Abrupt Climate Changes
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Throughout recorded history, and in studies of geological and other records from much earlier periods of the Earth’s history, there have been a number of abrupt climate changes. These significant and widespread shifts in climate heavily impacted many parts of the world. Current studies of these changes draw from details revealed from ice core samples, especially from Greenland and northern Canada, and also from records compiled showing signs of geological changes. More recent information has emerged from examinations of the fluctuations in the size of tree rings, and from historical accounts. The quantity of these abrupt climate changes has led some academics, often labeled climate change skeptics, to explain the current global warming in terms of these trends. They suggest or state that the current changes are, or could be, merely a part of a cycle of global warming and cooling, similar to those that have occurred over hundreds of thousands of years. Explaining global warming in the 1990s and 2000s by studying these abrupt climate changes gained much publicity around the world through the article “A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates,” which was written by 10 leading scientists: G. Bond, W. Showers, M. Chesby, R. Lotti, P. Alamsi, P. de Menocal, P. Priore, H. Cullen, I. Hajdas, and G. Bonani, and published in the journal Science in November 1997. This article, and related work, led to a substantial body of research on abrupt climate changes-when the Earth’s temperature has either significantly increased or decreased over a short period of time-and also the possible causes of these changes. A development of this theory came from two other scientists associated with those skeptical of global warming, S. Fred Singer of the University of Virginia, and Dennis Avery of the Hudson Institute in New York. They raised the possibility of a 1,500-year climate cycle, especially in the north Atlantic region, with hot temperatures every 1,500 years, The present global warming could be a part of this cycle. A part of this theory rests on the extreme weather patterns experienced around the world from 535 to 536 c.e. They are recorded by the Byzantine historian Procopius, in Irish annals, and in records kept in China—all showing that the climate change occurred across a large number of areas. These historical accounts are confirmed by a tree ring analysis undertaken by the dendrochronologist Mike Baillie from Queen’s University of Belfast, Northern Ireland, which showed little growth in Irish oak trees during this period. Similar data emerged from a study of tree ring samples conducted on trees from Scandinavia, California, and Chile. The fall in temperature during these years seems to have led to a widespread series of famines around the world, and the collapse or destruction of a number of empires including that of the Persians, and the Mesoamerican city of Teotihuacan. There is no accepted cause of this instance of abrupt climate change, although there has been the suggestion that it could have been caused by the large-scale eruption of a volcano, such as Krakatoa, off the coast of Java (modern-day Indonesia); this idea formed a central part of the work of David Keys in his book Catastrophe: A Quest for the Origins of the Modern World(1999). Other scientists have been critical of these conclusions.
History
Going back further in history, there was a prolonged drought in the 22nd century b.c.e., which had a dramatic effect on the Old Kingdom of Egypt. It led to about 40 years of famines and social dislocation, which produced the emergence of the unified Kingdom of Egypt as a new political identity capable of financing irrigation projects and the like to overcome these problems. There have also been more recent changes in temperature, with suggestions that the collapse of the Mayan Empire in Mexico in the 8th and 9th centuries was possibly caused by a regional abrupt climate change, although others have pointed to the greater likelihood that this stemmed from overpopulation, foreign invasions, epidemics, and internal insurgencies. The idea of localized problems is reinforced by the fact that there is little evidence of an abrupt climate change elsewhere in the world at that time. There have also been studies of what has been deemed the Little Ice Age, which took place from about 1600 until about 1750, with the freezing of rivers such as the River Thames in England, of canals in the Netherlands (shown in contemporaneous paintings), and the southern section of the Bosphorus in 1622. As the process seems to have been gradual, it might also have been responsible for the end of the Viking colonies in Greenland during the 15th century. The concept of abrupt climate change goes back far further than recorded history. The last Ice Age in the Pleistocene period, which ended in about 10,000 b.c.e., ended a period of cold weather that is believed to have started with a long glacial advance from about 70,000 b.c.e., reaching a peak in 18,000 b.c.e., when most of northern Europe and considerable portions of modern-day Canada were covered with glaciers.
Debate
As a result of these studies, there are scientists who argue that global warming is just a phenomenon that has taken place before, and will take place again. They believe that global warming is not caused by the emission of increasing amounts of carbon dioxide (CO2) and other greenhouse gases. There are also many who suggest that while warming is a regular phenomenon, it has been exacerbated by increasing greenhouse gas emissions. Although abrupt climate changes have happened throughout history, scientists who argue that global warming is extremely serious point to the rapidity of recent climate changes, and that they are occurring at an increasing rate throughout the world. In contrast to the changes that have been studied, measured, examined, and analyzed over the last 20 years, events such as the Little Ice Age took place gradually over at least 120 years, if not longer. Some date the start of the period back to 1250, when the Atlantic pack ice started to grow, and suggest that it was a cause of the Great Famine of 1315 to 1317, with the serious glacial expansion taking place only since 1550, and the first significant climatic changes in non-Arctic Europe beginning in the early 17th century. By contrast, similar fluctuations in temperature (rising now, instead of falling as in the 1600s) in recent decades, have happened over a very short time, and the loss of large amounts of Antarctic ice have been evident over a 10-year period. The ability to track many of these changes from satellites has allowed geographers and scientists to identify other problems, such as the ozone hole. The theory of abrupt climate change indicates that there are many forces that contribute to global warming around the world, in addition to human-caused CO2 and other emissions. However, researchers have been increasingly able to monitor these changes since the early 1990s, and the fact that the symptoms of climate change and global warming are currently being recorded around the planet, and are accelerating, has led many scientists to suggest that global warming cannot be solely explained by the theory of abrupt climate change. It has further led to the theory that these human-made causes might be coinciding with a cyclical period of abrupt climate change, leading to a worsening of problems faced by people in most parts of the world.
