Interglacial Climate from Deglaciation to Glacial Inception
Thursday, 18 December 2014: 5:45 PM
Interglacials are the warm, minimum ice, high sea level end-member of the glacial climate cycles of the Pleistocene, with the present Holocene period as the most recent example. We have identified 11 interglacial intervals in the last 800 ka and have reviewed their occurrence, intensity, shape and timing, including the processes that accompany deglaciation and glacial inception. Our compilation of evidence from marine, terrestrial and ice core climate archives suggests that, despite spatial inhomogeneity, marine isotope stages (MIS) 5 and 11 were globally strong (warm), while MIS 13 tended to be cool. A step change in strength of interglacials at ~450 ka (mid-Brunhes) is apparent only in CO2, and Antarctic and deep ocean temperature. The onset of interglacials (deglaciation or glacial “termination”) is relatively rapid, and seems to require a combination of low orbital precession (high northern hemisphere summer insolation) and the existence of a large ice sheet. Terminations involve highly non-linear interactions of ocean and atmospheric dynamics, sea level, CO2 and temperature, along with the imposed external insolation forcing. The precise timing appears to be closely tied to the fall in precession but may be modulated by millennial scale climate variability that determines the pattern of change seen in temperature in each hemisphere. There is some organized variability and a range of climatic trends within interglacials, resulting in intensity maxima that may occur either early or late in different instances. The end of interglacials (glacial inception) is typically a slower process involving a global sequence of changes. Interglacials are typically 10-30 ka long. Proposed analogs do not easily inform us about the natural progression or length of the current interglacial, but due to a combination of reduced insolation variability and greenhouse gas concentrations the timing of the next glacial inception appears to be many tens of millennia in the future.