Constraining the strength of the terrestrial CO<sub>2</sub> fertilization effect in the Canadian Earth system model version 4.2 (CanESM4.2)
Earth system models (ESMs) explicitly simulate the interactions between the physical climate system components and biogeochemical cycles. Physical and biogeochemical aspects of ESMs are routinely compared against their observation-based counterparts to assess model performance and to evaluate how th...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-07-01
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| Series: | Geoscientific Model Development |
| Online Access: | http://www.geosci-model-dev.net/9/2357/2016/gmd-9-2357-2016.pdf |
| Summary: | Earth system models (ESMs) explicitly simulate the interactions between the
physical climate system components and biogeochemical cycles. Physical and
biogeochemical aspects of ESMs are routinely compared against their
observation-based counterparts to assess model performance and to evaluate
how this performance is affected by ongoing model development. Here, we
assess the performance of version 4.2 of the Canadian Earth system model
against four land carbon-cycle-focused, observation-based determinants of
the global carbon cycle and the historical global carbon budget over the
1850–2005 period. Our objective is to constrain the strength of the
terrestrial CO<sub>2</sub> fertilization effect, which is known to be the most
uncertain of all carbon-cycle feedbacks. The observation-based determinants
include (1) globally averaged atmospheric CO<sub>2</sub> concentration,
(2) cumulative atmosphere–land CO<sub>2</sub> flux, (3) atmosphere–land CO<sub>2</sub>
flux for the decades of 1960s, 1970s, 1980s, 1990s, and 2000s, and (4) the
amplitude of the globally averaged annual CO<sub>2</sub> cycle and its increase
over the 1980 to 2005 period. The optimal simulation that satisfies
constraints imposed by the first three determinants yields a net primary productivity (NPP) increase from ∼ 58 Pg C year<sup>−1</sup> in 1850 to
about ∼ 74 Pg C year<sup>−1</sup> in 2005; an increase of ∼ 27 %
over the 1850–2005 period. The simulated loss in the global soil carbon
amount due to anthropogenic land use change (LUC) over the historical period is
also broadly consistent with empirical estimates. Yet, it remains possible
that these determinants of the global carbon cycle are insufficient to
adequately constrain the historical carbon budget, and consequently the
strength of terrestrial CO<sub>2</sub> fertilization effect as it is represented in
the model, given the large uncertainty associated with LUC emissions over the
historical period. |
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| ISSN: | 1991-959X 1991-9603 |