OSCAR

A compact Earth system model.

How-to

Download a release. Read The Fine Manual.

OSCAR v3 is developed in Python 3.9 and run preferentially through IPython. It makes heavy use of the xarray package (v0.20.1), and netCDF4 for saving data (v1.5.7). It also relies on other common scientific packages: numpy (v1.23.3) and scipy (v1.9.3). Although the latest versions of the packages used to run OSCAR v3 are given, older versions are likely to work.

The source code is provided firstly for transparency, and only secondly for dissemination. This means that it is provided as is, and no support of any kind is guaranteed (but feel free to ask). Feedbacks and contributions are welcome.

Changelog

v3.3

• Updated: global temperature response parameters to those used in the IPCC AR6 WG1 Chapter 7, based on 35 CMIP6 Earth system models. Note that older parameters remain available.
• Updated: effective radiative forcing functions and parameters for long-lived greenhouse gases, also following the IPCC AR6 WG1 Chapter 7. This also implies update of the preindustrial atmospheric concentrations of these gases.
• Changed: internal solving and saving algorithm to output mid-year average values (instead of end-of-year). Now, to be able to start-up a simulation from an initial state that is the end of another's, one must set the call argument get_final=True to request a second output that is the final state of the called simulation.
• Fixed: internal summation of anthropogenic and biomass-burning emissions in mod_process that could lead to NaN values under some uncommon combination of regional aggregations and land carbon cycle parameterizations.

v3.2

• Added: regional aggregation options following the MESSAGE integrated assessment model's 11 regions.
• Added: ODR calibration functions (based on scipy.odr), to be used for future module calibrations.
• Improved: ocean carbon cycle, with a reworked formulation and structural parameters based on Bern-SCM, and a new option for the pCO2 functional form.
• Improved: time-stepping and solving. This includes an auto-initialization of the state variables, and a semi-automatic adjustment of the number of substeps based on the value of D_CO2. The latter can be turned off using adapt_nt=False when calling the model.
• Removed: the wrapper function (that was mostly confusing and had limited functionality).
• Fixed: the values of x_OH_NOX, x_OH_CO and x_OH_VOC when mod_Foh_fct == log. The sensitivity of the OH sink to ozone precursors would be of the opposite sign in half the parameterizations.
• Fixed: an error in the formulation of p_shift in the bookkeeping module. It would previously overwrite some minor transitions with NaN, leading to a slight underestimation of land-use change emissions.
• Fixed: math display in MANUAL.

v3.1.2

• Added: finest possible regional aggregation, given that the parameters are still calibrated following the v2 approach.
• Added: an additional option for the structure of the bookkeping module, in which the effect of land cover change and management are separated. This is added in a temporary file that will be merged with fct_process_alt in the next version.
• Fixed: the definition of Houghton_2017 regions that had Colombia and Guinea swapped. This had minimal impact on the land C cycle.

v3.1.1

This version is exactly the one used in the IPCC AR6. A number of functionalities were added, mostly for convenience.

• WARNING: fct_process was renamed mod_process for consistency, which may affect existing run scripts.
• Added: options in fct_process_alt to alter the structure of the bookkeeping module. The default structure is now defined over only one bio_land dimension instead of two (bio_from and bio_to) to reduce the model's memory demand. Mathematically, this is equivalent to the full structure, although extremely small differences can be seen because of the numerical solving. This can be tested using the provided check_LUC_structure script.
• Added: an option to add a constant shift and/or some noise to the Monte Carlo parameters, through the new adjust_config function in fct_genMC.
• Added: the e_ohu parameter representing the ocean heat uptake efficacy in the climate module (see e.g. here). For consistency, this parameter is set to one by default for all configurations.
• Added: new metrics (D_Flasc, d_CO2, CFF, d_OHC) in mod_process to help diagnose the model ex-post.
• Added: new regional aggregations consistent with the IPCC AR6.
• Added: the get_IPCC_AR6_parameters script, to generate a set of prior parameters identical to those used in the IPCC AR6.

v3.1

• Improved: land carbon cycle, exactly as described by Gasser et al. (2020). This comes with a recalibration of the module's preindustrial steady-state on TRENDYv7 models.
• Changed: the formulation of D_ewet (wetlands areal emissions), to account for the new flexible structure of the land carbon cycle. This reduces the speed at which CH₄ emissions respond to a change in net primary productivity.

v3.0.1

• Fixed: an error in the formula of the function describing the overlap of absorption bands between CH₄ and N₂O, causing significantly wrong RFs. This error appeared during the conversion from v2 to v3, however, and it did not affect the earlier versions of the model.

v3.0

The physical equations and parameter values of this version are exactly the same as in v2.4. A few notable changes are worth mentioning here.

• Added: an option to choose the solving scheme of the differential system. The default solving scheme is now an Eulerian exponential integrator (that typically requires fewer sub-timesteps to be stable).
• Removed: the possibility of recalibrating the model's parameters on-the-fly, and especially the regional aggregation of the land carbon cycle. For now, calibrated parameters are directly imported from OSCAR v2, but this feature will be progressively re-implemented has v3 is developed further and new calibrating data become available.
• Changed: the global temperature 2-box model's formulation, to correspond to a more usual formulation found in climate science. This is purely esthetic; this does not change the projected global temperature.
• Changed: the structure of the bookkeeping module for land-use emissions. Specifically, the initialisation is now coded like any other carbon cycle flux. This does not significantly alter the module's performance.

v3

This is a complete revamp of OSCAR, for which the code was rewritten from scratch and moved to Python 3. OSCAR v3 relies heavily on the xarray package (and therefore netCDF saving format), to better structure the input and output data, to more easily deal with the many dimensions of internal data, and to parallelize simulations so that the run time of a typical Monte Carlo ensemble has been significantly reduced. It also uses its own object classes (Model and Process) that make it easy to change, extend or tune the model's structure and/or equations. Because of this complete overhaul, manipulation of the model has to be learned from scratch, however.

v2.4

This version is the last update of OSCAR v2. It is meant to be as close to OSCAR v3.0 as possible.

• Added: the mod_biomeV3 option to force biome aggregation to that of v3.0.
• Added: the mod_EHWPspeed option that introduces further variations in the decay time of harvested wood products. In addition to the normal configuration, the fast one scales the value of tau_HWP so that 20% of the pool remains after 80% of the initial decay time (a rescale by ~0.5), and the slow one scales the value of tau_HWP so that 30% of the pool remains after 150% of the initial decay time (a rescale by ~1.25).
• Removed: the mod_EHWPfct option, so that only exponential decay of harvested wood products is now possible. This slightly increases CO₂ emissions from land-use change in a Monte Carlo run.
• Removed: the dependency of p_wet on the mod_LSNKcover option. It is now the average of all possible configurations, which has very little effect on the simulated wetlands CH₄ emissions.

v2.3.1

• Added: a new parameter p_HWP1_BB quantifying how much of the harvested wood products in pool 1 are actually burnt in the open, and thus accounted for in non-CO₂ anthropogenic biomass burning emissions. It is set to 0.5 to roughly match present-day estimates.
• Added: a new configuration based on GISS-E2-R-TOMAS to the mod_O3Tradeff option.
• Removed: the Laube-HL configuration of the mod_O3Sfracrel option, since it makes little physical sense to have parameters specific to high latitudes in a global model like OSCAR.
• Removed: the Daniel2010-lin configuration of the mod_O3Snitrous option, since a non-saturating effect of N₂O onto stratospheric O₃ lacked physical ground.
• Fixed: the discretization of r_HWP (the response function for harvested wood products). The previous discretization caused delayed and therefore too low emissions.
• Fixed: the value of k_BC_adjust for the option mod_BCadjust == CSIRO. This has very little impact on a Monte Carlo run.
• Fixed: the value of radeff_O3t for the option mod_O3Tradeff == mean_ACCMIP. This has no impact on a Monte Carlo run.
• Fixed: the default values of the beta_npp0 and CO2_comp parameters when isolating the urban biome, to prevent NaN from appearing during the simulation.
• Fixed: NaN values no longer appear in the alpha_BB parameters when isolating the urban biome.

v2.3

• Added: permafrost carbon thaw and release, exactly as described by Gasser et al. (2018). This comes with a new CO₂ atmospheric flux accounting for the oxidation of geologic CH₄ released in the atmosphere.

v2.2.2

• Fixed: an error in the pre-processing of the AeroChem_ACCMIP input data for the CSIRO-Mk360 configuration. This was causing biased atmospheric lifetimes for POA and BC aerosols under this configuration (and slightly biased ones under the average mean-ACCMIP configuration).

v2.2.1

• Fixed: an error in the f_pCO2 functions, causing a too efficient ocean carbon sink under high warming and high atmospheric CO₂.
• Fixed: an error in the f_pH function, causing unrealistic surface ocean pH changes.

v2.2

Initial release on GitHub. Exact model used by Gasser et al. (2017).

References

v3.1 (partial) | Gasser, T., L. Crepin, Y. Quilcaille, R. A. Houghton, P. Ciais & M. Obersteiner. "Historical CO₂ emissions from land-use and land-cover change and their uncertainty." Biogeosciences 17: 4075–4101 (2020). doi:10.5194/bg-17-4075-2020

v2.3 (partial) | Gasser, T., M. Kechiar, P. Ciais, E. J. Burke, T. Kleinen, D. Zhu, Y. Huang, A. Ekici & M. Obersteiner. "Path-dependent reductions in CO₂ emission budgets caused by permafrost carbon release." Nature Geoscience 11: 830-835 (2018). doi:10.1038/s41561-018-0227-0

v2.2 (full) | Gasser, T., P. Ciais, O. Boucher, Y. Quilcaille, M. Tortora, L. Bopp & D. Hauglustaine. "The compact Earth system model OSCAR v2.2: description and first results." Geoscientific Model Development 10: 271-319 (2017). doi:10.5194/gmd-10-271-2017