Patterns, processes, and impacts of abrupt climate change in a warm world: the past 11,700 years

Abrupt environmental changes punctuated the warm Holocene epoch (the past similar to 11,700 years), and studies of these episodes can provide insight into the dynamics that produce rapid climate changes, as well as their ecologic, hydrologic, and geomorphic impacts. This review considers the processes that generated warm world abrupt changes and their landscape and resource effects, including nonlinear climate system interactions, as well as the possibility that large climate variability can linearly produce apparent state shifts. Representative examples of Holocene changes illustrate processes that could produce future changes, including (1) rapid changes in ice sheets, such as by ca 8200 years before AD 1950, (2) shifts in the behavior of the El Nino-Southern Oscillation (e.g., at ca 5600 years before AD 1950) and Atlantic Meridional Overturning Circulation (e.g., at ca 2700 years before AD 1950), and (3) landatmosphere feedbacks, such as were possible in North Africa in the mid-Holocene. These case examples, drawn primarily from the Northern Hemisphere, also reveal the dynamics that generate the types of climate change impacts that would be particularly evident to individuals and societies, such as rapid tree species declines (observed to have taken place within as little time as 640 years) and persistent shifts in the regional availability of water. Holocene changes also demonstrate that even progressive climate change can produce important abrupt impacts; that increased rates of background climate forcing may increase the frequency of abrupt responses; and that impacts may well depend upon the particular sequence of changes. WIREs Clim Change 2012, 3:1943. doi: 10.1002/wcc.152