.. _recipes_wenzel16nat:

Legacy recipe: Projected land photosynthesis constrained by changes in the seasonal cycle of atmospheric CO\ :sub:`2`
=====================================================================================================================

.. note::

   This recipe has been retired and moved to the folder "archive". This recipe
   is only included for documentation purposes and not maintained any more. The
   last known ESMValTool version supporting this recipe is version 2.13.0.

Overview
--------

Selected figures from `Wenzel et al. (2016)`_ are reproduced with recipe_wenzel16nat.yml. Gross primary productivity (gpp) and atmospheric CO\ :sub:`2` concentrations at the surface  (co2s) are analyzed for the carbon cycle - concentration feedback in the historical (esmHistorical) and uncoupled (esmFixCLim1, here the carbon cycle is uncoupled to the climate response) simulations. The recipe includes a set of routines to diagnose the long-term carbon cycle - concentration feedback parameter (beta) from an ensemble of CMIP5 models and the observable change in the CO\ :sub:`2` seasonal cycle amplitude due to rising atmospheric CO\ :sub:`2` levels. As a key figure of this recipe, the diagnosed values from the models beta vs. the change in CO\ :sub:`2` amplitude are compared in a scatter plot constituting an emergent constraint.

.. _`Wenzel et al. (2016)`: https://www.nature.com/articles/nature19772

Available recipe and diagnostics
-----------------------------------

Recipes are stored in archive/legacy_recipes

    * recipe_wenzel16nat.yml

Diagnostics are stored in archive/legacy_diag_scripts/carbon_ec

    * carbon_beta: (1) scatter plot of annual gpp vs. annual CO\ :sub:`2` and
      (2) barchart of gpp(2xCO\ :sub:`2`)/gpp(1xCO\ :sub:`2`); calculates beta
      for emergent constraint (carbon_co2_cycle.ncl)
    * carbon_co2_cycle.ncl: (1) scatter plot of CO\ :sub:`2` amplitude vs.
      annual CO\ :sub:`2`, (2) barchart of sensitivity of CO\ :sub:`2` amplitude
      to CO\ :sub:`2`, (3) emergent constraint:
      gpp(2xCO\ :sub:`2`)/gpp(1xCO\ :sub:`2`) vs. sensitivity of CO\ :sub:`2`
      amplitude to CO\ :sub:`2`, (4) probability density function of constrained
      and unconstrained sensitivity of CO\ :sub:`2` amplitude to CO\ :sub:`2`


User settings
-------------

.. note::

   Make sure to run this recipe with the :ref:`configuration option
   <esmvalcore:config_options>` ``max_parallel_tasks: 1``.

#. Script carbon_beta.ncl

   *Required Settings (scripts)*

   * styleset: project style for lines, colors and symbols

   *Optional Settings (scripts)*

   * bc_xmax_year: end year to calculate beta (default: use last available year of all models)
   * bc_xmin_year: start year to calculate beta (default: use first available year of all models)

   *Required settings (variables)*

   none

   *Optional settings (variables)*

   none

#. Script carbon_co2_cycle.ncl

   *Required Settings (scripts)*

   * nc_infile: path of netCDF file containing beta (output from carbon_beta.ncl)
   * styleset: project style for lines, colors and symbols

   *Optional Settings (scripts)*

   * bc_xmax_year: end year (default = last year of all model datasets available)
   * bc_xmin_year: start year (default = first year of all model datasets available)

   *Required settings (variables)*

   * reference_dataset: name of reference dataset (observations)

   *Optional settings (variables)*

   none


Variables
---------

* co2s (atmos, monthly mean, plev longitude latitude time)
* gpp (land, monthly mean, longitude latitude time)


Observations and reformat scripts
---------------------------------

* ESRL: Earth System Research Laboratory, ground-based CO\ :sub:`2` measurements


References
----------

* Wenzel, S., Cox, P., Eyring, V. et al., 2016, Projected land photosynthesis constrained by changes in the seasonal cycle of atmospheric CO\ :sub:`2`. Nature 538, 499501, doi: doi.org/10.1038/nature19772


Example plots
-------------

.. figure:: /recipes/figures/wenzel16nat/fig_1.png
   :width: 12 cm
   :align: center

   Comparison of CO\ :sub:`2` seasonal amplitudes for CMIP5 historical simulations and observations showing annual mean atmospheric CO\ :sub:`2` versus the amplitudes of the CO\ :sub:`2` seasonal cycle at Pt. Barrow, Alaska (produced with carbon_co2_cycle.ncl, similar to Fig. 1a from Wenzel et al. (2016)).

.. figure:: /recipes/figures/wenzel16nat/fig_2.png
   :width: 12 cm
   :align: center

   Barchart showing the gradient of the linear correlations for the comparison of CO\ :sub:`2` seasonal amplitudes for CMIP5 historical for at Pt. Barrow, Alaska (produced with carbon_co2_cycle.ncl, similar to Fig. 1b from Wenzel et al. (2016)).

.. figure:: /recipes/figures/wenzel16nat/fig_3.png
   :width: 12 cm
   :align: center

   Emergent constraint on the relative increase of large-scale GPP for a doubling of CO\ :sub:`2`, showing the correlations between the sensitivity of the CO\ :sub:`2` amplitude to annual mean CO\ :sub:`2` increases at Pt. Barrow (x-axis) and the high-latitude (60N - 90N) CO\ :sub:`2` fertilization on GPP at 2xCO\ :sub:`2`. The red line shows the linear best fit of the regression together with the prediction error (orange shading), the gray shading shows the observed range (produced with carbon_co2_cycle.ncl, similar to Fig. 3a from Wenzel et al. (2016)).