The story of El Nio begins on the eastern margins of the Pacific Ocean. For centuries, Peruvian fishermen have known that the usually cold and nutrient rich waters from time to time become exceptionally warm, accompanied by collapsing fish stocks. At the same time, torrential rain and flooding of the rivers of the Andes occur. This abnormal situation returns every 3-7 years and, since the event usually peaks around Christmas, the fishermen named the phenomenon "El Nio" ("el nio" is Spanish for boy child). For a long time, El Nio was considered to be a weather phenomenon local to the countries of the western part of South America. Only early in the 20th century did scientists begin to realize that a relation exists between El Nio and monsoon conditions in Southeast Asia. El Nio is a result of interaction between the surface of the ocean and the atmosphere in the tropical Pacific. Changes in the ocean impact the atmosphere and climate patterns around the globe, which in turn, impact the ocean temperatures and currents. El Nino spread its effect around the world. It created a refugee crisis in northeast Kenya as tens of thousands of Somali, Ugandan, Ethiopian and Sudanese abandoned flooded camps. By November, the United Nations expected five million people in southern Africa would face famine in 1997/98. Parts of South America, particularly Ecuador, were hit by freak floods in November. Southern Californians were warned to prepare for one of the worst winters in recent history. El Nino drought is even blamed for helping to increase the cost of a cup of coffee, after affecting 1997/98 crops in Africa, Indonesia, Papua New Guinea and parts of South America. But was this year of disaster simply a preview of more terrible El Nino's to come? Are we likely to see more El Nios because of global warming? Will they be more intense? These are the main research questions facing the science community today. Research will help separate the natural climate variation/changes from any trends due to mankind's activities. We cannot fully figure out global warming if we cannot sort out what the natural variability of our planet's weather is. We also need to look at the link between changes in natural variability and global warming.
As mentioned above, as well as in the question, there are accounts of El Nio dating back several hundred years. El Nio is a phenomenon that is caused by natural variations in ocean and atmosphere, and not by man-made changes. Occurrences of El Nino are nevertheless of interest for the research on man-made climate change because the air-sea exchange of carbon dioxide is partially determined by the ocean temperature. Observed concentrations of the atmospheric CO2 content can thus undergo incidental changes in connection with protracted El Nio episodes. All the same, one often reads that the frequency of El Nio events has increased during the last decade, and that this is due to a global heating of the atmosphere. In a speech on emergency management in October 1997, Vice President Al Gore declared (but who listens to him? =) that we are "experiencing an increase in both the frequency and intensity of El Nio events, and that this change may be caused by an increased supply of green house gases to the atmosphere." It is important to realize that no such link has been established for the present day climate.
Frightening scenarios associated with global climate change are popular in the media. The threat of global climate change (due to mankind) is a serious problem that our global society confronts today, but one must also be aware of the fact that there is a large natural variability in weather and climate. In general one should be cautious in assuming/presuming connections between this type of event and global climate change. The connection could also go the other way, although this is not often considered. The forest fires due to El Nio occurring these past few months in the Amazon and Indonesia are contributing strongly to the increase of C02 in the atmosphere, and also reducing the forest cover that absorbs C02. Therefore El Nio appears to be part of the problem of greenhouse warming.
During the fall of 1997 the El Nio phenomenon, and all of the destruction it caused, received a great deal of media coverage. In particular, a lot of attention was directed towards the Indonesian forest fires and their veil of smoke covering large areas in Southeast Asia. Other incidents was also linked to El Nio: high typhoon activity, beach erosion and rising prices of coffee are just a few examples. Due to all this publicity, "El Nio" became the new term in our vocabulary, and interest was reborn in our climate as a whole.
As our reliance on the environment and its climate increases, so does our need to understand it - our need to recognize and predict the weather. El Nino my be increasing in its severity, and it may not. Some say that the string of warm events during the 1990s are evidence that a general warming trend is starting to change the weather; others say that these variations are within normal limits. The fact is we have only a few events to talk about, which means there is no statistical rigor to any argument for or against this idea. It is simply shooting the breeze. We won't have good statistics about El Nio for another hundred years or so (perhaps even longer if it is truly chaotic).