14 DAY TRIAL // Between 1200 and 1850, Northwestern Europe had experienced a mini ice age. Legend has it that almost five centuries ago, England's King Henry VIII crossed the Thames River by horse on the frozen surface. The Thames used to freeze so often that London even had carnivals on the ice called the Frost Fairs. Here's a 1677 painting of the Frozen Thames by an unknown author (the Museum of London). The last Frost Fair was held in February 1814 and lasted only four days.
A new study published in Nature argues that the cause of the mini ice age had to do with the weakening of the Gulf Stream. The Gulf Stream is a current in the Atlantic Ocean that takes warm water from the tropical mid-Atlantic up to Europe's western coastline. The warm water heats up the atmosphere and assures the mild western European weather in spite of the high latitude (Western Europe is at the same latitude as chilly Labrador).
David Lund of the Californian Institute of Technology (Caltech) and his colleagues have studied the sediments from the region where the Gulf Stream enters the North Atlantic Ocean, called the Florida Straits. These sediments are made of a calcified species of plankton called foraminifera. The scientists detect the amount of the oxygen-18 isotope present in the sediment cores and use this data to deduce the past salinity and temperature of the seawater. Thus, the amounts of oxygen-18 can be used to determine the density of the seawater and the flow.
Scientists have found that during the medieval Little Ice Age, the Gulf Stream's flow was 10 percent lower in volume than today's one. What caused that past diminishing of the Gulf Stream is still unknown.
This finding has a relative significance for our situation today, although more data is needed for reaching a firm conclusion on this issue, because oceanographers at Britain's University of Southampton have found a year ago that a key branch of the Gulf Stream system, the North Atlantic Drift, had lost 30 percent of its flow since 1998. They have traveled with a survey ship along 24 degrees latitude north on a line from the Bahamas to tropical West Africa, measuring salinity and temperature every 50 kilometers (31 miles). (Such data is also available for the following past years: 1957, 1981, 1992 and 1998.)
This diminishing of the Atlantic current is probably caused by the melting of the Greenland's ice cap and of the Siberian permafrost and thus, it is ultimately caused by global warming.
So, paradoxically, global warming might cause another European Little Ice Age. As I have described elsewhere, the climate change has two superimposed trends - on one hand, there is the global trend that involves the global average temperature and on the other hand, there are the fluctuations of temperature from place to place, given a certain global average temperature. So, as the global average temperature rises, if Europe will become colder it means that other regions of the world, such as Africa, will become much hotter.
Here is a clip of Al Gore explaining the Gulf Stream: