What is abrupt climate change?

“Abrupt climate change” is a term referring to rapid shifts in the Earth’s climate. The U.S. Climate Change Program defines “abrupt climate change” as a, “large-scale change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades, and causes substantial disruptions in human and natural systems.”[i] According to the Woods Hole Oceanographic Institution, “recent and rapidly advancing evidence demonstrates that Earth's climate repeatedly has shifted dramatically and in time spans as short as a decade.”[ii]

[i] Clark, Peter U., Weaver, Andrew J. et al., “Abrupt Climate Change,” http://downloads.climatescience.gov/sap/sap3-4/sap3-4-final-report-exec-sum.pdf (accessed Nov. 6, 2010)

[ii] http://www.whoi.edu/page.do?pid=12455 (accessed Nov. 6, 2010).

Abrupt climate change is the subject of a 2003 report commissioned by the Pentagon entitled “An Abrupt Climate Change Scenario and Its Implications for United States National Security” (“the Pentagon Report”).[i] The Pentagon Report cited a number of instances in relatively recent history in which the Earth’s climate underwent abrupt climate changes. An event known as “The Younger Dryas” occurred about 12,700 years ago. Average temperatures in Greenland dropped about 5 degrees Fahrenheit a decade, with a total drop in average temperature of at least 27 degrees. There was substantial change throughout the North Atlantic region. As a result, cold, dry weather persisted in the region for more than 1,000 years. The extent of the spread of cold is illustrated by the fact that icebergs were “found as far south as the coast of Portugal.” The evidence suggests that The Younger Dryas followed a period of global warming.

A similar, although more abrupt, climate change event occurred about 8,200 hundred years ago. This time Greenland temperatures dropped about 5 degrees a year. It caused “severe winters in Europe and some other areas caused glaciers to advance, rivers to freeze, and agricultural lands to be less productive.” “[S]evere winters in Europe and some other areas caused glaciers to advance, rivers to freeze, and agricultural lands to be less productive,” according to the Pentagon Report.

The most recent example of abrupt climate change began in the early 1300s, with effects that lasted until the mid-1800s. This event is known as “the Little Ice Age.” The Little Ice Age brought “severe winters, sudden climatic shifts, and profound agricultural, economic, and political impacts to Europe.” Although population density was a fraction of what it is today, “[f]amine, caused in part by the more severe climatic conditions, is reported to have caused tens of thousands of deaths between 1315 and 1319 alone.”

[i] Schwartz, P. and Randall, D., “An Abrupt Climate Change Scenario and Its Implications for United States National Security” (Oct. 2003)

The Pentagon Report, which found that abrupt climate change in the near future is “plausible,” although not probable, contains this chilling assessment:  “With inadequate preparation, the result could be a significant drop in the human carrying capacity of the Earth’s environment.”  The Pentagon Report, which will be discussed at length in another article, opined that, because of its extreme effects, abrupt climate change represented a greater national security threat than terrorism.