Shifts in Pacific warming could increase cyclone activity

New research indicates that there has been a geographical shift in warming in the Pacific Ocean in the last 50 years which could cause changes in cyclones and weather events. Tropical cyclones involve large and rapid circulations of air, which are often accompanied by destructive weather, especially hurricanes, and have devastating effects. The IPCC Fourth Assessment Report on climate change projects an increase of extreme weather events. Information on the trends and predictability of harsh weather events can be useful when taking measures with regard to disaster prevention and preparedness as well as intervention in the event of disaster. Researchers studied occasions over the last 50 years when the sea-surface temperature (SST) varied significantly from its normal range. They identified three types of temperature changes: Central Pacific Warming (CPW), Eastern Pacific Warming (EPW) and Eastern Pacific Cooling (EPC). EPW is identical to that of the conventional El Ni�o. From 1950 to 2006, there have been nine years where EPW events dominated, five CPW years and 12 EPC years. CPW events appear to have increased at the expense of EPW events, especially since the early 1990s. The study analysed the anomalies in SST to locate where these events have tended to occur. For CPW events, these are located near the dateline (180� longitude) and for EPW events they are located 60� to 80� east of this. CPW temperature variations are generally smaller and associated with different outcomes. For example, a CPW event produces reduced rainfall in the western US and increased rainfall in the eastern US, which is opposite to what is expected in an EPW event. The greatest number of cyclones occur between August to October. Overall, there are more cyclones in CPW events than in EPW events. For example, 2004 was a CPW year where 15 tropical cyclones developed in the North Atlantic, an unusually high figure.