A suite of early Eocene (~ 55 Ma) climate model boundary conditions

Abstract

Abstract. We describe a set of early Eocene (~ 55 Ma) climate model boundary conditions constructed in a self-consistent reference frame and incorporating recent data and methodologies. Given the growing need for uniform experimental design within the Eocene climate modelling community and the challenges faced in simulating the prominent features of Eocene climate, we make publicly available our data sets of Eocene topography, bathymetry, tidal dissipation, vegetation, aerosol distributions and river runoff. Major improvements in our boundary conditions over previous efforts include the implementation of the ANTscape palaeotopography of Antarctica, more accurate representations of the Drake Passage and Tasman Gateway, as well as an approximation of sub grid cell topographic variability. Our boundary conditions also include for the first time modelled estimates of Eocene aerosol distributions and tidal dissipation, both consistent with our palaeotopography and palaeobathymetry. The resolution of our data sets is unprecedented and will facilitate high resolution climate simulations. In light of the inherent uncertainties involved in reconstructing global boundary conditions for past time periods these data sets should be considered as one interpretation of the available data and users are encouraged to modify them according to their needs and interpretations. This paper marks the beginning of a process for reconstructing a set of accurate, open-access Eocene boundary conditions for use in climate models.

Climate sensitivity and meridional overturning circulation in the late Eocene using GFDL CM2.1

“…A comparison of proxy data with the model SSTs for the 400, 800 and 1600 ppm experiments is shown in Figure 8 using GPlates, reconstructed to an age of 38 Ma using the Paleomagnetic reference frame of Torsvik et al (2012) and van Hinsbergen et al (2015). This ensures consistency with the model boundary conditions (Baatsen et al, 2016).…”

“…This relocation map was determined by a downslope relocation algorithm from the model topography. Aerosol forcing was taken from the Eocene (55 Ma) reconstruction of Herold et al (2014), and adapted to our model's input types.…”

Deep time evidence for climate sensitivity increase with warming

“…From these, we can glean that pre-PETM MAT was~10°C warmer than PI [Huber and Caballero, 2011;Lunt et al, 2012;Zachos et al, 2008]. Much of this extra warmth may derive from albedo reduction from much reduced high-latitude ice and snow, complemented by low-latitude, albedo reductions from reduced subtropical landmass [Herold et al, 2014] ( Figure S1) and increased land vegetation cover [Huber and Caballero, 2011]. Aerosol decrease and higher minor greenhouse gas concentrations may have each enhanced warming by~1°C [Lunt et al, 2012].…”

Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

“…The results presented in this paper include two cases, one with low (2x pre-industrial CO 2 and CH 4 ) and another with high (4x pre-industrial CO 2 and CH 4 ) greenhouse gas concentrations. CH 4 are increased with the same factor, in order to represent middle-late Eocene estimates (Beerling et al, 2009(Beerling et al, , 2011Herold et al, 2014). …”

“…Most recent modelling studies focussed on reconstructing either early Eocene extreme (Huber and Caballero,65 2011; Lunt et al, 2012;Herold et al, 2014) or the latest Eocene -early Oligocene (Hill et al, 2013;Ladant et al, 2014;Kennedy et al, 2015) conditions. Both proxies and especially model results are relatively scarce for the middle-late Eocene considered here (Bartonian and Priabonian ∼41.2-…”