Reconciling uncertainties in integrated science and policy models: Applications to global climate change

Uncertainties are endemic to science and policy models of global climate change. Although it is impossible to make accurate predictions of future socio-economic outcomes, characterizing the relevant scientific and economic uncertainties could provide important insights for policy. Integrated assessments provide the platform for analyzing the role of these uncertainties. In this thesis tools of data reconciliation are used to integrate available information into scientific and policy models of greenhouse gases. The role of uncertainties in scientific and policy models of global climate change is examined, and implications for global change policy are drawn.; Methane is the second most important greenhouse gas. Global sources and sinks of methane have significant uncertainties. A chance constrained methodology was developed and used to perform inversions on the global methane cycle. Budgets of methane that are consistent with source fluxes, isotopic and ice core measurements were determined. While it is not possible to come up with a single budget for CH{dollar}sb4{dollar} performing the calculation with a number of sets of assumed priors suggests a convergence in the allowed range for sources. In some cases--wetlands (70-130 Tg/yr), rice paddies (60-125 Tg/yr) a significant reduction in the uncertainty of the source estimate is achieved. Our results compare favorably with the most recent measurements of flux estimates. The approach also constrains fossil CH{dollar}sb4{dollar} flux estimates as well as other anthropogenic emissions from biomass burning and landfills. For comparison. a similar analysis using Bayes Monte Carlo simulation was performed.; The question of the missing sink for carbon remains unresolved. Two analyses that attempt to quantify the missing sink were performed. First, a steady state analysis of the carbon cycle was used to determine the pre-industrial inter-hemispheric carbon concentration gradient. The analysis shows that the value of the missing sink could be reduced by 0.6 GT/yr, although that number depends critically on the covariance between seasonality of the carbon concentration and seasonality of atmospheric transport. Second, a full blown dynamic inversion of the carbon cycle was performed. An advection diffusion ocean model with surface chemistry, coupled to box models of the atmosphere and the biosphere was inverted to fit available measurements of {dollar}sp{lcub}12{rcub}{dollar}C and {dollar}sp{lcub}14{rcub}{dollar}C carbon isotopes using differential-algebraic optimization. The biospheric uptake inferred from the calibrated dynamic mode of the carbon cycle is about 1.9 GT/yr for 1990. This implies a net oceanic uptake of 2.2 GT/yr. The model effectively suggests that the "missing" sink for carbon is hiding in the biosphere. These results are in fair agreement with a number of recent estimates of the biospheric uptake. The inferred biospheric uptake trajectory for the past 200 years indicates that the biosphere has been responsible for almost as much uptake of atmospheric carbon as the oceans.; Comprehensive control strategies would be facilitated by the formulation of indices that allow for an evaluation of tradeoffs between greenhouse gases. An optimal control formulation was set up to determine values for such indices that incorporate the scientific and economic aspects of the greenhouse gas abatement. Scenario dependent truce gas indices were calculated for CH{dollar}sb4{dollar}, N{dollar}sb2{dollar}O, HCFC-22. Trace gas indices were found to be far more sensitive to the level of non-linearity in the greenhouse damages than to costs of abatement. The indices were also found to be reasonably robust over a wide range of possible outcomes of energy supply futures but depended critically on the choice of a discount rate. In the case of methane, scientific and economic uncertainties can cause the value of the index to vary by a factor of three.