 |
| Titel |
Controls on terrestrial carbon feedbacks by productivity versus turnover in the CMIP5 Earth System Models |
| VerfasserIn |
C. D. Koven, J. Q. Chambers, K. Georgiou, R. Knox, R. Negrón-Juárez, W. J. Riley, V. K. Arora, V. Brovkin, P. Friedlingstein, C. D. Jones |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 17 ; Nr. 12, no. 17 (2015-09-07), S.5211-5228 |
| Datensatznummer |
250118085
|
| Publikation (Nr.) |
 copernicus.org/bg-12-5211-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| To better understand sources of uncertainty in projections of terrestrial
carbon cycle feedbacks, we present an approach to separate the controls on
modeled carbon changes. We separate carbon changes into four categories using a
linearized, equilibrium approach: those arising from changed inputs
(productivity-driven changes), and outputs (turnover-driven changes), of both
the live and dead carbon pools. Using Coupled Model Intercomparison Project
Phase 5 (CMIP5) simulations for five models, we find that changes to the live
pools are primarily explained by productivity-driven changes, with only one
model showing large compensating changes to live carbon turnover times. For
dead carbon pools, the situation is more complex as all models predict a
large reduction in turnover times in response to increases in productivity.
This response arises from the common representation of a broad spectrum of
decomposition turnover times via a multi-pool approach, in which
flux-weighted turnover times are faster than mass-weighted turnover times.
This leads to a shift in the distribution of carbon among dead pools in
response to changes in inputs, and therefore a transient but long-lived
reduction in turnover times. Since this behavior, a reduction in inferred
turnover times resulting from an increase in inputs, is superficially similar
to priming processes, but occurring without the mechanisms responsible for
priming, we call the phenomenon "false priming", and show that it masks much
of the intrinsic changes to dead carbon turnover times as a result of
changing climate. These patterns hold across the fully coupled,
biogeochemically coupled, and radiatively coupled 1 % yr−1 increasing CO2
experiments. We disaggregate inter-model uncertainty in the
globally integrated equilibrium carbon responses to initial turnover times,
initial productivity, fractional changes in turnover, and fractional changes
in productivity. For both the live and dead carbon pools, inter-model spread
in carbon changes arising from initial conditions is dominated by model
disagreement on turnover times, whereas inter-model spread in carbon changes
from fractional changes to these terms is dominated by model disagreement on
changes to productivity in response to both warming and CO2 fertilization.
However, the lack of changing turnover time control on carbon responses, for
both live and dead carbon pools, in response to the imposed forcings may
arise from a common lack of process representation behind changing turnover
times (e.g., allocation and mortality for live carbon; permafrost, microbial
dynamics, and mineral stabilization for dead carbon), rather than a true
estimate of the importance of these processes. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|