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					CLM-CN update: Sensitivity to
   CO2, temperature, and
precipitation in C-only vs. C-N
             mode

   Peter Thornton, Jean-Francois
  Lamarque, Mariana Vertenstein,
    Nan Rosenbloom, Jeff Lee
          CLM-CN: Summary Model Structure and Fluxes

               Current                    Live          Live
                           Leaf
  Plant        Storage                    Stem       Coarse Root
  Pools
               Previous    Fine           Dead          Dead
               Storage     Root           Stem       Coarse Root



                                                 Wood Litter
                                                  (CWD)
   Litter
   Pools
               Litter 1       Litter 2             Litter 3
               (Labile)     (Cellulose)           (Lignin)


Soil Organic   SOM 1          SOM 2                SOM 3
Matter Pools   (fast)        (medium)              (slow)
           Atmospheric             Atmospheric
              CO2                   N species

                                                 Legend

                     Vegetation                   C flux

                      Biomass
                                                  N flux


                                                    Temp
                                                  sensitivity


                          Soil
                         Organic
                         Matter

             Coupled Carbon-Nitrogen dynamics
• Strong feedback between decomposition and plant growth:
soil mineral N is the primary source of N for plant growth.
• Can result in a shift from C source to C sink under warming.
                                                                P.E. Thornton, NCAR
CLM-CN spinup summary: global total C pools (CAM drivers)




           using accelerated decomposition method of Thornton and Rosenbloom, Ecol Mod (2005)
    GPP          transient, control   (transient-control)
 (CO2+Ndep)


offline CLM-CN
 (CAM drivers)




    coupled
(CAM – CLM-CN)
    NEE          transient, control   (transient-control)
 (CO2+Ndep)


offline CLM-CN
 (CAM drivers)




    coupled
(CAM – CLM-CN)
    TotC         transient, control   (transient-control)
 (CO2+Ndep)


offline CLM-CN
 (CAM drivers)




    coupled
(CAM – CLM-CN)
Cumulative land carbon uptake and net ecosystem exchange, 1850-2100
        with constant climate (25-yr cycle), prescribed [CO2]atm


                    Total C uptake (PgC)
                                                        Mean NEE (PgC/y)
                       (land fraction)
   Expt             1850-2000        2000-2100        1980-2000        2080-2100

   N dep              16 (6%)           50 (3%)            -0.24            -0.73

   CO2 fert           61 (22%)        220 (13%)            -0.98            -2.56

   CO2+Ndep           79 (29%)        301 (17%)            -1.31            -4.13

   CLM-C             223 (81%)        843 (49%)            -3.80           -10.75

           Land fractions referenced against cumulative fossil fuel emissions of
            276 PgC for 1850-2000 and 1732 PgC for 2000-2100 (SRES A2)
Land biosphere sensitivity to increasing atmospheric CO2 (L)


                                              CLM-C
                                              CLM-CN (CO2,Nfix,dep)
                                              CLM-CN (CO2,Nfix)
                                              CLM-CN (CO2)
                                          C4MIP models
                                          C4MIP mean


                                       Results from offline CLM-CN,
                                       driven with CAM climate, in
                                       carbon-only (CLM-C) and
                                       carbon-nitrogen (CLM-CN)
                                       mode, from present to 2100.
                                       Using SRES A2 scenario
                                       assumed CO2 concentrations.
Land biosphere sensitivity to increasing atmospheric CO2 (L)

                                              CLM-CN (CO2,Nfix,dep)
                                              CLM-CN (CO2,Nfix)
                                              CLM-CN (CO2)




                                       Evidence that increasing N-
                                       limitation under rising CO2 has
                                       an important effect on the
                                       transient behavior of L, and
                                       that consideration of
                                       anthropogenic N deposition
                                       reverses this trend by around
                                       2060.
NEE sensitivity to Tair and Prcp (interannual variability)

                                           5                                                       0




                                                                                                        NEE sensitivity to Prcp (PgC / mm d-1)
       NEE sensitivity to Tair (PgC / K)

                                           4                                                      -5



                                           3                       CLM-C                          -10
                                                                   CLM-CN


                                           2                                                      -15



                                           1                                                      -20



                                           0                                                      -25
                                                        Tair                      Prcp


                                           Coupling C-N cycles buffers the interannual variability of
                                           NEE due to variation in temperature and precipitation
                                           (global means, control simulations).
   NEE sensitivity to Tair and Prcp (CLM-CN vs CLM-C)

           Tair                          Prcp




CLM-CN                        CLM-CN




CLM-C                         CLM-C
 Components of NEE
 temperature response
                                NPP




                    NEE         HR




NPP dominates NEE response to
temperature in most regions.
Exceptions include Pacific
Northwest, Scandanavia.         FIRE
  Dissection of NPP
  temperature response
                                         GPP




                        NPP             Btran




Warmer temperatures lead to drying
in warm soils (increased evaporative
demand), and wetting in cold soils
(less soil water held as ice).         Soil ice
 Components of NEE
 precipitation response
                                NPP




                    NEE         HR




NPP dominates NEE response to
precipitation in tropics,
midlatitudes, HR dominates in
arctic and coldest climates.    FIRE
  Dissection of HR
  precipitation response
                                           HR




                       NEE             Snow depth




Higher Precip in arctic/cold climate
produces deeper snowpack, warmer
soils, increased HR.
                                          Tsoil
Potential for complex climate
feedbacks depending on the
spatial patterns of changing
temperature and precipitation.
NPP variability dominates the
Tair and Prcp response in most
locations, but HR dominates
the Prcp response in cold
climates, due to feedback
between snowpack, soil
warming, and enhanced HR.
NEE sensitivity to Tair and Prcp: effects of rising CO2 and
               anthropogenic N deposition
                                60


                                40
       % change from control




                                20


                                 0


                               -20
                                                        CLM-C: +CO2
                                                        CLM-CN: +CO2
                                                        CLM-CN: +CO2 +Nmin
                               -40

                                             Tair                        Prcp



                               Carbon-only model has increased sensitivity to Tair and
                               Prcp under rising CO2. CLM-CN has decreased sensitivity
                               to both Tair and Prcp, due to increasing N-limitation.
CLM-CN Summary: C-cycle response to nitrogen coupling,
         CO2, temperature, and precipitation
                                                                                                     5                                    0




                                                                                                                                                NEE sensitivity to Prcp (PgC / mm d-1)
             1.   Nitrogen coupling




                                                                 NEE sensitivity to Tair (PgC / K)
                                                                                                     4                                    -5
                  reduces sensitivity to
                  CO2. This effect
                                                                                                     3           CLM-C                    -10
                  increases with increasing                                                                      CLM-CN

                  CO2.                                                                               2                                    -15

             2.   Anthropogenic nitrogen
                                                                                                     1                                    -20
                  deposition alleviates this
                  effect.
                                                                                                     0                                    -25
                                                                                                          Tair                     Prcp
             3.   Nitrogen coupling
                  reduces global mean
                  sensitivity to temperature
                  and precipitation.
             4.   Complex spatial patterns
                  of NEE response to T
                                                                                                     60
                  and P. These responses
                  would be in tension                                                                40
                  under warmer-wetter

                                               % change from control
                  climate.                                                                           20


             5.   CO2 increases T and P                                                               0

                  sensitivities in carbon-
                  only model, decreases                                                          -20
                                                                                                                  CLM-C: +CO2
                                                                                                                  CLM-CN: +CO2
                  sensitivities in carbon-                                                                        CLM-CN: +CO2 +Nmin
                                                                                                 -40
                  nitrogen model.
                                                                                                          Tair                     Prcp
            CLM-CN summary contd:
    Nitrogen cycle buffers land carbon-
            climate feedbacks
               Nitrogen coupling…
•   reduces CO2 fertilization (reduces a
    negative feedback on climate system)
•   reduces T sensitivity (reduces a positive
    feedback)
•   reduces P sensitivity (uncertain feedback
    sign)
•   So, not a simple result with respect to total
    carbon-climate system gain.
    CLM-CN development path
• 3-pool vs 4-pool switch implemented and tested, with
  expected results.
• Landcover change effects (product pools) underway.
• 13C now incorporated and tested, transient runs
  underway, collaboration with CSU.
• Collaboration with LLNL to add 14C on the same
  framework.
• Implement age-class distributions.
• Introduce N speciation and direct effects of ozone on
  physiology, in collaboration with CCSM Chem-Climate
  WG.
Speciation of land N emissions



                             Nitrification vs.
                             denitrification depends
                             on aerobic state of soil,
                             probably at the
                             microscopic scale.
                             Sophisticated models
                             already exist, and it
                             should be possible to
                             adapt them for use in
                             CLM-CN.
                             Agricultural emissions
                             could be tied to new
                             efforts with crop
                             modeling.

				
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posted:2/5/2012
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