Montoya & Levermann: Small variations in surface winds could have been cause of abrupt climate change during the Last Glacial Maximum

Changes in winds could have been cause of abrupt glacial climate change

ScienceDaily (July 21, 2008) — Spanish and German researchers have carried out a collaborative study that shows how during the last glacial period, small variations in the surface winds could have induced significant changes in the oceanic currents of the North Atlantic, and could even have played a role in the abrupt climate change that occurred at the time.

Scientists from the Complutense University of Madrid (UCM) and the Potsdam Institute for Climate Impact Research in Germany have carried out a study which identifies small alterations in the superficial sea winds as the factors with a key role in the abrupt climatic change that occurred over the last glacial period whose origin is not yet fully understood.

This study, carried out by researchers Marisa Montoya and Anders Levermann, concluded that there is a precise point from which a small variation in the speed of sea winds corresponds to a dramatic change in the Atlantic circulation intensity. According to Marisa Montoya, “If the glacial climate had been in the vicinity of that point, small wind changes could have caused sudden and significant climatic changes during that period.”

The study was based on climatic simulations called Last Glacial Maximum (LGM) (the period of maximum extension of the perpetual ice sheets that took place over 21,000 years ago). These simulations have demonstrated the existence of a threshold after which a small change in wind speed causes disproportionately large changes in the sea current speed. The results indicate that these changes in wind speed could have had a particularly important role in the abrupt climatic change of the last ice age.

Climate simulation of the Last Glacial Maximum is one of the principal challenges for experts in this area. The comparison of results from these simulations with climatic reconstructions based on data gathered from natural elements, such as sea sediments or the oldest ice samples; permit the evaluation of the climatic models in conditions independent from the ones used for their design. The results confirm the relevance of the small variations and help further substantiate the hypothesis about the physical mechanisms responsible for the climatic changes observed in the reconstructions.

Both, the climatic simulations as well as the reconstructions, indicate that variations in the Atlantic Ocean circulation could have been the key mechanism responsible for the abrupt climatic change that took place over the ice age. This circulation plays a fundamental role in the regulation of climate on a global scale, since it transports large quantities of relatively warm water from low latitudes to northern regions, softening the climate of countries like Norway or Ireland in comparison with other regions in the same latitude, but with much harsher climates, like Alaska or New York. This study therefore suggests that the changes in oceanic circulation could have been caused by changes in the speed of surface winds.

M. Montoya & A. Levermann. 2008. Surface wind-stress threshold for glacial Atlantic overturning. Geophysical Research Letters, 35(3) L03608; DOI: 10.1029/2007GL032560