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.