The level of complexity of these issues meant that it was not until the development of digital computers in the 1950s that any serious attempt could be made to model the atmosphere as a whole. Early attempts treated the atmosphere and, indeed, the Earth's surface, as homogeneous composites of all possible values of the variables employed. Hence, there was little or no differentiation between land and sea or among the various layers of the atmosphere. Clearly, no model based on these initial conditions would be able to represent the complexity of the overall model.

The development of computer power has, on a rapidly accelerating trajectory, improved the accuracy of existing models and enabled integrating new variables into the overall model. As the model grows in its ability to provide satisfactory answers—that is, to provide increasingly better predictive power in forecasting actual weather conditions—scientists are able to identify new variables that may be included. On some occasions, practical issues preclude direct observation of the desired variables and, hence, proxy variables must be included instead. At the same time, researchers are adjusting their models by employing different variable weightings, varying certain initial conditions, and making other slight changes to determine the sensitivity of the models and their ability to replicate accurate simulations on a consistent basis.

No individual model is likely to provide a definitive answer, or to be qualitatively better than any other or to have one set of weightings that is consistently superior to any other. Prudence suggests, therefore, that researchers will search for a broad consensus of results before making claims for improved performance. This is facilitated by the peer-reviewing process in the academic world, which measures research findings against existing knowledge and information. The process tends to enhance accuracy, but delays reporting of some findings and tends to make researchers act with more equivocation than they might be asked to show by journalists or politicians. As the issues of global atmospheric warming and attendant climate change have taken an increasingly central role in political agendas around the world, climate modelers have found their methods and results questioned more stringently than ever before and there have, as a result, been some cross-cultural collisions that have done little, if anything, to improve aggregate understanding.

One of the first scientists successfully to make the link between the emission of carbon dioxide into the atmosphere at unprecedented rates with future climate change, was Syukuro Manabe. Manabe integrated oceanic and atmospheric climate models and identified the flows between them of momentum, heat, and water. His conclusion was that general atmospheric temperatures would rise by several degrees if the amount of carbon dioxide in the atmosphere doubled. A great deal of subsequent work on circulation models has been involved with either verifying or falsifying this initial conclusion. The main effect has been to refine the result and it has become apparent that, despite many (often well-financed) attempts to find flaws in the fundamental assumptions of such models, there can be no meaningful doubt that increasing levels of carbon dioxide

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and other greenhouse gases are having a measurable impact on current weather conditions and will have a greater impact in the future. The issue has been complicated for political reasons as powerful incentives exist to inspire certain people and interests to cast doubt on the findings. Media ownership issues in countries such as the United States mean that proper treatment of science in public discourse sometimes has been overtaken by partisan, and often uninformed, opinion.

future developments

Much remains to be done to improve the accuracy and sophistication of existing models, as well as to expand the range of data observations. The urgency with which this work should be completed has increased as the impact of global climate change intensifies. There is an urgent need for properly reviewed research to inform policy decisions in governments around the world to a much greater extent than occurs at the moment. Although many governments have committed themselves to international undertakings such as the Kyoto Protocol, their actual performance nearly always features as the lower end of target brackets and, at the same time, it has become increasingly clear that the existing targets are insufficient to deal with already forecasted changes in the atmosphere. There is a clear need for improved public education concerning the scientific method and ways of separating fact from obfuscation.

In technical terms, in addition to the continuous improvement of the treatment of variables and their integration into existing models, there is an important need to extend the time scales over which predictions of future weather phenomena take place. This will improve understanding of future changes. Second, there is also a need to improve understanding of the interaction among the different components of climate models and current understanding of past events.

Evidence from past ice ages, for example, provides a sound basis for understanding those conditions. However, there have been disparities between observed and predicted conditions, in the case of other factors such as sea temperatures. Even apparently small differences in conditions can significantly affect final results of these models.

sEE ALso: Atmospheric Component of Models; Climate Models; Manabe, Syukuro; Modeling of Ice Ages; Modeling of Ocean Circulation; Modeling of Paleoclimates.

BIBLIogRAPHY. Edward N. Lorenz, The Global Circulation of the Atmosphere (Princeton University Press, 2007); Syukuro Manabe, "Climate and the Ocean Circulation," Monthly Weather Review (v.97/11, 1969); Geoffrey K. Val-lis, Atmospheric and Oceanic Fluid Dynamics: Fundamentals and Large-Scale Circulation (Cambridge University Press, 2006); Spencer Weart, "General Circulations Models of Climate" (cited August, 2007).

John Walsh Shinawatra University

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