The world’s weather patterns are twisting and turning and obviously we cannot expect to have what we consider status quo weather any longer. We generally consider climate changes as taking place over hundreds or even thousands of years. However, since the early 1980s, earth’s climate history has changed.
Just yesterday, snow has settled the city of Obihiro in of Hokkaido for the first time in May in eight years. The temperature was overnight low at minus 3.2 degrees Celsius. The temperature is about five degrees lower than the average for the time of year. The observatory says another low pressure system is expected to bring more snow to areas facing the Sea of Okhotsk and the Pacific.
Current theories on the cause of abrupt climatic change focus on sudden shut downs and start-ups of the Meridional Overturning Circulation, referred to as the thermohaline circulation: http://www.esr.org/outreach/glossary/thermohaline.html
It is a global network of density-driven ocean currents transports a tremendous amount of heat northward, keeping the North Atlantic and much of Europe up to 5°C warmer, particularly in the winter. A sudden shut down of this current would have a ripple effect throughout the ocean-atmosphere system, forcing worldwide changes in ocean currents, and in the path of the atmospheric jet stream.
Studies of North Atlantic Ocean sediments have revealed that the Meridional Overturning Circulation has shut down many times in the past, and that many of these shut downs coincide with the abrupt climate change events noted in the Greenland ice cores.