Research examining ancient corals has provided the most detailed evidence to date of the behaviour of the ENSO (El Nino Southern Oscillation) climate pattern over the past 130,000 years and will help climate modellers better predict likely climatic change as the Earth’s atmosphere warms.

No other research has gone back further in time to examine ENSO’s relationship with global climate change. The research, carried out over more than four years by a team led by a scientist from the University of Edinburgh, was completed at AIMS over the past year. The work has been published in the prestigious journal Science.

Dr Alexander (Sandy) Tudhope from Edinburgh is an expert on recovering and analysing climate records locked in ancient coral, in this case massive Porites corals from fossil reefs in Papua New Guinea. He worked with Dr Janice Lough from AIMS, who provided expertise in analysis of climate variability. Other collaborators, from the Australian National University in Canberra and from overseas institutions, contributed various analytical techniques.

ENSO is the most potent source of year-to-year climate variability. The phenomenon profoundly affects the climate of over half the planet and has been responsible for damaging extremes, from drought to floods, in Australia. Despite a rapid rise in scientific understanding of the physics of ENSO, key aspects of the system have remained poorly understood.

The scientists sought to address the uncertainty surrounding the impact of climate change on ENSO strength and frequency with a view to helping predict how the ENSO phenomenon will respond as the Earth warms over the coming years.

Dr Tudhope cautions that the team’s data do not prove or disprove the theory that ENSO has already become stronger as a consequence of human activity. However the data do indicate that ENSO has been sensitive to global climate change in the more distant past. This observation may ultimately lead to more accurate ENSO predictions by research groups who run sophisticated computer climate models, and Dr Tudhope has begun collaborating with two groups who run such programs. The data produced by this research will help fill the gaps that have limited the precision of climate models in the past.

Coral is an ideal material to study as it forms yearly bands, much like the banding seen in trees. The rate at which coral locks slightly atomically different forms of oxygen (known as isotopes) into its skeleton gives a highly-sensitive measure of sea surface temperature and rainfall, the key indicators of ENSO activity. Examining this coral record has shown that ENSO has indeed operated over the past 130,000 years, even during the very cold glacial times, although its intensity has varied.

The team found that during the twentieth century ENSO was strong compared with previous cool glacial times. Part of the continuing uncertainty is not knowing what the comparison would be with times that are as warm as global climate change forecasts would suggest are on the way.

"We are entering uncharted territory," said Dr Tudhope. The Earth is heading towards temperatures warmer than experienced for millions of years, so there is no way of examining what ENSO has done in the past under these conditions. The closest that we may come could be records from the mid-Holocene, 5,000-6,000 years ago, or the last interglacial era, about 120,000-125,000 years ago, when temperatures were on average about 1 degree Celsius higher than presently. It is predicted that global temperatures will rise on average by between 1 and 3 degrees as the greenhouse effect takes effect.

Dr Lough warns that there is no research to prove that ENSO behaviour is linear – that is, if the system behaves a certain way in the presence of an overall cool global climate it doesn’t mean that it will go in the opposite direction should temperatures rise. Much more research is needed to come to such a conclusion.

Dr Tudhope envisages taking a closer look at those warmer periods of the Holocene and last interglacial as his next likely research direction. In addition, he plans to work closely with climate modellers to see what effect these new data have on computer models and where the knowledge gaps still remain.

Download images - JPEG images of coral core drilling and fossil reefs in PNG. 

FOR FURTHER INFORMATION, PLEASE CONTACT:

Dr Janice Lough (AIMS scientist)
Phone: 07-7453 4248
E-mail: j.lough@aims.gov.au