Editing IPCC:AR6/WGI/Chapter-5 (section)

==== 5.4.5.1 Evaluation of the Contemporary Carbon Cycle in Concentration-driven Runs ====

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To give confidence in their projections, models need to be compared to the widest possible array of observational benchmarks. This is particularly the case for highly uncertain land carbon cycle feedbacks ( [[#Arora--2013|Arora et al., 2013]] ; [[#Friedlingstein--2014b|Friedlingstein et al., 2014b]] ). Land models within ESMs can be compared to multiple different datasets that test different aspects of the models. These include fluxes, such as gross carbon uptake, and states, such as leaf area and carbon stocks, which influence carbon fluxes and are diagnostic of carbon turnover times. Comparisons can also be made between between carbon and water cycles and other aspects of the terrestrial carbon cycle. To provide these multiple orthogonal constraints, a model benchmarking system – the international land model benchmarking (ILAMB) – has been developed ( [[#Collier--2018|Collier et al., 2018]] ).

Figure 5.22 shows an overview set of land (Figure 5.22a) and ocean (Figure 5.22b) benchmarks applied to both the CMIP5 and CMIP6 historical simulations. There is good evidence of an improvement in model performance from CMIP5 (in yellow) to CMIP6 (in green), in both the land and ocean, based on these benchmarks. The mean of the CMIP6 land models outperforms or performs equivalently to the mean of the CMIP5 land models on all available metrics.

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[[File:f34fe91fc558c40f0269ddc8c1522426 IPCC_AR6_WGI_Figure_5_22.png]]

'''Figure 5.22 |''' '''Overview scores for CMIP5 (left-hand side of table) and CMIP6 (right-hand side of table) Earth system models (ESMs), for multiple benchmarks against different datasets.''' '''(a)''' Benchmarking of ESM land models; '''(b)''' benchmarking of ocean models. Scores are relative to other models within each benchmark row, with positive scores indicating a better agreement with observations. Models included are only those from institutions that participated in both CMIP5 and CMIP6 carbon cycle experiments, in order to trace changes from one ensemble to the next. CMIP5 models are labels in blue and CMIP6 in red. Further details on data sources and processing are available in the chapter data table (Table 5.SM.6).

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'''Table 5.4 |''' '''Properties of the CMIP6 Earth system models (ESMs), focusing on the land and ocean carbon cycle components of these models''' '''''(Ar''''' or '''''a''''' '''''et''''' ''a'' l., 2020). Characteristics listed under each ESM are: number of vegetation carbon pools (veg C pools); number of soil and litter carbon pools (dead C pools); number of Plant Functional Types (PFTs); whether wildfire is represented (fire); whether vegetation dynamics is represented (dynamic veg); whether permafrost carbon is represented (permafrost C); whether the nitrogen cycle is represented (nitrogen cycle); the number of phytoplankton types (phytoplankton); the number of zooplankton types (zooplankton); and the list of ocean nutrients represented (limiting nutrients).

{| class="wikitable"
|-
! Modelling Group

! CSIRO

! BCC

! CCCma

! CESM

! CNRM

! GFDL

! IPSL

! JAMSTEC

! MPI

! NorESM2-LM

! UK

|-
| '''ESM'''

| ACCESS-ESM1.5

| BCC-CSM2-MR

| CanESM5

| CESM2

| CNRM-ESM2-1

| GFDL-ESM4

| IPSL-CM6A-LR

| MIROC-ES2L

| MPI-ESM1.2-LR

| NorESM2-LM

| UKESM1-0-LL

|-
| colspan="12"| '''Land carbon/biogeochemistry component'''

|-
| '''Model name'''

| CABLE2.4

CASA-CNP

| BCC-AVIM2

| CLASS-CTEM

| CLM5

| ISBA-CTRIP

| LM4p1

| ORCHIDEE ( 2)

| MATSIRO (phys)

VISIT-e (BGC)

| JSBACH3.2

| CLM5

| JULES-ES-1.0

|-
| '''Veg C pools'''

| 3

| 3

| 3

| 22

| 6

| 6

| 8

| 3

| 3

| 3

| 3

|-
| '''Dead C pools'''

| 6

| 8

| 2

| 7

| 7

| 4

| 3

| 6

| 18

| 7

| 4

|-
| '''PFTS'''

| 13

| 16

| 9

| 22

| 16

| 6

| 15

| 13

| 12

| 21

| 13

|-
| '''Fire'''

| No

| No

| No

| Yes

| Yes

| Yes

| No

| No

| Yes

| Yes

| No

|-
| '''Dynamic Veg'''

| No

| No

| No

| No

| No

| Yes

| No

| No

| Yes

| No

| Yes

|-
| '''Permafrost C'''

| No

| No

| No

| Yes

| No

| No

| No

| No

| No

| Yes

| No

|-
| '''Nitrogen cycle'''

| Yes

| No

| No

| Yes

| No

| No

| No

| Yes

| Yes

| Yes

| Yes

|-
| colspan="12"| '''Ocean carbon/biogeochemistry component'''

|-
| '''Model name'''

| WOMBAT

| MOM4_L40

| CMOC (biol)

| MARBL

| PISCESv2-gas

| COBALTv2

| PISCES-v2

| OECO2

| HAMOCC6

| HAMOCC5.1

| MEDUSA-2.1

|-
| '''Phytoplankton'''

| 1

| 0

| 1

| 3

| 2

| 3

| 2

| 2

| 2

| 1

| 2

|-
| '''Zooplankton'''

| 1

| 0

| 1

| 1

| 2

| 3

| 2

| 1

| 1

| 1

| 2

|-
| '''Limiting nutrients'''

| P, Fe

| P

| N

| N, P, Si, Fe

| N, P, Si, Fe

| N, P, Si, Fe

| N, P, Si, Fe

| N, P, Fe

| N, P, Si, FE

| N, P, Si, Fe

| N, Si, Fe

|}

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