Climate Determinism Revisited: Multiple Equilibria in a Complex Climate Model

Citations Over TimeTop 10% of 2010 papers

Abstract

Abstract Multiple equilibria in a coupled ocean–atmosphere–sea ice general circulation model (GCM) of an aquaplanet with many degrees of freedom are studied. Three different stable states are found for exactly the same set of parameters and external forcings: a cold state in which a polar sea ice cap extends into the midlatitudes; a warm state, which is ice free; and a completely sea ice–covered “snowball” state. Although low-order energy balance models of the climate are known to exhibit intransitivity (i.e., more than one climate state for a given set of governing equations), the results reported here are the first to demonstrate that this is a property of a complex coupled climate model with a consistent set of equations representing the 3D dynamics of the ocean and atmosphere. The coupled model notably includes atmospheric synoptic systems, large-scale circulation of the ocean, a fully active hydrological cycle, sea ice, and a seasonal cycle. There are no flux adjustments, with the system being solely forced by incoming solar radiation at the top of the atmosphere. It is demonstrated that the multiple equilibria owe their existence to the presence of meridional structure in ocean heat transport: namely, a large heat transport out of the tropics and a relatively weak high-latitude transport. The associated large midlatitude convergence of ocean heat transport leads to a preferred latitude at which the sea ice edge can rest. The mechanism operates in two very different ocean circulation regimes, suggesting that the stabilization of the large ice cap could be a robust feature of the climate system. Finally, the role of ocean heat convergence in permitting multiple equilibria is further explored in simpler models: an atmospheric GCM coupled to a slab mixed layer ocean and an energy balance model.

Related Papers

• → Impact of sea ice floe size distribution on seasonal fragmentation and melt of Arctic sea ice(2020)88 cited
• → The Seasonal Ice Zone(1986)158 cited
• → Sources of sediment found in sea ice from the western Arctic Ocean, new insights into processes of entrainment and drift patterns(2003)133 cited
• → Role of ice dynamics in anomalous ice conditions in the Beaufort Sea during 2006 and 2007(2012)77 cited
• → Impact of floe size distribution on seasonal fragmentation and melt of Arctic sea ice(2019)11 cited