, but I think it's best to clarify a few things. A better term than "Global Warming" is "Climate Change"... Even the doomsayers don't claim it will be a uniform change, but that we will have more extreme weather, and that in areas, there will be cooling (and precipitation changes, too).

I think it's pretty obvious that there is climate change occurring, but whether humanity has caused it is somewhat debateable. Regardless, we have to live with it...even if it's currently rather "cold," and warming would make us more "normal" for the history of the earth.

The question about a small change in temperature misses the point that even if it's still "too cold to snow" (i.e., dry air) in the 70-below areas of the antarctic, there's a ring around the pole that is in the appropriate range where 2 degrees WILL change things. Also note the good ol' puzzle dealing with isostasy and displacement:

Archimedes is out on a pond in a boat with a big chunk of granite. He then throws the granite overboard, into the pond. Does the water level of the pond go up, down, or stay the same?

The water level of the pond drops when the rock is thrown in, since granite's density (specific gravity) is about 2.7 times water's.

Now just apply the same thoughts (in reverse, since ice is lower density than seawater) to see why it makes a difference whether ice is floating in the ocean or up on the icecap.

[boop]

How come the great plains were formed under the pressure of tremendous glaciers, during prehistoric ice ages. When the ice ages ended, the land dried up. Unless that's an ocean I'm missing over Kansas.

[Gondring]

How come the great plains were formed under the pressure of tremendous glaciers, during prehistoric ice ages. When the ice ages ended, the land dried up. Unless that's an ocean I'm missing over Kansas.

Sorry, but I'm missing your point. If you have a fishtank with water and an rock (partially submerged, making an island), and there's an ice cube floating in it and the ice cube melts, that's a different situation from if the ice cube were sitting on the rock and melted--with the water going down into the water.

Perhaps you're referring to the isostatic rebound--and the glaciers did depress the earth's surface (which has still not yet rebounded fully), and there's the groundwater to consider, etc., but the bottom line is that the meltwater from the continental glaciation did, in fact, increase sea level. It's also a fact that the configuration of the ocean currents has a major impact on climate--evident from the huge effects of the creation of the Panama isthmus a few million years ago.