Comparison between Holocene and Marine Isotope Stage-11 sea-level histories

The exceptionally long interglacial warm period known as Marine Isotope Stage 11 (MIS-11; 428-397 ky ago vs. ky vs. kyr) is often considered as a potential analogue for future climate development in the absence of human influence. We use a new high-resolution sea-level record-a globally integrated ice-volume signal-to compare MIS-11 and the current interglacial (Holocene). It is found that sea-level rise into both interglacials started over similar timescales relative to the respective insolation increases, and progressed up to - 50 m at similar rates of 1.0-1.2 m per century. Subsequent weak insolation changes anomalously prolonged the MIS-11 deglaciation over more than 20 ky. The main sea-level highstand was achieved at the second MIS-11 insolation maximum, with a timing closely equivalent to that of the Holocene highstand compared to its single insolation maximum. Consequently, while MIS-11 was an exceptionally long period of interglacial warmth, its ice-volume minimum/sea-level highstand lasted less than 10 ky, which is similar to the duration of other major interglacials. Comparison of the ends of MIS-11 and the Holocene based on timings relative to their respective maxima in mean 21 June insolation at 65°N suggests that the end of Holocene conditions might have been expected 2.0-2.5 ky ago. Instead, interglacial conditions have continued, with CO₂, temperature, and sea level remaining high or increasing. This apparent discrepancy highlights the need to consider that: (a) comparisons may need to focus on other orbital control indices, in which case the discrepancy can vanish; and/or (b) the feedback mechanisms that dominate the planetary energy balance may have become decoupled from insolation during the past 2 millennia.