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No doubt that Earth’s climate is the most important natural resource. It affects all human activities, food production, water resources, habitants, social and economic development, cultural affairs and health. Climate is normally seen as the average state of the atmosphere observed as weather for a longer period of time. It is usually described by the mean state together with measures of variability such as the standard deviation. The climate system is a complex system, it is controlled not only by what happens in the atmosphere, but also in oceans, the cryosphere (glaciers, sea ice, ice caps), geosphere (the earth’s solid surface) and the biosphere (living organisms). Also, it involves the interactions between these spheres and the feed back loops which are still difficult to predict. A great concern is being given now to climate variabilities and the possibilities of human induced climate change. The social and economic consequences that could result from climate change would affect the developing countries far more because of their limited resources. Different perspectives are now observed regarding possible future climate changes. Using global climate models some scientists attribute the possible future climate changes to human release of green house gases and urge the world community to take the necessary measures to avoid such catastrophic changes. Another group considers that the ability of the global climate models to simulate future climate is limited since many important dynamical and physical atmospheric processes, specially the small scale ones, cannot be represented explicitly in models and are included in approximate forms. Accordingly, there are significant uncertainties in the models products. A third group considers that the climatic changes are usually due to natural processes mostly the solar activity. There are substantial scientific evidences showing that the increase in atmospheric carbon dioxide, produce many beneficial effects upon some living organisms in addition to the cooling effect. How reliable are the human induced climate changes? This question has arisen and needs to be answered in a plausible way for the sake of the developing countries which are vulnerable to such phenomenon. Moreover, the climate impacts are expected to be different from place to another, accordingly there is a great need to evaluate the used climate change models generally, technically and to conduct regional and national projections of future climate changes and variabilities to help policy makers and planners on their future decisions and plans.
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