The prevailing theory and fear that rising global temperatures could result in permanent El Niño conditions have been called into question by an international research team on the basis of growth rings of prehistoric clams. A transition to a permanent El Niño state could have a major impact on socioeconomic and ecological systems worldwide.

Higher temperatures

The El Niño Southern Oscillation (ENSO) is characterised by unusually warm ocean temperatures in the eastern Equatorial Pacific occurring once every 2 to 7 years and lasting 9 months to 2 years. It can wreak havoc on global weather ranging from droughts in one place to torrential rainfall in another.

Earlier this year scientists already discovered that the El Niño Southern Oscillation continued throughout the Pliocene, when temperatures were 2 to 3 degrees higher than present day. The new study published online in Geophysical Research Letters proves the same for the Eocene epoch, when Earth temperatures rose by 5 to 7 degrees and deep sea temperatures by about 4 degrees.

Growth rings

Like trees, clam shells show growth rings, wider rings for periods when circumstances were good and narrower ones that were grown in worse times. The fossilised clams that were studied were of a species that can live to be over a hundred years old. Their shells showed the scientists a two to seven year periodicity, which corresponds directly with El Niño periodicity. Fossilised driftwood found in the same sediment layer (thus of the same age) showed similar patterns.

Nothing to worry about?

These results led the team to conclude that despite the high temperatures during the Eocene the ENSO system was still active. Let’s hope ENSO will still be so kind as the planet warms. It would mean we will not have to worry about a disturbance of global hydrological cycles, on top of all the other problems associated with rising temperatures.

© Jorn van Dooren | www.bitsofscience.org