01 July 2019

Congratulations to Ida Margrethe Ringgaard

Ida Ringgaard with Assessment Committee and Supervisors. From left: Eigil Kaas, Anders Svensson, Jens Hesselbjerg Christensen, Ida Ringgaard, Gunilla Svensson, Timo Vihma and Shuting Yang.

Congratulations to Ida Margrethe Ringgaard at Physics of Ice, Climate and Earth who successfully defended her PhD thesis Friday 28 June 2019, and obtained the degree of Doctor of Philosophy.

Title and abstract of PhD thesis:

Title: Sensitivity of Arctic sea ice change on climate in the coupled climate model EC-Earth

Abstract:

The climate system has throughout time been sensitive to changes in the Arctic sea ice. During the last glacial period, the climate experienced abrupt climatic changes (Dansgaard-Oeschger events), likely due to a rapid retreat of the Nordic Seas sea ice. Present climate experiences a sea ice loss as well, where the regional sea ice loss in the Barents-Kara Seas has been linked to cold European winters. In the future, Arctic sea ice is projected to disappear. This PhD project aimed at investigating the sensitivity of the climate to changes in the Arctic sea ice. For this, the atmosphere-ocean coupled climate model EC-Earth was used. Focus was on the impact of the regional sea ice loss in the Barents-Kara Seas, as well as the pan-Arctic sea ice loss projected in the RCP8.5 emission scenario. Testing the sensitivity to sea ice changes in a coupled climate model required a method for constraining sea ice. Two methods using the surface sensible heat flux to nudge sea ice were tested, one of them conserving energy. This latter method required a fine balance to avoid model instabilities, a balance that we did not succeed in finding for longer simulations. Our results showed that Barents-Kara sea ice loss might be linked to a cooling over parts of Europe in winter, but the response was weak and only present for the temporal mean winter temperatures. The coldest winters did not show a statistically significant cooling over Europe for any amount of sea ice loss in the Barents-Kara Seas. The RCP8.5 scenario simulation was run for 1350 years (1850-3200) using EC-Earth-PISM, where EC-Earth is coupled to an interactive Greenland Ice Sheet. During the simulation, the Arctic transitioned from having a perennial sea ice cover to an ice-free Arctic Ocean. The overall evolution of the RCP8.5 simulation resembled that of the CMIP5 ensemble, although the loss of the Arctic sea ice appeared to lead to a shift in trends for some key parameters: the precipitation variability increased, the AMOC stabilized after an initial reduction and the Arctic Ocean stratification strengthened. However, as changes in sea ice coincided with increasing global temperature and anthropogenic Greenhouse Gas emissions, more work is required to separate the effects.