Historical chronology of ENSO and the Nile flood record

Abstract

At present the El Niño system is one of the primary causes of inter-annual climatic variability, not only in tropical regions but also on a global level (Ropelewsky and Halpert 1987; Philander 1989; Kiladis and Diaz 1989; Glynn 1990). A considerable effort is dedicated to the understanding of the El Niño-Southern Oscillation (ENSO) system and its interactions with other kinds of climatic variations, at the decadal/interdecadal (e.g., the Pacific Decadal Oscillation) and centennial (Little Ice Age, MedievalWarm Period) scales (Anderson et al. 1992; Bradley and Jones 1992; Allan et al. 1997; Diaz and Markgraf 2000). Under societal and political pressure, several international research programs aim to decipher the relationships that link ENSO and the present global warming of the planet (Ropelewesky 1992; Cane et al. 1997;Timmermann et al. 1999). These scientific challenges and questions require that long series of climate variations, much longer than those available from instrumental data alone, be compiled and studied. A renewed interest for the climate evolution, at local, regional and global scales, during the last few centuries, is thus justified by the need to understand better the climatic particularities of the Little Ice Age (LIA) and the transition period to the modern situation (19th and 20th centuries) (e.g., Grove (1988), Bradley and Jones (1992, 1993), Allan and d’Arrigo (1999), Allan (2000), Verschuren (this volume), Scott and Lee-Thorp (this volume)). These studies should help to determine how much of the recent global warming results from anthropogenic activities as against a natural post-LIA evolution. Deciphering the relationships between the global state of the planet and the El Niño system (frequency and intensity of individual events, teleconnection links) requires us to document as precisely as possible former climate variations and ENSO manifestations, during warm and cold periods, such as the MedievalWarm Period and the LIA respectively, and to compare them to the present (instrumentally controlled) climate variability (Bradley and Jones 1992; 1993; Diaz and Pulwarty 1994; Jones et al. 2001).