The North Atlantic warming and cooling cycles are known as the Atlantic Multi-Decadal Oscillation (AMO) and new research from the University of Reading suggests that the warming cycle that has been in place since the 1990s may be the cause of the wetter summers the UK and northern Europe have been encountering lately.
Published in the journal Nature Geoscience the research found that North Atlantic warming throughout the 1990s coincided with a shift to wetter summers in the UK and northern Europe and drier, hotter summers around the Mediterranean.
The patterns the researchers found match those experienced this past summer during which the UK had its wettest summer in a hundred years, while the Mediterranean countries suffered temperatures of 40 degrees centigrade and higher.
The AMO swings every few decades from warmer to cooler. The current warm phase is similar in pattern to conditions that persisted throughout the 1930s, 40s and 50s prior to three decades worth of cooler conditions.
Computer simulations suggest that these changes in ocean temperatures affect the atmosphere directly above the ocean, meaning that warmth in the North Atlantic results in a trough of low pressure over western Europe in summer and directs rain-bearing weather systems directly into the UK.
The previous North Atlantic warm phase also saw a run of wet summers over the UK with notable events including the August 1952 Lynmouth floods and severe flooding during August 1948 which closed the east coast mainline railway for three months.
Professor Rowan Sutton, Director of Climate Research in the National Centre for Atmospheric Science and a researcher in the University of Reading’s Walker Institute, led the research.
“The North Atlantic ocean has alternated slowly between warmer and cooler conditions over the last 100 years,” Sutton said. “We saw a rapid switch to a warmer North Atlantic in the 1990s and we think this is increasing the chances of wet summers over the UK and hot, dry summers around the Mediterranean – a situation that is likely to persist for as long as the North Atlantic remains in a warm phase.
“A transition back to a cooler North Atlantic, favouring drier summers in the UK and northern Europe, is likely and could occur rapidly. Exactly when this will happen is difficult to predict, but we’re working on it.”
Source: The University of Reading