The information in this post is taken from the article
The New Ice Age which can be found in the September, 2002 edition of
Discovery magazine.
A growing number of scientists - including many at the
Woods Hole Oceanographic Institution on Cape Cod in Massachusetts - believes conditions are ripe for a prolonged cool down, or small ice age. The next cooling trend will probably not produce a huge ice sheet such as existed 12,000 years ago, it could drop average temperatures 5 degrees Fahrenheit over much of the United States and 10 degrees in the Northeast, northern Europe, and northern Asia.
Terrence Joyce, who chairs the Woods Hole Physical Oceanography Department, states "It could happen in 10 years. Once it does, it can take hundreds of years to reverse."
A drop of 5 to 10 degrees could have devastating consequences. A 2002 report titled
Abrupt Climate Change: Inevitable Surprises," produced by the National Academy of Sciences, pegged the cost from agricultural losses alone at $100 billion to $250 billion while also predicting that damage to ecologies could be vast and incalculable: disappearing forest, increased housing expenses, dwindling freshwater, lower crop yields, and accelerated species extinctions. A quick climate change wreaks far more disruption than a slow one.
Climate science is complex, and the onslaught of a little ice age is not certain, at least at this state of research. Scientists all over the world are studying the problem, but perhaps nowhere in the U.S. is more energy, equipment and brainpower directed at the problem than here at Woods Hole. The oceanographers on staff subsist largely on government grants and are beholden to no corporation, making the facility "uniquely independent," says David Gallo, director of special projects.
The institute has three research ships that use core samplers that extract long columns of layered sediments from the sea floor. Technicians also tinker with arrays of multiple independent water samplers, which are dropped into the North Atlantic, hoping to get a sharper picture of the potential for a little ice age. "We need to make this a national priority," says Joyce, but "...with enough data, I think we can make a more specific and confident prediciton about what comes next." Policymakers armed with more accurate data could make adjustments to prepare for the inevitable.
But first things first. Isn't the earth actually warming? Indeed it is, says Joyce. He explains that such warming could actually be the surprising culprit of the next mini-ice age. The paradox is a result of the appearance over the past 30 years in the North Atlantic of huge rivers of
freshwater -- the equivalent of a 10-foot-thick layer -- mixed into the salty sea. A prime suspect in the appearance of this water is melting Arctic ice, caused by a buildup of carbon dioxide in the atmosphere that traps solar energy.
The freshwater trend is major news in ocean-science circles. Bob Dickson, a British oceanographer, has termed the drop in salinity and temperature in the Laborador Sea -- "arguably the largest full-depth changes observed in the modern instrumental oceanagraphic record."
The trend could cause a little ice age by subverting the northern penetration of Gulf Stream waters. Normally the Gulf Stream wanders north along the eastern coasts of the U.S. and Canada. Surrendering heat to the air as it goes, prevailing winds waft this heat over Europe. Many scientists believe that's why winter temperatures in Europe are as much as 36 degrees Fahrenheit warmer than those in North America at the same latitude.
Having lost its heat to the air, the now-cooler current becomes denser and sinks into the North Atlantic by a more or more in a process called
thermohaline circulation. This column of sinking cold water is the main engine powering a deepwater current called the Great Conveyor that snakes through all the world's oceans. But as the North Atlantic fills with freshwater, it grows less dense, making the waters carried northward by the Gulf Stream less able to sink. The mass of freshwater sits on top of the ocean like a big thermal blanket, threatening the thermohaline circulation. This in turn could make the Gulf Stream slow or veer southward. At some point the whole system could simply shut down, and do so quickly. "There is increasing evidence that we are getting close to a transition point, from which we can jump to a new state. Small changes, such as a couple of years of heavy precipitation or melting ice at high latitudes, could yield a big response," says Joyce.
Another oceanographer, Ruth Curry, uses a four map array to show the North Atlantic each decade since the 1960s. Orange and yellow on the map mean warmer and saltier. Green and blue mean colder and fresher. With each subsequent map, green and blue spread farther. "It's not just in the Laborador Sea...this cold freshening area is nor invading the deep waters of the entire subtropical Atlantic.
Joyce states that it could literally take hundreds of years to get rid of all this fresh water. So while the globe as a whole gets warmer by tiny fractions of 1 degree Fahrenheit annually, the North ATlantic region could, in just ten years, get up to 10 degrees colder.
Seafloor sediment cores give evidence that this has happened before...most notably during the little ice age that lasted from 1300 to 1850 A.D. Tiny invertebrates called foraminifera (amoebas with shells) are found in these sediments. By measuring the proportions of oxygen isotopes scientists are able to ascertain the temperature at which the tiny animals in each layer formed their calcium carbonate shells to an acdcuracy of less than 1 degree Fahrenheit.
Plenty of data has been uncovered about abrupt temperature changes over the past 1,000 years, including for a little ice age that averaged about 4 degrees Fahrenheit colder than the present.
Clearly, the little iace age wasn't kicked off by humans releasing greenhouse gases. But natural climate cycles that melted Arctic ice could have caused thermohaline circulation to shut down.
An event that took place in the late 1960's perhaps provides a better example that a climate can cool quickly. A huge mass of near-surface fresh water appeared off the east coast of Greenland. The Great Salinity Anomaly, as it was called, drifted southward, settling into the North Atlantic in the early 1970s. It interfered with the thermohaline circulation by arresting deepwater formation in the Laborador Sea. Drifting in a counterclockwise direction, it re-entered the Norwegian Sea in the late 1970s and eventually vanished.
Shutting the system down for a few years, the Great Salinity Anomaly brought very cold winters, particularly in Europe. That mass, fortunately was small enough to disperse in a short period of time. The one accumulating up there now, however, "is just too big," says Joyce.
"We can't know the point at which thermohaline shutdown could actually start," says Ruth Curry. "But we should plan for it."
More information about
transition climate models can be found here:
http://books.nap.edu/books/0309074347/html/index.html Regards, Shuckins
