Global Environment and Society Models

The general structure of an elementary global environment and society (GES) model designed for integrated assessment studies is illustrated in Fig. 1. The various interactions between the global environment, the socioeconomic system, and the policy makers are shown. These include both the direct physical coupling and the communication pathways that transform scientific knowledge and stakeholder positions via the media into public opinion and political action. A more disaggregated representation of the GES system, showing the breakdown into individual economic sectors and regions, with associated independent political decision makers, is shown in Fig. 2. The different economic sectors and regions are coupled in this case through the traditional mechanisms of trade as well as the global environment, which they jointly modify and by which they are individually affected.

For practical modeling applications, this multiactor breakdown of the GES system must still be strongly aggregated, as it is global biogeochemigal cycles /.V the climate system

Copyright ' 2001 liv Academic h: All rights ' ' reproduction in anv iornr reserved.

( lobal nvironment and ociety) model

INFORMATION PATHS

uj o

FIGURE 1 Physical interactions and communication pathways between the climate and environment, socioeconomic system, and policy in a coupled global environment and society (GES) model for integrated assessment studies.

impossible to realistically simulate the multitude of interacting players pursuing different goals in all sectors and regions of the global socioeconomic system. As in the analagous case of the climate system alone (which appears much simpler by comparison, however), insight into the dynamical behavior of the coupled GES system can be gained only iteratively, through the development of a hierarchy of different models, each of which highlights some particular features of the system and ignores other potentially important aspects.

The problem of managing the climate and environment system can be viewed as a general optimization problem: how should one deploy the finite resources available to humankind to achieve a sustainable development path that optimizes the human welfare of both the present and future generations? The task is to find an optimal balance between environmental protection efforts (in the forms of labor expenditures, human and capital investments, technological development, etc.) and the loss of welfare in other sectors relevant to human well-being (such as industrial development and the production of consumer goods, arising from the redeployment of the resources used to protect the environment from other economic activities).

In general, there will be no consensus on the definition of a single, overall world welfare function. Different political decision makers may have very different welfare concepts, which each will try to individually optimize. Thus the global optimization problem may be viewed as an intricate multiplayer game, including all the complexities of cooperative and noncooperative strategies, the creation of alliances, free-riding, direct and indirect agreement-enforcement mechanisms, etc.

However, in the following it will simply be assumed that an agreement has been reached through international negotiations on the form of the world welfare function one wishes to jointly optimize, so that the optimization task has been reduced to the

FIGURE 1 Physical interactions and communication pathways between the climate and environment, socioeconomic system, and policy in a coupled global environment and society (GES) model for integrated assessment studies.

Multi-actor integrated assessment model

\ POLICY

' *

CLIMATE AND ENVIRONMENTAL CHANGE ^

SOCIOECONOMIC

'-Ji.ty^-j.

A >

SYSTEM

<&

"^GREENHOUSE GAS EMISSIONS, DEFORESTATION, POLLUTION, ...

I?

FIGURE 2 Interactions between the climate, environment, socioeconomic system, and policy makers in a disaggregated, multiactor representation of the coupled global environment and society (GES) system of Figure 1.

FIGURE 2 Interactions between the climate, environment, socioeconomic system, and policy makers in a disaggregated, multiactor representation of the coupled global environment and society (GES) system of Figure 1.

determination of appropriate regulation policies that will lead to global greenhouse gas emmission paths that maximize the time-integrated world welfare. Thus we consider only the single-actor GES version of Fig. 1.

This is consistent in the sense that greenhouse warming, in contrast to other pollution problems, is essentially a global problem: because of the long lifetimes of greenhouse gases compared with their mixing times in the atmosphere, the distribution of greenhouse gases in the atmosphere is highly uniform, so that the geographical source of the emissions is irrelevant. Nevertheless, the treatment of climate management policy as a single-actor optimization problem presupposes an agreement on basic and controversial issues in the definition of the world welfare function. These include the values attached to nonmarket properties, such as health, life expectancy, the quality of the environment, or the diversity of species, and ethical issues such as intergenerational and interregional equity. Climate research or the natural sciences in general can clearly not resolve these issues within the framework of their own disciplines, but they can contribute from their reference level to an understanding of the interactions within the climate system and between the climate and socioeconomic system that are relevant in addressing the integrated climate policy problem.

A basic difficulty in the construction of a comprehensive GES model is the inherent complexity of each of the three subsystems indicated in Fig. 1. To obtain a manageable integrated model, the subsystems must be strongly simplified. By projecting the general multiactor game-theoretical problem onto the single-actor world welfare optimization problem, as discussed above, the complex "policy" subsystem has been effectively reduced for the present discussion to a single greenhouse-gas emissions regulator. However, for application in an integrated GES model, the state-of-the-art models of the remaining two subsystems must be similarly reduced.

Modern climate models are based on coupled general circulation models (GCMs) of the physical atmosphere-ocean system and three-dimensional geochemical cycle models of comparable complexity for the determination of the greenhouse gas concentrations. Both require very costly computer resources. Similarly, sophisticated state-of-the-art general equilibrium models (GEMS) of the global economy typically consider more than 100 interacting economic sectors and regions, compute large numbers of independent variables, and introduce many poorly determined empirical parameters. It is difficult to combine such models (particularly when they are developed in different coding languages) into a single, computationally efficient GES model with which one can systematically carry out a large number of exploratory simulations, such as sensitivity studies, cost-benefit analyses, and optimal control computations.

Thus, for application in integrated assessment studies, the existing state-of-the-art climate and socioeconomic subsystem models need to be replaced by computationally more efficient and analytically more transparent modules. In the following section it will be shown that this can be achieved for the climate subsystem by pro jecting the response properties of the climate system computed with a sophisticated three-dimensional climate model onto a dynamically equivalent impulse-response model. For the socioeconomic system, the long time-scales of the climate system require not only reductional simplifications of the standard GEM approach but also generalizations to include climate-change impacts, and, in addition, important long-term processes such as endogenous technological development, intergenerational transfers, and risk management. However, this will not be addressed here, and we shall consider later only a very simple economic model.

0 0

Post a comment