All interglacials are different, but some are more different than others

Examination of the palaeoclimate record of the last 800 kyr has revealed a large diversity among interglacials in terms of their duration, structure and intensity.  Interglacials may be classified as either short (mean duration 13 kyr) or long (mean duration 28 kyr).  The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks: the longest interglacials are characterized by the obliquity peak lagging the first precession minimum by 10±2 kyr and leading the second precession minimum by a similar amount; thus the first boreal summer insolation minimum occurs at the time of maximum obliquity, which overrides the increase in precession and prevents glacial inception associated with a decline in summer insolation.  The phasing of precession and obliquity also determines the structure of an interglacial, leading to two main categories: (1) shorter interglacials characterized by rapid deglaciation and an early temperature optimum, usually followed by a decline; and (2) longer interglacials characterized by protracted deglaciation and the persistence of interglacial values over two insolation peaks, with the interglacial peak occurring in the second insolation maximum.  With respect to intensity, a broad feature is that interglacials before the Mid-Brunhes Event (MBE; 430 ka) appear weaker (cooler, higher δ¹⁸O_benthic, atmospheric CO₂ lower than pre-industrial concentrations).  The strongest interglacials occurred after the MBE, although MIS7e and MIS7c-a are closer in intensity to pre-MBE interglacials.  Of particular interest is MIS 11c, one of the most unusual Quaternary interglacials.  Its features include: (i) a high sea-level highstand attained under modest insolation forcing; (ii) a long duration extending over two insolation peaks; (iii) persistence of relatively stable atmospheric CO₂ concentrations, remaining in the range 270-282 ppm for a 24 kyr period; and (iv) a decoupling between high CO₂ and high sea level in the early part of the interglacial that is unique in the last 800 kyr.  Although some of these features are also encountered in other interglacials, their combination with strong interglacial intensity is unique to MIS 11c and appears to be a function of the high CO₂concentrations from the beginning of the interglacial.