Climate and Environmental Physics (CEP)

Earth System Modelling: Biogeochemical Cycles

Models

Carbon modelling has been pioneered by Ulrich Siegenthaler and Hans Oeschger at CEP in the 1970ies. Projections of atmospheric CO₂ with the “Bern model” were instrumental in the first Assessments by the Intergovernmental Panel on Climate Change and for the legally-binding metric to compare emissions of different greenhouse gases in the Kyoto Protocol.

Since the development of the early reduced-form, box-diffusion model, the numerical model hierarchy and the range of applications has been continuously expanded.

The following models are currently used by the group and developed and applied in collaboration with the groups at CEP and in national and international collaborations.

Bern3D-LPX

The Bern3D-LPX is a cost-efficient Earth System Model of Intermediate Complexity. It is designed to perform transient simulations on glacial-to-interglacial timescales and probabilistic simulations with many ensemble members. It is run on the Linux clusters of the division and of the University. It links the Bern3D model and the LPX-DGVM.

Bern3D

The Bern3D model couples a 3-dimensional, geostrophic-frictional balance dynamic ocean circulation model, a 2-dimensional energy balance model of the atmosphere, and modules for the cycling of carbon and related tracers, marine ecosystems, and a marine sediment diagenesis module. Bern3D simulates exchange fluxes between atmosphere and ocean of heat, water, CO₂, carbon isotopes, N₂O, oxygen, CFCs and noble gases. It represents the marine cycle of dissolved and particulate organic matter, opal, calcite and aragonite and related flows through reactive ocean sediments and exchange with the lithosphere. It explicitly represents a broad range of water mass, ventilation time scales, and biogeochemical tracers such as temperature, salinity, chlorofluorocarbons, radiocarbon and stable carbon isotopes, phosphate, dissolved organic and inorganic carbon, silica, oxygen, alkalinity, iron, isotopes of neodymium, protactinium and thorium. It may also be coupled to a marine ecosystem model (PISCES model).

Transient Simulation of the Past 450,000 Years (Copyright by S. Ritz)

LPX-DGVM

The LPX-DGVM, the Land surface Processes and eXchanges Dynamic Global Vegetation Model, is an off-spring of the Lund-Potsdam-Jena DGVM family. It describes land biosphere-atmosphere exchange of carbon and water, the cycling of carbon and nitrogen through the and biosphere, and vegetation distribution on individual grid cells. The LPX-Bern version features within a coherent numerical setup different land classes per grid cell, including natural forest and grassland, peatland, wetland, cropland, pasture, and urban areas. The distribution of wetland and peatland area may be simulated dynamically and shifting cultivation is explicitly represented in the land use module. Vegetation is represented by land class-specific plant functional types. Plant and snow cover determine land surface albedo. The model simulates land sources and sinks of CO₂, CH₄, and N₂O, the carbon and nitrogen inventories of major reservoirs such as peat, mineral and permafrost soils, litter, wood and leaves, the flow and stocks of carbon isotopes (¹²C , ¹³C, ¹⁴C), and the oxygen isotope signatures (¹⁸O) of plant water and tree-ring cellulose.

CESM

The Community Earth System Model (CESM) is a state-of-the-art Earth system model developed by
the National Centre for Atmospheric Research, Boulder, USA. It is run by CEP at the Swiss National
Supercomputing Centre. CESM permits us to study Earth System variability and change (CESM) in a
detailed spatially and temporally resolved setting.

We also apply highly cost-efficient reduced form models such as the HILDA box-diffusion ocean model and Impulse Response Function (IRF) representations of complex models.