PhD defence by Rasmus A. Pedersen

Modelling interglacial climate – investigating the mechanisms of a warming climate

ABSTRACT Past warm climate states could potentially provide information on future global warming. The past warming was driven by changed insolation rather than an increased greenhouse effect, and thus the warm climate states are expected to be different. Nonetheless, the response of the climate system involves some of the same mechanisms in the two climate states. This thesis aims to investigate these mechanisms through climate model experiments. This two-part study has a special focus on the Arctic region, and the main paleoclimate experiments are supplemented by idealized experiments detailing the impact of a changing sea ice cover.

The first part focusses on the last interglacial climate (125,000 years before present) which was characterized by substantial warming at high northern latitudes due to an increased insolation during summer. The simulations reveal that the oceanic changes dominate the response at high northern latitudes, while the direct insolation impact is more dominant in the tropics. On Greenland, the simulated warming is low compared to the ice core reconstructions. Surface mass balance calculations indicate that the oceanic conditions favor increased accumulation in the southeast, while the insolation appears to be the dominant cause of the expected ice sheet reduction.
The second part explores the atmospheric sensitivity to the location of sea ice loss. Three investigated sea ice scenarios with ice loss in different regions all exhibit substantial near-surface warming, with maximum warming occurring in winter. The three scenarios all affect the climate beyond the Arctic, especially the mid-latitude circulation which is sensitive to the location of the ice loss.

Together, the results presented in this thesis illustrate that the changes in the Arctic sea ice cover are important for shaping both past and future warm climate states. Nonetheless, the last interglacial is not an ideal analogue for future climate changes, as the changed insolation has a large impact – especially on the Greenland ice sheet.

Vejledere: Bo M. Vinther, NBI og Peter L. Langen, DMI

If interested please contact Rasmus Anker Pedersen for a copy of the thesis - anker