Arctic sea ice and bifurcations in a hierarchy of simplemodels (tentative)

In my PhD I will look at the question of what bifurcations exist in the Arctic sea ice system and what processes control them. My project will in particular focus on the role seasonality plays in bifurcations and look at bifurcations in both summer and perennial sea ice.Outside of academic literature bifurcations are commonly called 'tipping points' and refer to points in a system where a small variation of a control parameter leads to an abrupt shift in the qualitative behaviour of a system.The climate of the Arctic is primarily driven by solar radiation, and due to its high albedo sea ice greatly impacts the energy input to the Arctic. Further effects include the formation of surface temperature inversions, thermal shielding of the ocean and impacts on local atmospheric circulation(Liu et al., 2016). Growth and melt of sea ice can also affect global atmospheric and ocean circulation(Semmler et al., 2016). Sea ice is also vital for Arctic ecology - it provides a habitat for many animals, and its growth and melt cycles play an important role in circulating nutrients in the oceans. As such, study into transitions in and out of states with summer and perennial sea ice is of great interest due to the large impacts they have both on the Arctic and wider world. Moreover, Arctic sea ice decline is a common measure for the progress of climate change so it is of interest to improve understanding of its progression.My project will look at a hierarchy of models to identify which conditions models predict bifurcations in Arctic sea ice in. I will focus on bifurcations controlled by changing of atmospheric CO2concentrations. This will help improve the understanding of the likelihood of a bifurcation looming in the near future, but more importantly will clarify how different components of Arctic climate interact in models of increasing complexity. Better conceptual models of how sea ice behaves under forcing will also help provide new benchmarks for sea ice representation in GCMs.I also hope to look beyond the near future and consider the existence of bifurcations under other forcing situations - in particular under orbital forcing during glacial-interglacial cycles.