DOI: 10.5061/dryad.c59zw3rj0
title: Data from: Atmospheric feedbacks reverse the sensitivity of modeled photosynthesis to stomatal function

description: Stomata mediate fluxes of carbon and water between terrestrial plants and
 the atmosphere. These fluxes are governed by stomatal function and can be
 modulated in many Earth system models by an empirical parameter within the
 calculation of stomatal conductance, the stomatal slope (g1M).
 Intuitively, g1M represents the marginal water cost of carbon, relating it
 to the emergent plant property of water use efficiency. Observations show
 that g1M can range widely across and within plant types in varying
 environments, and this distribution of g1M is not captured within Earth
 system models which represent each plant type with a single g1M value.
 Here we examine how g1M influences photosynthesis using coupled Earth
 system model simulations by perturbing g1M to observed 5th and 95th
 percentiles for each plant type. We find that high g1M reduces
 photosynthesis nearly everywhere, while low g1M has regionally dependent
 responses. Under fixed atmospheric conditions, low g1M increases
 photosynthesis in the Amazon and central North America but decreases
 photosynthesis in boreal Canada. These responses reverse when the
 atmosphere responds interactively due to spatially differing sensitivity
 to increases in temperature and vapor pressure deficit. Choice of g1M also
 influences photosynthetic response to changes in
 atmospheric carbon dioxide (CO2), with lower and higher g1M
 modifying total global response to elevated 2x preindustrial CO2 by 6.4%
 and -9.6%, respectively. Our work demonstrates that atmospheric feedbacks
 are critical for determining the photosynthetic response to
 g1M assumptions and some regions are particularly sensitive to
 choice of g1M.
description: This dataset contains model output from simulations using the
 Community Earth System Model version 2 (CESM2; Danabasoglu et al., 2020),
 which is comprised of the Community Land Model 5 (CLM5; Lawrence et al.,
 2019), the Community Atmosphere Model 6 (CAM6; Bogenschutz et al., 2018),
 and a slab ocean based on output from the CESM2 Coupled Model
 Intercomparison Project Phase 6 (CMIP6; Danabasoglu & Gent, 2009)
 preindustrial control run.
description: # Data from: Atmospheric feedbacks reverse the sensitivity of modelled
 photosynthesis to stomatal function This repository contains climate
 simulation output from simulations run at 0.9x1.25° spatial resolution on
 the Community Earth System Model version 2 (CESM2; Danabasoglu et al.,
 2020), which is comprised of the Community Land Model 5 (CLM5; Lawrence et
 al., 2019), the Community Atmosphere Model 6 (CAM6; Bogenschutz et al.,
 2018), and a slab ocean based on output from the CESM2 Coupled Model
 Intercomparison Project Phase 6 (CMIP6; Danabasoglu & Gent, 2009)
 preindustrial control run. ## Description of the data and file structure
 This dataset is organized into zipped tarbells of the monthly timeseries
 output for our simulations. Each simulation has a `*_lnd.tar` for the land
 output and a `*_atm.tar` for the atmosphere output. Within each tarball,
 there is one netCDF file for each variable. Details about the simulations
 and variables are described further below. ``` SimulationA.tar.gz |-
 VariableA.nc |- VariableB.nc SimulationB.tar.gz |- VariableA.nc |-
 VariableB.nc ``` #### Climate model simulation output We present data from
 thirteen simulations run for 120 years at four different model
 configurations: * `coupled_*_SP_*` (Dynamic atmosphere and prescribed leaf
 area; Note that `SP` is at the end of the file name here) * `coupled_*`
 (Dynamic atmosphere and prognostic leaf area) * `landonly_SP_*`
 (Prescribed atmosphere and prescribed leaf area; Note that `SP` follows
 right after `landonly` here) * `landonly_*` (Prescribed atmosphere and
 prognostic leaf area) Configurations either had a dynamic or prescribed
 atmosphere and a prognostic (active biogeochemistry) or prescribed leaf
 area. Prescribed atmosphere and prescribed leaf area forcings were based
 on the output of the dynamic atmosphere and prognostic leaf area with
 default Medlyn slope parameter simulations. There are two fixed
 atmospheric CO~2~ concentrations for the dynamic atmosphere simulations: *
 `1xCO2` (1x preindustrial CO~2~ concentration; 284.7ppm) * `2xCO2` (2x
 preindustrial CO~2~ concentration; 569.4ppm) The prescribed atmosphere
 simulations were also run at both 1x and 2x preindustrial CO~2~, but in a
 slightly different naming convention: * `1xCO2CPL_1xCO2` (1x preindustrial
 CO~2~ concentration; 284.7ppm) * `2xCO2CPL_1xCO2` (2x preindustrial CO~2~
 concentration; 569.4ppm) There are three Medlyn slope parameter values: *
 `DEFmedslope` (default Medlyn slope used in CLM5) * `LOWmedslope` (5th
 percentile Medlyn slope based on Lin et al. 2015 dataset) * `HIGHmedslope`
 (95th percentile Medlyn slope based on Lin et al. 2015 dataset) We
 perturbed the Medlyn slope parameter by setting a minimum and maximum for
 each plant functional type based on the 5th and 95th percentile from Lin
 et al. (2015). In our analysis we compared the high and low Medlyn slope
 simulations against simulations with the default Medlyn slope parameter
 values used in CLM5. The default Medlyn slope values do not represent the
 mean or median of the observations we used for perturbations. Simulations
 with a dynamic atmosphere are named according to the convention
 `coupled_MedlynSlopeValue_atmCO2_LAI_Number` and simulations without a
 dynamic atmosphere are named according to the convention
 `landonly_LAI_MedlynSlopeValue_1xCO2CPL_1xCO2_Version`. Some dynamic
 atmosphere simulations are comprised of two simulations and denoted by the
 Number which, which will follow chronological order (e.g., `*_03` is the
 first half and `*_05` is the second half of `*` simulation). ####
 Variables  Each variable's netCDF file is named using an
 abbreviation. Abbreviated variable names can be mapped to full variable
 names in `var_key.csv`. The table below lists the variables analyzed in
 the Liu et al. (2025) manuscript that references this dataset, along with
 their abbreviation and units. Note that this table is a subset of the full
 list of variables. For a crosswalk between abbreviations and variable
 names for all other outputs, please reference the [CESM output variable
 directory](https://www.cesm.ucar.edu/community-projects/lens2/output-variables). Additional metadata about the variables are contained in the netCDF files.  | Variable Abbreviation | Variable Name | Units | | :-------------------- | :--------------------------------------------- | :-------------------- | | GPP | Gross primary production | gC/m^2^/s | | FPSN | Photosynthesis | µmol/m^2^/s | | FCTR | Canopy transpiration | W/m^2^ | | TLAI | Total leaf area | m^2^/m^2^ | | GSSUNLN | Sunlit leaf stomatal conductance at local noon | µmol H~2~O/m^2^/s | | IWUELN | Local noon intrinsic water use efficiency | µmol CO~2~/µmol H~2~O | | BTRANMN | Daily minimum of transpiration beta factor | unitless | | SOILLIQ | Soil liquid water | kg/m^2^ | | FSH | Sensible heat | W/m^2^ | | EFLX\_LH\_TOT | Total latent heat flux (+ to atm) | W/m^2^ | | FSDS | Atmospheric incident solar radiation | W/m^2^ | | TSA | 2m air temperature | K | | RAIN\_FROM\_ATM | Atmospheric rain | mm/s | | QBOT | Atmospheric specific humidity | kg/kg | | TBOT | Atmospheric air temperature | K | | PBOT | Atmospheric pressure at surface | Pa | 
 
 #### Code/Software The Community Earth System Model version 2 (CESM2) is
 open source and all code can be found on Github at
 [https://github.com/ESCOMP/CESM](https://github.com/ESCOMP/CESM). We thank
 all scientists, software engineers, and administration who contributed to
 CESM2's development.