Climate variability refers to variability observed in the climate record in periods when the state of the climate system is not showing changes. If the climate state changes, usually characterized by a shift in means, then the frequency of formerly rare events on the side to which the mean has shifted might occur more frequently with increasing climate variability (Salinger, Stigter, and Dasc, 2000).
Climate change is a movement in the climate system because of internal changes within the climate system or in the interaction of its components, or because of changes in external forcing either by natural factors or anthropogenic activities (International Panel on Climate Change [IPCC], 1996).
Natural variability is a characteristic of the global climate and occurs on both long and short time scales. Many climatologists believe that both long-and short-term climatic fluctuations are not random phenomena but organized events which are controlled by forces or energy resources either associated with the earth itself or with the planetary bodies of our solar system. Superimposed on these natural variations are changes induced by human activities. The release of greenhouse gases in the atmosphere in recent years is thought to be the cause of changing climatic patterns. Increases in global surface temperatures and significant interannual climate variability were observed in many regions of the globe during the later half of the twentieth century. The WMO (1998) has reported on warming trends, with proof of climate change and its continuation observed from many parts of the world.
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