Study of Man’s Impact on Climate (Matthews et al., 1971) and a comprehensive scientific study conference on climate (GPS No. 16, 1975) that was organized by the Joint Organizing Committee for GARP and sponsored by the World Meteorological Organization, the International Council of Scientific Unions, and the United Nations Environment Program. The conclusions of these bodies generally coalesce about the following points:
Climate modeling seems to be the most clearly promising path.
We are fortunately already well along the way as a result of scientific initiatives of two decades ago, but models are still too simple to answer subtle questions.
One can identify many if not most of the missing pieces of the jigsaw puzzle.
New observational data are required to inspire, advance, and verify improved models.
There is a need for technological innovation, faster computers, and possibly new institutions.
It will be useful to consider the physical basis for climate modeling, to expose some critical problems impeding model development, particularly those relevant to energy utilization, and to show some results of a recent simulation experiment as a vehicle for discussing common misconceptions.
An exposition of the elements that enter into a comprehensive climate model is treated at length elsewhere (Smagorinsky, 1974). Our present purpose is to outline briefly the degree to which we are presently capable of modeling each of these physical processes (see Figure 9.1).
The most extensive experience lies with modeling the large-scale three-dimensional hydrothermodynamics of the global atmosphere. Although constant improvement is still being achieved, it is no longer a critical factor in general circulation modeling. Smaller-scale convective transfer, although a current subject of concentrated research activity, is well enough at hand in general circulation models that simulations with such models of the long-term dispersive characteristics of inert tracers in the atmosphere show reasonable correspondence with observation (Mahlman, 1973). Radiative-transfer theory for a given distribution of the radiatively active constituents carbon dioxide, ozone, and water vapor seems to be adequate. However, arbitrary distributions of clouds and other aerosols still cannot be dealt with in full generality.
The elements of the hydrologic cycle have been modeled with moderate success. The ability to predict the atmospheric water-vapor distribution seems to be sufficient for calculating infrared radiative absorption (the greenhouse effect) but not for determining the formation of clouds. Simple engineering parameterizations seem almost adequate for determining continental water storage, that is, soil moisture. Also, an ability to model variations in continent al snow cover gives a reasonable first approximation. This is particularly important in determining changes in surface reflectivity (albedo).
The oceans play a key role in virtually all questions of climatic interest. Coupled ocean-atmosphere models are still in a crude state of development since their first construction in the mid-1960’s. An understanding of the mechanisms governing sea-ice variations and how this alters the transmission of heat between ocean and atmosphere is still to be adequately modeled.
As indicated above, an ability to predict the cloud stage with adequate precision to determine the radiative consequences remains one of the most difficult problems in climatic modeling.
The above elements are all essential to a model presumably capable of assessing the sensitivity of climate to thermal pollution. Furthermore, if one wishes to assess the consequences of other industrial effluents, that is, particulates and carbon dioxide, additional elements are required to be determined by models. The CO2 buffering mechanisms in the ocean and biosphere are not yet fully understood. More-