According to a recent paper, there is considerable evidence for abrupt climate change. The most recent episode occurred in Northern Europe prior to the Little Ice Age, where - after a gradual rise in temperatures over several centuries - temperatures dramatically flip-flopped into Arctic chilliness in a matter of years, according to ice core samples.

Two recent and progressively colder winters in both America and Europe have doomsayers and scientists calculating the odds of it happening again.

Image Courtesy of BBC

The mechanism of abrupt climate change is, according to climate scientists, a failure of an ocean current called "The Great Conveyor Belt" (also known as thermohaline circulation).  This ocean current is in trouble as freshwater glaciers and ice sheets melt.  Excess freshwater entering the saltwater ocean interrupts how the current operate, threatening to stop its circulation. 

If the current stops bringing warm, equatorial air northward via the Gulf Stream, it would lead to increasing cold in Northern Europe and the Atlantic Coast of the United States.

For example, Europe and Alaska are at the same latitude, but Europe is warmer because of this thermohaline circulation, which is the result of differences in water temperatures and salinity between the North Atlantic and the Pacific. When the Great Conveyor Belt circulates in the ocean, warmer equatorial waters raise the temperature of the Atlantic Ocean, most notably between Europe and the Atlantic coastline off New York.  Winds circulating around and over this warmer sea area bring warmer temperatures to adjacent landmasses in Europe and America.

If thermohaline circulation were to fail as some anticipate, currently temperate areas of the globe would become close to uninhabitable, and food production in those areas would fail almost entirely. According to one source, the Gulf Stream has already slowed by six million tonnes of water per second over the past three decades, and computer modeling projections suggest that another global temperature rise of as little as 3 degrees Celsius creates a 50-percent risk of the current collapsing altogether.

This possible scenario worries not only climatologists, but security agencies around the world, who foresee in the collapse of thermohaline circulation - also known as the Atlantic Meridional Overturning Circulation, or MOC - a potential for food and land disputes in Europe and America similar in ferocity to the food riots in the summer of 2008 in Haiti and Africa, and the constant displacement of the citizens of Somalia over the last decade.

At the Pentagon, concerns that the current might collapse in the near future, leaving the Atlantic states enjoying Siberian summers and deep-freeze winters, prompted a 2003 report suggesting the possibility of food and water shortages, as well as other resource wars when energy suppliers are overtaxed to deliver heat to businesses and homes.

The report adds a curiously disturbing warning: "Nations with the resources to do so may build virtual fortresses around their countries, preserving resources for themselves. Unlikely alliances could be formed as defense priorities shift and the goal is resources for survival rather than religion, ideology, or national honor."

A Cardiff University investigation of ice core samples lead to the theory that, with collapse of the currents, much of the heat circulated around the planet could be trapped in the Southern Hemisphere.  So while the north would shiver, the south could bake.  No one - even the experts - knows precisely what would happen if the many-named ocean current system failed, but one thing is certain. Life as we know it would come to an abrupt and painful end. 

Is it time to panic? Well, there is supporting historical evidence that the Gulf Stream has switched off at least twice over the past ten thousand years, neither time due to anthropogenic (man-made) causes. Given current levels of atmospheric carbon dioxide (386.92 parts per million, a rate that has grown exponentially since 1950) - not to mention the amounts sequestered in now-melting permafrost - this ocean current destabilization could well happen again.

In spite of that, climate modeling experts and the International Panel on Climate Change, or IPCC, argue that complete collapse is unlikely. Most scenarios suggest an additional reduction in circulation strength of 25 percent, at most, by 2100, after which things level off. Even worst-case scenarios predict a final strength of about 50 percent of today's volume, or an overall decrease since 1978 of about 65 percent.

The dire warnings brought home to moviegoers in the recent film, The Day After Tomorrow, are mostly the stuff of Hollywood fantasy. However, recent events, like the breaking away of the Wilkins Ice Shelf in the Antarctic, and last summer's fissures in the Ward Hunt ice shelf in the Arctic, make it apparent that no one can be certain if we are headed for mere climate change or complete climate destabilization.

Related Reading:
Oceans: The Key to Understanding Our Climate
Ocean Cooling: A Science Lesson for Denialists/Delayers