Synthesis and Assessment Product (SAP) 3.4: Abrupt Climate Change

This report is one in a series of 21 SAPs produced between 2004 and 2009 by the U.S. Climate Change Science Program, aimed at providing current assessments of climate change science in the U.S. to inform public debate, policy, and operational decisions. This report considers progress in understanding four abrupt changes in the paleoclimatic record whose impacts are so rapid and large that they would pose clear risks to society if they were to recur: 1) rapid change in glaciers, ice sheets, and hence sea level; 2) widespread and sustained changes to the hydrologic cycle; 3) abrupt change in the northward flow of warm, salty water in the upper layers of the Atlantic Ocean associated with the Atlantic Meridional Overturning Circulation (AMOC) and southward flow of cold water in the deep Atlantic; and 4) rapid release to the atmosphere of methane trapped in permafrost and on continental margins.

This report reviews the progress in the understanding of patterns and mechanisms of past abrupt climate change in the ocean and on land, as well as new observations revealing unanticipated rapid dynamic changes of modern glaciers, ice sheets, and ice shelves and the processes that are contributing to these changes.  A summary and explanation of the main results is presented first, followed by an overview of the types of abrupt climate change considered in this report. The subsequent chapters then address each of these types of abrupt climate change, including a synthesis of the current state of knowledge and an assessment of the likelihood that one of these abrupt changes may occur in response to human influences on the climate system.

Publication Date: December 2008

Authors or Affiliated Users:

  • Peter U. Clark
  • Andrew J. Weaver
  • Edward Brook
  • Edward R. Cook
  • Thomas L. Delworth
  • Konrad Steffen

Related Organizations:


  • Oceans

Resource Category:

Resource Types:

  • Assessment
  • Climate science


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