Global tropical cyclones and European windstorms in recent decline

• Main Authors: SAUNDERS, MA, LEA, AS
• Format: Article in Journal/Newspaper
• Language: English
• Subjects: Pacific; North Atlantic
• Online Access: https://discovery.ucl.ac.uk/id/eprint/1361615/1/Saunders%2526Lea_submitted2013.pdf; https://discovery.ucl.ac.uk/id/eprint/1361615/

Tropical cyclones worldwide and European windstorms (extratropical cyclones) are the main cause of great weather disasters worldwide but low confidence exists in the quantification and attribution of trends in these storms. This uncertainty is caused by limitations in the quality and quantity of historical data, by the presence of large year-to-year variability in storm counts and by an incomplete understanding of the mechanisms that cause trends. Here we reduce this uncertainty by clarifying the nature, significance and underlying causes of storm trends for the recent 1971 to 2010 period of generally sound surface windspeed data. We find that global tropical cyclones and European winter extratropical storms are mostly decreasing in annual frequency and accumulated power; for the periods 1981 to 2010 and 1991 to 2010 all trends are decreasing and in several cases significantly so. We attribute the recent significant decrease in global tropical cyclone activity to a trend towards colder ENSO (El Niño Southern Oscillation) conditions that produces anomalous zonal flows which tend to inhibit storm spin-up in the North Pacific. We attribute the recent significant decrease in UK and European winter windstorm activity to a decrease in North Atlantic tropospheric thermal wind associated with warmer winter air temperatures at polar and subpolar latitudes. Despite global temperatures rising by about 0.5°C since 1971 our results suggest that climate change has had no discernible positive impact on either globally averaged tropical cyclone activity or on European extratropical cyclone activity; indeed global warming may be contributing to the recent decrease in European extratropical storm activity.