Highly variable El Niño-Southern Oscillation throughout the Holocene

Area of Science:

• Paleoclimatology
• Climate dynamics
• Oceanography

Background:

• The El Niño-Southern Oscillation (ENSO) significantly impacts global climate patterns annually.
• The ENSO's sensitivity to anthropogenic greenhouse gas emissions remains uncertain.
• Understanding ENSO's response to forcings is crucial for climate change projections.

Purpose of the Study:

• To analyze long-term ENSO variability using fossil coral records.
• To assess ENSO's response to past natural forcings and compare it with model predictions.
• To investigate the potential detectability of anthropogenic impacts on ENSO.

Main Methods:

• Utilized fossil coral reconstructions of ENSO activity spanning the last 7000 years.
• Focused analysis on data from the Northern Line Islands, a key ENSO region.
• Compared paleoclimatic ENSO variance with instrumental records and climate model outputs.

Main Results:

• Fossil corals reveal highly variable ENSO activity over the past 7000 years.
• No systematic trend in ENSO variance was found, contradicting some insolation-driven models.
• Twentieth-century ENSO variance, while high, is not unprecedented in the paleoclimatic record.

Conclusions:

• Long-term ENSO variability is substantial, potentially masking forced climate change signals.
• Detecting anthropogenic influences on ENSO may be challenging against a backdrop of high internal variability.
• Past ENSO behavior suggests resilience and complex responses to external forcings.