Solar Forcing of ENSO on Century Timescales

• Published in: Geophysical research letters 2023-10, Vol.50 (20), p.n/a
• Main Authors: Wilcox, Paul S., Mudelsee, Manfred, Spötl, Christoph, Edwards, R. Lawrence
• Format: Article
• Language: English
• Subjects: Aleutian low; anthropocene; Anthropogenic factors; Atmospheric circulation; Atmospheric conditions; Caves; Climate; Climate change; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; ENSO; Future climates; Global warming; Human influences; Irradiance; Natural variability; North Pacific; Regional climates; Solar irradiance; Southern Oscillation; speleothems; Variability; Volcanic eruptions
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL105201

Understanding how El Niño‐Southern Oscillation (ENSO) responds to natural variability is of key importance for future climate projections under a warming climate. However, there is no clear consensus on what drives ENSO's variability on centennial timescales. Here, we find that the epikarst in southeastern Alaska is effective at filtering ENSO and solar irradiance signals from the Aleutian Low regional climate, which are subsequently recorded in speleothem proxy data. By applying a correlation test, we find that ENSO was significantly influenced by solar irradiance over the past ∼3,500 years. This relationship dissolved after ∼1970 CE, with ENSO now being dominated by anthropogenic forcing. This implies a new ENSO mean state that will need to be incorporated into future climate projections. Plain Language Summary Although El Niño‐Southern Oscillation (ENSO) is one of the most important climate phenomena globally, it is currently unknown how ENSO responds to natural variability on timescales over 100 years. Natural variability refers to periodic changes in climate due to either solar forcing, the circulation of the atmosphere and ocean, volcanic eruptions, and other factors, irrespective of human intervention. Here, we help solve this problem by studying deposits in caves (speleothems) from Alaska. The speleothems are excellent at capturing atmospheric conditions over the past 3,500 years, and show that solar forcing was significantly controlling ENSO variability. However, the speleothems also show that humans have altered this natural variability, with ENSO entering a new mean state after ∼1970 CE. Key Points Speleothems from southeastern Alaska capture El Niño‐Southern Oscillation (ENSO) variability through a teleconnection with the Aleutian Low ENSO variability was strongly influenced by solar forcing before ∼1970 CE ENSO significantly changed properties at ∼1970 CE, likely due to anthropogenic forcing