It was a hot topic in the news this summer: the current El Niño (2015 – 2016) could be one of the strongest El Niño events ever measured and could break all records. According to the NOAA (2015) the current El Niño is a strong one and will last throughout the 2015-2016 winter. Past experiences do not provide good prospects for this year’s El Niño, if we are to believe the news sites. The El Niño event of 1997 – 1998 caused catastrophic floods in Peru and Ecuador, while inland South America, Indonesia and Australia were faced with severe droughts and wildfires (Cane, 2005), with ~$ 25 billion costs for the U.S. economy alone. But what is El Niño? What happens during an El Niño event and what can science tell us about this phenomenon?
During an El Niño event the oceanic trade winds over the Eastern Pacific weaken, causing warm ocean water in the western Pacific to flow to the east reducing the upwelling of cold water from the deep sea. As a result, SST’s along the South American coast increase, further inducing convergence in the atmosphere (McPhaden et al., 2006; Donders, 2005). The change in SSTs in the central and eastern Pacific causes shifts in precipitation patterns across the Pacific. In Australia, Indonesia and surrounding areas the climate becomes drier, while the west coast of Southern America experiences heavy rainfall. El Niño events occur once every 2 – 7 years around Christmas, but can vary in intensity. The impacts of El Niño events are not only noticeable around the Pacific: through teleconnections El Niño’s can affect the frequency, intensity and spatial distribution of hurricanes, cyclones and storms around the world (McPhaden et al., 2006).
So what about climate change? Will this lead to stronger and more frequent El Niño’s? Unfortunately, there’s not an easy answer to these questions. The behaviour of ENSO in a world with anthropogenic induced climate change is still highly uncertain, topic of intense debate and an intensely studied phenomenon in science. Also, there are still uncertainties about the exact mechanisms and causes of variations in amplitude and frequency of El Niño events and its counterpart La Niña. This is where I and my PhD project come in.
Reconstructing past ENSO dynamics
Although it is very difficult to predict what will happen in the future, we are certain of what happened in the past. So, historical and geological records can tell us a lot about variations in amplitude and frequency of El Niño events that have already occurred. I’m working on ENSO reconstructions for the Holocene (± the past 10,000 years), with a special focus on time intervals with exceptional changes in the ENSO. To do this I’m combining my background in ecology and ecophysiology with earth sciences and physical geography. In the (sub)tropics the link between the ENSO and precipitation patterns is so strong that individual El Niño/La Niña events directly influence plant growth and vegetation compositions. The resulting vegetation dynamics are well reflected in the fossil record by pollen and spores. The Palaeoecology team at Utrecht University (the Netherlands) and prof. dr. Donald T. Rodbell at Union College (USA) and his colleagues have collected several sediment cores from lakes in Ecuador, a key ENSO region. These sediment cores contain a continuous record of fossil pollen for the entire Holocene and by counting and identifying these pollen and spores I can reconstruct vegetation dynamics of the last 10,000 years. I can then use these vegetation records to quantitatively reconstruct past climate conditions which will give us a lot of information about past ENSO dynamics. I’m currently working in the laboratory and spending a lot of time behind a microscope, so I hope to update you soon on my proceedings!
CPC/NCEP/ NOAA, 2015: El Niño / Southern Oscillation (ENSO) Diagnostic Discussion:
Cane, M. A. (2005). The evolution of El Niño, past and future. Earth and Planetary Science Letters,
164, 1 – 10.
McPhaden, M. J., Zebiak, S. E., & Glantz, M. H. (2006). ENSO as an integrating concept in earth
science. Science, 314, 1740 – 1745
Tudhope, A. W., Chilcott, C. P., McCulloch, M. T., Cook, E. R., Chappell, J., Ellam, R. M., Lea, D. W.,
Lough, J. M., and Shimmield G. B. (2001). Variability in the El Niño-Southern Oscillation through
a Glacial-Interglacial cycle. Science, 291, 1511 – 1517.
Donders, T. H. (2005). Reconstruction of El Niño – Southern Oscillation variability during the
Holocene. PhD thesis, LPP Contributions Series No. 20, LPP Foundation.