Between the years 1300 and 1850, Europe experienced a general cooling of its climate. Average temperatures across the northern hemisphere declined about 2°C in Europe. The name given to this period is the ‘Little Ice Age.’
Visible effects of this cooling were noted all across Europe. The Baltic Sea froze over in winters, along with rivers and lakes across Europe. Also, winters were bitterly cold, and the summers were cool. Because of the colder climate, crop failure was common, leading to famine, population decline, and social unrest. Mountain snowlines dropped to lower elevations, and glaciers expanded, wiping out villages and farms. Additionally, the Arctic Ocean ice packs extended southward, making winter shipping impossible in some areas.
The causes of the Little Ice Age are speculative. Reduced solar radiation, increased volcanic activity, changes in the atmospheric circulation, and weakening of the Gulf Stream have all been evoked to explain this period of significant cooling. Gulf Stream weakening is an interesting possibility, however, since it relates to present-day ocean circulation patterns and presumably could happen again.
Ocean Circulation
Temperature differentials between warm water in the tropics and cooler water at the poles drive a complex set of ocean currents. The term ‘Thermohaline Circulation’ refers to the temperature and salinity differences that drive this circulation. So, the basic premise is that cold, salty water is dense and sinks to the ocean floor. The sinking water then creates a void and causes warmer surface water to flow in and fill that void. This cause-and-effect cycle sets up a continuous current of warm water flowing from the tropics to the polar areas where it cools and sinks, thus causing more warm water to flow from the hot lower latitudes.
The North Atlantic Gulf Stream is an excellent example of thermohaline circulation. Warm water from the tropics is transported northward by the Gulf Stream. The tropical water is extra salty due to evaporation in the hot tropics. This warm water makes its way to the edge of the Arctic, where it gives up its heat to Europe. As the saline water cools, it becomes denser and sinks to the deep ocean floor, causing the flow of more warm water from the tropics to fill the void.
The Gulf Stream is a conveyor belt for heat, moving warm water from the southern tropics to the polar Arctic. Europe depends on this heat. One theory for the Little Ice Age is that the Gulf Stream weakened during this period, therefore reducing the heat available to Europe.
Could it happen again?
Arctic warming may work against Europe. As the Arctic waters warm and more ice melts, two factors appear that work against the Gulf Stream. Warmer water is less dense than cold water, and freshwater from ice melt makes ocean surface water less dense. If the water at the north end of the Gulf Stream is not dense enough, it won’t sink to the ocean floor. A lack of dense water would effectively cut off the Gulf Stream and create a colder Europe. It will certainly be ironic if global warming cools Europe.
ArcheanWeb:
Riding the global conveyor belt (Source:ArcheanWeb) – https://archeanweb.com/2020/04/06/riding-the-global-conveyor-belt/ Also:
Thermohaline circulation (Source: ArcheanWeb) – https://archeanweb.com/2020/04/03/thermohaline-circulation/ Also:
Sources:
Was a change in thermohaline circulation responsible for the Little Ice Age? (Wallace S. Broecker – PNAS) – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC34299/ Also:
Failing ocean current raises fears of
Gulf Stream Weakened in ‘Little Ice Age’ ( Michael Hopkin – Nature) – https://www.nature.com/news/2006/061127/full/061127-8.html Also:
Are we on the brink of a ‘New Little Ice Age?” (Woods Hole Oceanographic Institution) – https://www.whoi.edu/know-your-ocean/ocean-topics/climate-ocean/abrupt-climate-change/are-we-on-the-brink-of-a-new-little-ice-age/ Also:
How the Little Ice Age changes history (John Lanchester – The New Yorker) – https://www.newyorker.com/magazine/2019/04/01/how-the-little-ice-age-changed-history Also:
The Gulf Stream slowed during the Little Ice Age (Phil Berardelli – AAAS: Science) – https://www.sciencemag.org/news/2006/11/gulf-stream-slowed-during-little-ice-age
