JP

Integrated earth systems modeling and the economics of the Kyoto Protocol

Many trace atmospheric constituents affect the radiative budget of the atmosphere. The Kyoto protocol includes carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), and sulfur hexafluoride (SF6). A variety of studies suggest that potential carbon sinks and opportunities to limit emissions of other greenhouse gases (GHGs) may reduce the cost of control. They also point to the risks of failing to control gases with very long lifetimes. Few studies have yet considered an integrated evaluation of the costs of multi-gas control strategies, or the implications of reductions in different mixes of GHGs on atmospheric composition, climate, and ecosystems. Using the MIT Integrated Global System Model (IGSM) as recently modified we examine multi-gas control as envisioned by the Kyoto protocol, exploring the costs of emissions reduction and the consequences for the atmosphere, climate, and ecosystems. The basic components of the IGSM are an Emissions Prediction and Policy Analysis (EPPA) model, a Natural Emissions Model, a coupled Atmospheric Chemistry and Climate Model, and a Terrestrial Ecosystems Model. We stop short of quantifying damages in monetary terms. Our ecosystem results illustrate tradeoffs that result from different control strategies. We find that inclusion of sinks and abatement opportunities for gases other than CO2 could reduce the cost of meeting the Kyoto agreement by 60 percent. Assuming the protocol is extended unchanged to 2100, we find little difference in climate and ecosystem effects between 2010 and 2100 for a strategy that achieves the required reduction with a multigas as compared to a CO2-only strategy. Under a more aggressive policy, increasing the reductions in Annex B countries and extending reductions to the rest of the world after 2010, significant differences in effects develop between the two strategies. This latter result indicates that 100-year GWPs as currently estimated fail to capture important time horizon and climate-chemistry interactive effects, and this failure can be significant for policy.

Integrated global system model (IGSM) for climate policy assessment: Feedbacks and sensitivity studies

Alternative policies to address global climate change are being debated in many nations and within the United Nations Framework Convention on Climate Change. To help provide objective and comprehensive analyses in support of this process, we have developed a model of the global climate system consisting of coupled sub-models of economic growth and associated emissions, natural fluxes, atmospheric chemistry, climate, and natural terrestrial ecosystems. The framework of this Integrated Global System Model is described and the results of sample runs and a sensitivity analysis are presented. This multi-component model addresses most of the major anthropogenic and natural processes involved in climate change and also is computationally efficient. As such, it can be used effectively to study parametric and structural uncertainty and to analyze the costs and impacts of many policy alternatives.

Initial runs of the model have helped to define and quantify a number of feedbacks among the sub-models, and to elucidate the geographical variations in several variables that are relevant to climate science and policy. The effect of changes in climate and atmospheric carbon dioxide levels on the uptake of carbon and emissions of methane and nitrous oxide by land ecosystems is one potentially important feedback which has been identified. The sensitivity analysis has enabled preliminary assessment of the effects of uncertainty in the economic, atmospheric chemistry, and climate sub-models as they influence critical model results such as predictions of temperature, sea level, rainfall, and ecosystem productivity. We conclude that uncertainty regarding economic growth, technological change, deep oceanic circulation, aerosol radiative forcing, and cloud processes are important influences on these outputs.

 

Integrated Global System Model for Climate Policy Analysis: I. Model Framework and Sensitivity Studies

Alternative policies to address global climate change are being debated in many nations and within the United Nations Framework Convention on Climate Change. To help provide objective and comprehensive analyses in support of this process, we have developed a model of the global climate system consisting of coupled sub-models of economic growth and associated emissions, natural fluxes, atmospheric chemistry, climate, and natural terrestrial ecosystems. The framework of the global system model is described and the results of sample first runs and a sensitivity analysis are presented. This multi- dimensional model addresses most of the major anthropogenic and natural processes involved in climate change and is also computationally efficient. As such, it can be used effectively to study parametric and structural uncertainty and to analyze the costs and impacts of many policy alternatives. The initial runs of the model have helped to define and quantify a number of feedbacks among the sub-models, and elucidate the geographical variations in many variables that are relevant to climate science and policy. The effect of changes in climate and atmospheric carbon dioxide levels on the uptake of carbon and emission of methane and nitrous oxide by land ecosystems, is a potentially important feedback which has been identified. The sensitivity analysis has enabled preliminary assessment of the effects of uncertainty in the economic, atmospheric chemistry, and climate sub-models as they influence critical model outputs like temperature, sea level, rainfall, and ecosystem productivity. We conclude that uncertainty regarding labor productivity, technological change, deep oceanic circulation, aerosol radiative forcing, and cloud processes are all important influences on these outputs. Subsequent papers will apply this global system model to assessment of policies currently under discussion in the Framework Convention on Climate Change and other issues such as impact-based methods for ranking greenhouse gases.

Integrated Global System Model for Climate Policy Assessment: Feedbacks and Sensitivity Studies

Alternative policies to address global climate change are being debated in many nations and within the United Nations Framework Convention on Climate Change. To help provide objective and comprehensive analyses in support of this process, we have developed a model of the global climate system consisting of coupled sub-models of economic growth and associated emissions, natural fluxes, atmospheric chemistry, climate, and natural terrestrial ecosystems. The framework of this Integrated Global System Model is described and the results of sample runs and a sensitivity analysis are presented. This multi-component model addresses most of the major anthropogenic and natural processes involved in climate change and also is computationally efficient. As such, it can be used effectively to study parametric and structural uncertainty and to analyze the costs and impacts of many policy alternatives.
        Initial runs of the model have helped to define and quantify a number of feedbacks among the sub-models, and to elucidate the geographical variations in several variables that are relevant to climate science and policy. The effect of changes in climate and atmospheric carbon dioxide levels on the uptake of carbon and emissions of methane and nitrous oxide by land ecosystems is one potentially important feedback which has been identified. The sensitivity analysis has enabled preliminary assessment of the effects of uncertainty in the economic, atmospheric chemistry, and climate sub-models as they influence critical model results such as predictions of temperature, sea level, rainfall, and ecosystem productivity. We conclude that uncertainty regarding economic growth, technological change, deep oceanic circulation, aerosol radiative forcing, and cloud processes are important influences on these outputs.

Interactions Among Emissions, Atmospheric Chemistry, and Climate Change: Implications for Future Trends

To gauge the overall effect of complex interactions among emissions, atmospheric chemistry, and climate, we have conducted a series of simulations on 120-year time scales, using a global coupled chemistry-climate model along with various predictions of anthropogenic emissions and different assumptions for chemistry and climate model parameters. To specifically identify the impacts of chemical species on climate change, we have also carried out sensitivity runs which include or exclude radiative effects due to increasing concentrations of greenhouse gases, and sulfate aerosols produced from anthropogenic sulfur emissions.
        Interactions among emissions, atmospheric chemistry, and climate are known to be complex. Based on current predictions of increasing future anthropogenic emissions, the climate will likely warm by some uncertain amount in the next century. The cooling effect caused by sulfate aerosols can offset a certain amount of this warming (about 20%, in our tests), but not the whole amount. It has been found that emissions of CH4, CO, NOx, and SO2 significantly influence the tropospheric concentrations of several important chemical species. Specifically, our simulations indicate that the average tropospheric OH concentration in the year 2100 will be 16-31% lower than its current level. As a result of this reduction, the predicted lifetimes of certain chemical species increase as we move into the next century. For example, in the year 2100 the lifetimes of CO and CH4 increase by 2 months and 2.5 years respectively from their current estimates. Also, we find that the overall influence of climatic variations on chemistry is less than that due to the increasing trends of emissions, especially for CH4.
        Climatic variations can still subtly impact many chemical patterns in the troposphere through changes in water vapor, temperature, rainfall, and cloud-cover patterns. However, predicted changes in climate do not reverse the overall trends of changing chemistry represented by the reduction in tropospheric OH concentration and related increases in the lifetimes of chemical species, which are driven primarily by the increasing emissions.

Interactive Chemistry and Climate Models in Global Change Studies

Continually increasing atmospheric concentrations of radiatively important chemical species such as CO2, CH4, N2O, tropospheric O3, and certain halocarbons most likely will cause future climate changes, which could in turn impact chemical reaction rates and thus lifetimes of many important chemical species. Complicated interactions between climate dynamics and atmospheric chemistry strongly suggest that a fully interactive, comprehensive chemistry-climate modeling system is needed to study the issue. This article reviews recent work in the new and challenging field of interactive chemistry-climate modeling, describing major efforts in model development and summarizing in detail applications of and results from these models.

Interannual Variability of Air-Sea Fluxes of Carbon Dioxide and Oxygen

The currently observed increase in atmospheric CO2 due anthropogenic emissions is substantially slowed by natural processes that incorporate CO2 into the terrestrial biota and the ocean. Year-to-year changes in the CO2 growth rate that exceed variations in the fossil fuel source indicate a significant variability in these global CO2 sinks. However, the enormous complexity of the terrestrial and oceanic biogeochemical systems that absorb atmospheric CO2 makes these sinks extremely difficult to understand and precisely quantify. Many techniques, including the interpretation of the relative changes in atmospheric CO2 and O2/N2, ocean modeling, and atmospheric data inversions, have been employed to estimate the mean and variability of global CO2 sinks. However, uncertainty remains large. The goal of this thesis is to improve understanding of global CO2 sinks by considering (1) the error in the atmospheric O2/N2 partitioning method due to the neglect of interannual variability in the air-sea fluxes of 02, and (2) the interannual variability of the ocean CO2 sink.
(cont.) A global, high-resolution ocean general circulation model is used to estimate the magnitude and understand the mechanisms of interannual variability in air-sea fluxes of both CO2 and 02. I find that the global variability in the fluxes of both gases are dominantly forced by large-scale physical processes governing upper ocean dynamics, particularly El Nifio / Southern Oscillation (ENSO) and, for 02, the North Atlantic Oscillation (NAO). Estimates of the extremes of CO2 and 02 flux variability for the period 1980-1998 are +/-0.5x1015 grams Carbon/yr (PgC/yr) and -70/+100x1012 mol/yr (Tmol/yr), respectively. Global 02 flux variability implies up to a 1.0 PgC/yr error in estimates of interannual variability in land and ocean CO2 sinks derived from atmospheric 02/N2 observations. This error is significant for estimates of annual sinks, but it is cumulatively negligible for estimates of mean sinks from October 1991 to April 1998. Increasing convergence of estimates of land.

Interhemispheric thermohaline circulation in a coupled box model

The interhemispheric thermohaline circulation is examined using Rooth's 3-box ocean model, whereby overturning strength is parameterized from density differencesbetween high-latitude boxes. Recent results with general circulation models indicate thatthis is a better analog of the Atlantic thermohaline circulation than a single-hemispherebox model. The results are compared with those of hemispheric box model studies, where possible, and the role of asymmetrical freshwater forcing is explored.
        Using both analytical and numerical methods, the linear and non-linear stability of the model is examined. Although freshwater forcing in the southern hemisphere alone governs overturning strength, increasing freshwater forcing in the northern hemisphere leads to a heretofore unrecognized instability in the northern sinking branch, due to an increasingly positive ocean salinity feedback. If the northern forcing is instead made weaker than the southern forcing, this feedback becomes negative. In contrast, the ocean salinity feedback is always positive in single-hemisphere models. Non-linear stability, as measured by the size of the perturbation necessary to induce a permanent transition to the southern sinking equilibrium, is also observed to depend similarly on the north:south forcing ratio.
      The model is augmented with explicit atmospheric eddy transport parameterizations, allowing examination of the eddy moisture transport (EMT) and eddy heat transport (EHT) feedbacks. As in the hemispheric model, the EMT feedback is always destabilizing, whereas the EHT may stabilize or destabilize. However, in this model whether the EHT stabilizes or destabilizes depends largely on the sign of the ocean salinity feedback and the size of the perturbation. Since oceanic heat transport in the southern hemisphere is weak, the northern hemisphere EMT and EHT feedbacks.

© 1999 American Meteorological Society

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