In Search of Paleo-ENSO

摘要

In the past several years there has been a shift in the perceived importance of the tropical Pacific Ocean to global climate on glacial-interglacial and millennial time scales. Modeling studies have indicated that the El Nino-Southern Oscillation phenomenon (ENSO), which is the primary source of year-to-year variations in tropical sea surface temperature (SST) in the modern world, may be highly sensitive to orbital influences. In these studies, the dynamical interaction between the atmosphere and ocean in the tropics is influenced by the modulation of the seasonal cycle of solar radiation by the precession of Earth; simulated tropical Pacific SST anomalies, akin either to warm El Nino or cold La Nina events, can be sustained for several hundreds to thousands of years and generate a globally synchronous climate response. Just as ENSO-related SST variations exert a major effect on modern atmospheric circulation and climate, models suggest that changes in tropical Pacific SST patterns might also have had large consequences for global climate during the last glacial maximum (LGM) about 20,000 years ago. There is, however, still a large uncertainty as to the relationships between ENSO characteristics and the background mean climate state. Given that instrumental data are limited to the past century, paleoceanographic records can provide better constraints for assessing future effects of global warming on ENSO and their ramifications for Earth's climate.