Congratulations to Rasmus Anker Pedersen – University of Copenhagen

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23 June 2016

Congratulations to Rasmus Anker Pedersen

Rasmus Anker Pedersen with the evaluation committee and supervisors. From left Peter Langen (supervisor, DMI), Pascale Braconnot (evaluation committee), Eigil Kaas (chairman of the evaluation committee), Rasmus Anker Pedersen, Bo Vinther (supervisor) and Masa Kageyama (evaluation committee).

Congratulations to Rasmus Anker Pedersen at Centre for Ice and Climate who succesfully defended his PhD thesis on Monday, June 20, 2016 and obtained the degree of Doctor of Philosophy.

In his Ph.D. project, Rasmus has used general circulation models to investigate if the past warm climate during the Eemian (125,000 years before present) can teach us anything about future climate change. The results reveal that the Eemian is not an ideal analogue for future climate; especially not for the melt on the Greenland ice sheet which is largely driven by the insolation anomaly. Changes in the Arctic sea ice cover are, however, central in shaping both the past and future climate change, and can affect the climate both within and beyond the Arctic region.

Rasmus will continue as postdoc at Centre for Ice and Climate, and will be working with climate and ice sheet modelling as part of the ice2ice project.

Title and abstract of the PhD thesis:

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.