Reply on RC2

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Dansgaard-Oeschger (D-O) events, millennial-scale climate oscillations between stadial and interstadial conditions (of up to 10&ndash;15 &deg;C in amplitude at high northern latitudes), occurred throughout the Marine Isotope Stage 3 (MIS3; 27.8&ndash;59.4 ka) period. The climate modelling community up to now has not been able to answer the question: Are our climate models too stable to simulate D-O events? To address this, this manuscript lays the ground-work for a MIS3 D-O protocol for general circulation models which are used in the International Panel for Climate Change (IPCC) assessments. We review: D-O terminology, community progress on simulating D-O events in these IPCC-class models (processes and published examples), and evidence about the boundary conditions under which D-O events occur. We find that no model exhibits D-O like behaviour under pre-industrial conditions. Some, but not all, models exhibit D-O like oscillations under MIS3 and/or full glacial conditions. Greenhouse gases and ice-sheet configurations are crucial. However most models have not run simulations of long enough duration to be sure which models show D-O like behaviour, under either MIS3 or full glacial states. We propose a MIS3 baseline protocol at 38 ky (38 to 32 ky) period, which (1) shows a regular sequence of D-O events, and (2) features the intermediate ice-sheet configuration and medium-to-low MIS3 greenhouse gas values which our review suggests are most conducive to D-O like behaviour in models. We also provide a protocol for a second "kicked Heinrich meltwater" experiment, since previous work suggests that this variant may be helpful in preconditioning a state in models which is conducive to D-O events. This review and protocol is intended to provide modelling groups investigating MIS3 D-O oscillations with a common framework.