Atlantic precursors for European heat waves?

A new link between the development of heat waves over Central and Western Europe and temperatures in the North Atlantic has been discovered by scientists from the National Oceanography Centre and the University of Southampton.

This finding may be an important factor for the prediction of summer heat waves over Europe, since it suggests the Atlantic Ocean could have a role as a precursor.

The NOC authors of this paper, Drs Aurélie Duchez and Joël Hirschi said “Our study suggests the forecast of European heat waves can potentially be improved by looking out for early warning signs in the ocean.”

The North Atlantic and Europe experienced two contrasting weather events during the summer of 2015: while record cold surface ocean temperature anomalies were observed in the North-East Atlantic, large parts of Central and Western Europe were affected by an extreme heat wave.

This study, published in Environmental Research Letters, finds that these anomalously cold Atlantic conditions preceded the European summer heat wave. Extreme heat loss from the ocean to the atmosphere during the winters 2013-14 and 2014-15 led to the North-East Atlantic cooling by one to two degrees Celsius below the normal spring temperature. Importantly, this cold anomaly extended to seven hundred metres below the surface of the ocean.

The results of this research show that the cold anomaly coincided with the development of a warm ocean temperature anomaly further south, in the Atlantic off the Iberian Peninsula and Morocco. By early June 2015 both the warm and cold anomalies over the North Atlantic became most pronounced. In the second half of June the atmosphere adopted a circulation pattern that led to the development of the European heat wave. In particular, the Jet Stream shifted southwards over the North Atlantic, closely following the warm and cold anomalies that had previously developed.

This link is not unique to 2015, indeed, all major heat waves that have affected Central and western Europe since 1980 were preceded by anomalously cold May temperatures in the North-East Atlantic. This suggests that there may be an oceanic precursor to Central and Western European heat waves.

This research forms part of the National Oceanography Centre’s on-going work into better understanding the link between the ocean and the climate, and was funded by the AXA research fund, the NERC funded projects ODYSEA and DYNAMOC and the Newton fund CSSP China project DYVA and a Leverhulme Research Fellowship.