Research
El Niño-Southern Oscillation (or ENSO) is the largest source of natural climate variability on the planet. Climatic extremes including drought, flooding, bushfires, dust storms and tropical cyclone activity affecting over 60% of the Earth are modulated by fluctuations in ENSO. Nevertheless, its history is relatively unknown. Meteorological data generally only covers the past 150 years, which is insufficient to assess the significance of late 20th century ENSO extremes.
In 2002, Joelle began an Australian Postgraduate Award funded PhD to reconstruct a 500 year history of ENSO using a range of tree-ring, coral, ice-core and documentary records. The aim was to place recent extremes into a 500 year context on natural (i.e. pre-industrial) climate variability. The multi-disciplinary research she conducted was the first Australian effort to reconstruct a global history of ENSO events.
In 2003-04, she was a visitor at the Tree-ring Laboratory at the University of Auckland updating Kauri tree-ring chronologies from Northland, New Zealand, by sampling live trees. Spanning 3,722 years, the Kauri record is now the longest (continuous) tree-ring in Southern Hemisphere, and the longest El Niño-sensitive tree-ring record in the world.
After working on the Kauri record and its regional climate signal, she looked at a range of other tree-ring, coral, ice-core and historical proxy climate records known to be ENSO-sensitive. This included looking at diverse range of data including Peruvian ice-cores, the Nile River flood record, historical Indian drought, tree-rings from Mexico and corals from Australia’s Great Barrier Reef.
This provided a more “global” picture of past ENSO variability, allowing recent climate variability to be assessed from a long-term, “multi-proxy” perspective. It was the first Southern Hemisphere effort to reconstruct ENSO records using widespread climatic data.
Currently, the reconstruction is the most comprehensive year-by-year record of global ENSO events. Significantly, it introduces the first extensive La Niña event chronology compiled to date. Annual record of historical ENSO events can provide an independent means of verifying climate model simulations and are of use to archaeologists and social scientists interested in human responses to climatic events.
See the Publications page for more details.