Clouds over Greenland
: The influence of clouds on contemporary and future Greenland Ice Sheet surface melt

  • Stefan Hofer

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The Greenland Ice Sheet (GrIS) has become the largest single mass contributor to global sea level. Since the mid-1990s the mass loss has been accelerating. The current consensus on the main drivers behind the shift in Greenland climate dynamics are: (1) A state change of the North Atlantic Oscillation towards an anticyclonic phase, (2) an above average temperature increase due to Arctic amplification and (3) an increase in absorbed shortwave radiation
due to the melt-albedo feedback.

However, thus far very few studies attempted to partition the GrIS surface energy budget (SEB) to find the main energy source behind the observed increase in surface melt. Furthermore, little is known about how much clouds have and will contribute to the recent and projected future GrIS melt increase.

In this thesis we find, that downwelling solar radiation has been the main driver of the recent changes in the SEB over the GrIS. Furthermore, we establish a connection between the observed increase in high-pressure frequency, an unreported reduction in summer cloud cover and the recent mass loss acceleration over the GrIS. Additionally, we also show that cloud microphysics are the leading source of uncertainties in future projections of GrIS melt.
Our analysis suggests that differences in cloud water phase distribution can add similar or larger uncertainties to projected Greenland melt than the choice of greenhouse gas emission scenario.

Because our analysis identifies a great sensitivity of the GrIS to cloud conditions, we mark three key areas to increase our ability to model the Greenland sea level rise contribution: (1) Increasing the amount of cloud (microphysical) observations in the Arctic. (2) Improving the representation of clouds in (regional) climate models. (3) Considering the dynamic nature of the Greenland cloud radiative effect and its transient response in a warming climate.
Date of Award23 Jan 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAndrew Tedstone (Supervisor) & Jonathan L Bamber (Supervisor)

Keywords

  • Greenland
  • Clouds
  • Climate
  • Climate Change
  • Microphysics
  • Sea level rise

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