ľ¹Ï¸£ÀûÓ°ÊÓ

The atmosphere and ocean are two strongly interacting components in the climate system. The atmospheric forcing is the fast component and is modelled as noise, i.e. as a high-frequency random process; the ocean reacts to this forcing and exhibits long time scale variability.

The research in this thesis focuses on the effect of atmospheric noise on the ocean variability, concerning (i) sea-level variability and (ii) the stability of the Atlantic Meridional Ocean Circulation (AMOC), which is the result of a complex system of currents in the Atlantic Ocean. In particular, an appropriate null hypothesis is formulated for sea-level variability, which allows to distinguish specific phenomena in the ocean circulation (e.g. El Niño) from the background signal driven by the atmospheric forcing.

Atmospheric noise, such as fluctuations in the amount of freshwater input in the North Atlantic, can induce transition behaviour of the ocean circulation. This is particularly alarming for the AMOC, which is responsible for the relatively mild climate of north-western Europe, compared to maritime regions at similar latitudes on the Pacific.

In this work, the likelihood of a noise-induced collapse of the present-day AMOC is studied, both in a conceptual climate model and in state-of-the-art global climate models, such as the ones used in the fifth assessment report of the Intergovernmental Panel for Climate Change (IPCC).