Climate Variations and Abnormal Weather

Abstract

We have experienced many abnormal weather conditions in recent years in Japan. For example, we had abnormally cool summer in 2003, abnormally hot summer in 2004 and 2007, and heavy snowfall in winter of 2005/6. Disasters caused by those abnormal weather conditions are increasing. Such a situation is not only the case in Japan but rather ubiquitous in the world. People are apt to think that it is due to global warming of the anthropogenic origin. However, it is a too simplistic view ; the abnormal weather conditions are consequences of natural climate variations under the global warming trend. Typical examples of those climate variations are El Niño in the Pacific Ocean and the Indian Ocean Dipole Mode. Because of the progress in prediction science, the climate variations can now be predicted to some extent by use of a state-of-the-art ocean-atmosphere coupled model several seasons prior to their occurrences. To achieve this, we need to have ocean-atmosphere data as initial conditions and a high-performance supercomputer. Because of the warming of world oceans, climate variations are modulated in recent years. El Niño is becoming more frequent and stronger. The Indian Ocean Dipole Mode is also becoming more frequent. Global impacts of such climate variations are either canceling or augmenting each other ; they are different from place to place. We are promoting efficient delivery of prediction results for preventing disasters as well as science for predicting climate variations.