| Summary: | The response to polar sea ice loss is separated, using dedicated coupled modelling experiments and multi-parameter pattern scaling, from the response to tropical warming and from general greenhouse warming. In the first chapter, the motivation for this work is presented with an overview of the existing literature and knowledge gaps. The second chapter presents a cross-comparison of the atmospheric near-surface sensitivity of two coupled models to Arctic sea ice loss and to low-latitude warming. The models agree well with more similarities found in the sensitivity to sea ice loss than to low-latitude warming. Warming and moistening of the Arctic, a dipole of sea level pressure between Eurasia and North America, and an equatorward shift in 850 hPa winds is found to scale with sea ice loss. In the third chapter, a larger pool of coupled experiments are used that largely confirm the results of the previous chapter. This chapter also covers the sensitivities of the zonal mean atmospheric circulation. Two-parameter pattern scaling of the surface ocean is carried out for the first time, and, unlike the atmosphere, the sensitivity to low-latitude warming is more robust than to sea ice loss. The subpolar North Atlantic is found to be a region of poor inter-model agreement due to complex dynamics and non-linearities, but qualitatively consistent signals can be found in response to sea ice loss; deep water formation decreases in the Labrador Sea and the meridional overturning circulation weakens. In the fourth chapter, the focus is expanded to include the impacts of Antarctic sea ice loss. New simulations are carried out to assess the response to sea ice loss in either hemisphere separately or coincidentally under different albedo parameter settings. Contrary to expectations, the response to Antarctic sea ice loss, mediated by tropical warming, is non-negligible in the Northern Hemisphere. With these new simulations, three-parameter pattern scaling is derived and we simultaneously compute the sensitivities to Arctic sea ice loss, Antarctic sea ice loss, and tropical warming, with a focus on the Northern Hemisphere's response. Finally in the fifth chapter, the results are summarized and remaining knowledge gaps are highlighted alongside suggestions for future work. Ph.D.
|
|---|