Detecting ENSO Period Changes in a Proxy Record Spanning the Last Millennium

Open Access
Dorin, Joshua N
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
Committee Members:
  • Klaus Keller, Thesis Advisor
  • anthropogenic climate change
  • ENSO
  • El Nino - Southern Oscillation
  • climate change detection
Anthropogenic activities have increased radiative climate forcings, causing widespread changes to the climate system. The future response of the climate to anthropogenic forcing depends on the responses of the various components of the climate system. One such component is the El Niño-Southern Oscillation (ENSO). The recent occurrence of several ENSO events with increased period raises the question whether anthropogenic climate forcing has changed ENSO. Detecting anthropogenic ENSO period changes requires an estimate of the natural variability (defined here as the unforced variability). Most ENSO change detection studies use instrumental records that have limited ability to capture the full natural variability. Here we analyze ENSO period changes in a published fossil coral record spanning the last millennium. We find a decrease in ENSO period from the pre-1850 to post-1850 intervals, which is significantly (p < 0.1) outside the range of natural variability as approximated by a control run of a global climate model. This result is consistent with anthropogenic ENSO modulation, however, natural forcings need to be considered for a formal attribution test.