Gulf Stream out of circulation?

Paleoclimatologists at Oregon State University released a survey last month which added weight to the theory that the Gulf Stream may slow or stop entirely. Publishing a paper in the respected Proceedings of the National Academy of Sciences journal, the Oregon scientists provide data that indicate why current patterns changed in the distant past in extraordinarily short timeframes. The trigger for current change is a surge of fresh water which reduces the ocean’s salinity. The study is of interest today due to concerns that global warming could perversely re-create the conditions for a new ice age.

The research relies heavily on the activity of a process called thermohaline circulation (THC). THC governs the global deepwater currents and plays an important role in supplying heat to the polar regions, and in regulating sea ice. THC causes a huge conveyor belt of warm, less-salty surface water from the tropical Atlantic Ocean to the far North Atlantic, where it finally becomes so cold and salty that it sinks, moves south, and continues the circulation pattern. Large influxes of fresh water could slow or even stop the current. The loss of the Greenland ice sheet could provide the trigger for such an event.

The northbound belt of the THC is the Gulf Stream. The Gulf Stream is one of world’s most intensely studied currents. Visible from space, the 100-200km wide current begins in the Caribbean and moves north east keeping the seas of high latitude Ireland, Britain and Scandinavia ice free. Any disruption to the current would be disastrous for these countries. But it has happened before.

Peter Schwartz and Doug Randall produced a 2003 paper for the Pentagon called An Abrupt Climate Change Scenario and Its Implications for United States National Security. The subtitle of the document was called “Imagining the Unthinkable”. It envisages a scenario where temperatures drop over Asia, North America and northern Europe, while rising over the southern hemisphere. It will cause droughts, severe storms and rising sea levels. Europe will become like Siberia, China will be hit by famine and Bangladesh will be drowned. While fortunate nations batten down the hatches, the report says “less fortunate nations, especially those with ancient enmities with their neighbours, may initiate struggles for access to food, clean water, or energy”.

The report states that about 12,700 years ago there was substantial cooling in a period that is now known as the Younger Dryas. The period is associated with an apparent collapse of the thermohaline circulation. There was a cooling of at least 15° Celsius in Greenland, and substantial change throughout the North Atlantic region which lasted 1,300 years. During the Younger Dryas the temperature dropped by about 3° C every decade before flattening out for an extended cold period of about a thousand years. Most of Europe was icebound and icebergs would have been found off the coast of Portugal.

The most recent cooling period began in the 14th century and the North Atlantic region experienced a cooling that lasted until the mid-19th century. Known as the Little Ice Age, it brought severe winters, sudden climatic shifts, and profound agricultural, economic, and political impacts to Europe. It was the probable cause of the demise of the Norwegian settlement in Greenland and the severe climatic conditions caused the Great Famine of Northern Europe in 1315-1322.

Schwartz and Randall posit a vision of the future which considers abrupt climate change. Though they don’t predict how exactly it might happen, the scenario involves all the floating ice disappearing from the northern polar seas. The THC grinds to a halt after 2010 disrupting the temperate climate of Europe. After another ten years Europe’s climate resembles Siberia while the South deals with increased warmth, precipitation, and storms. Millions will be on the move, escaping from the cold of the north and a waterless Africa. Crop yields will fall leading to food shortages. Access to minerals will be disrupted by ice and storms. As the Earth exceeds its carrying capacity, wars will become more frequent over diminishing resources.

One of the authors, Peter Schwartz told a symposium at the World Resources Institute, his worst-case scenario report was buried in the Pentagon bureaucracy. Many planners blasted it as being too unrealistic because it wasn’t based on more gradual climate change scenarios. But as scientists such as the Oregon State University paleoclimatologists have shown, these scenarios don’t necessarily get to grips with the extreme events that characterise the climate history of Earth.