### Abstract

The strengths of future carbon dioxide (CO_{2}) sinks are highly uncertain. A sound methodology to characterize current and predictive uncertainties in carbon cycle models is crucial for the design of efficient carbon management strategies. We demonstrate such a methodology, Markov Chain Monte Carlo (MCMC), by performing a Bayesian calibration of a simple global-scale carbon cycle model with historical carbon cycle observations to (1) estimate probability density functions (PDFs) of key carbon cycle parameters, (2) derive statistically sound probabilistic predictions of future CO_{2} sinks, and (3) assess the utility of hypothetical observation systems to reduce prediction uncertainties. We find that the PDFs of model parameter estimates are not normally distributed, and the residuals show statistically significant temporal autocorrelation. The assumption of normally distributed PDFs likely causes biased results, and the neglect of autocorrelation in the residual of the annual CO_{2} time series causes overconfidence in parameter estimates and predictions. Using interannually varying global temperature observations as forcing provides important information: terrestrial parameter PDFs are shifted and are more sharply constrained when compared to PDFs estimated when forcing the carbon cycle with a simple energy-balance model. Although CO_{2} observations provide a strong constraint on the total carbon sink, adding independent observations of terrestrial and oceanic fluxes has the potential to reduce uncertainty in predictions of this total sink more rapidly. Assimilating hypothetical annual observations of terrestrial and oceanic CO_{2} fluxes with realistic uncertainties reduces predictive uncertainties about CO_{2} sinks in the year 2050 by as much as a factor of 2 compared to assimilating CO_{2} concentrations alone.

Original language | English (US) |
---|---|

Article number | GB2030 |

Journal | Global Biogeochemical Cycles |

Volume | 22 |

Issue number | 2 |

DOIs | |

State | Published - Jun 1 2008 |

### Fingerprint

### All Science Journal Classification (ASJC) codes

- Global and Planetary Change
- Environmental Chemistry
- Environmental Science(all)
- Atmospheric Science

### Cite this

}

**A Bayesian calibration of a simple carbon cycle model : The role of observations in estimating and reducing uncertainty.** / Ricciuto, Daniel M.; Davis, Kenneth J.; Keller, Klaus.

Research output: Contribution to journal › Article

TY - JOUR

T1 - A Bayesian calibration of a simple carbon cycle model

T2 - The role of observations in estimating and reducing uncertainty

AU - Ricciuto, Daniel M.

AU - Davis, Kenneth J.

AU - Keller, Klaus

PY - 2008/6/1

Y1 - 2008/6/1

N2 - The strengths of future carbon dioxide (CO2) sinks are highly uncertain. A sound methodology to characterize current and predictive uncertainties in carbon cycle models is crucial for the design of efficient carbon management strategies. We demonstrate such a methodology, Markov Chain Monte Carlo (MCMC), by performing a Bayesian calibration of a simple global-scale carbon cycle model with historical carbon cycle observations to (1) estimate probability density functions (PDFs) of key carbon cycle parameters, (2) derive statistically sound probabilistic predictions of future CO2 sinks, and (3) assess the utility of hypothetical observation systems to reduce prediction uncertainties. We find that the PDFs of model parameter estimates are not normally distributed, and the residuals show statistically significant temporal autocorrelation. The assumption of normally distributed PDFs likely causes biased results, and the neglect of autocorrelation in the residual of the annual CO2 time series causes overconfidence in parameter estimates and predictions. Using interannually varying global temperature observations as forcing provides important information: terrestrial parameter PDFs are shifted and are more sharply constrained when compared to PDFs estimated when forcing the carbon cycle with a simple energy-balance model. Although CO2 observations provide a strong constraint on the total carbon sink, adding independent observations of terrestrial and oceanic fluxes has the potential to reduce uncertainty in predictions of this total sink more rapidly. Assimilating hypothetical annual observations of terrestrial and oceanic CO2 fluxes with realistic uncertainties reduces predictive uncertainties about CO2 sinks in the year 2050 by as much as a factor of 2 compared to assimilating CO2 concentrations alone.

AB - The strengths of future carbon dioxide (CO2) sinks are highly uncertain. A sound methodology to characterize current and predictive uncertainties in carbon cycle models is crucial for the design of efficient carbon management strategies. We demonstrate such a methodology, Markov Chain Monte Carlo (MCMC), by performing a Bayesian calibration of a simple global-scale carbon cycle model with historical carbon cycle observations to (1) estimate probability density functions (PDFs) of key carbon cycle parameters, (2) derive statistically sound probabilistic predictions of future CO2 sinks, and (3) assess the utility of hypothetical observation systems to reduce prediction uncertainties. We find that the PDFs of model parameter estimates are not normally distributed, and the residuals show statistically significant temporal autocorrelation. The assumption of normally distributed PDFs likely causes biased results, and the neglect of autocorrelation in the residual of the annual CO2 time series causes overconfidence in parameter estimates and predictions. Using interannually varying global temperature observations as forcing provides important information: terrestrial parameter PDFs are shifted and are more sharply constrained when compared to PDFs estimated when forcing the carbon cycle with a simple energy-balance model. Although CO2 observations provide a strong constraint on the total carbon sink, adding independent observations of terrestrial and oceanic fluxes has the potential to reduce uncertainty in predictions of this total sink more rapidly. Assimilating hypothetical annual observations of terrestrial and oceanic CO2 fluxes with realistic uncertainties reduces predictive uncertainties about CO2 sinks in the year 2050 by as much as a factor of 2 compared to assimilating CO2 concentrations alone.

UR - http://www.scopus.com/inward/record.url?scp=50849107004&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=50849107004&partnerID=8YFLogxK

U2 - 10.1029/2006GB002908

DO - 10.1029/2006GB002908

M3 - Article

AN - SCOPUS:50849107004

VL - 22

JO - Global Biogeochemical Cycles

JF - Global Biogeochemical Cycles

SN - 0886-6236

IS - 2

M1 - GB2030

ER -