Any shift in average climate will almost inevitably result in a change in the frequency of extreme events. In general, more heat waves and fewer frosts could be expected as the average temperature rises, whilst the return period of severe flooding will be reduced substantially if precipitation increases. A 1 in a 100 year event for example, may become a 1 in 10 year event, whilst 1 in a 10 year event may become a 1 in 3 year event. For less adaptable societies in the developing world a shorter return period of extreme weather events may not allow them to fully recover from the effects of one event before the next event strikes. Every region of the world experiences record-breaking climate extremes from time to time.
Droughts are another devastating type of climate extreme.
Frequent reports of record-breaking events suggest that climate extremes are becoming more common. There is no scientific evidence however, that this is the case at the global level. Through the 20 th century there does not appear to be any discernible trend in extreme weather events. In addition, given the large natural variability in climate and the general rarity of climatic extremes it is hard to determine whether they are now occurring as a result of global warming. A more likely explanation is that increased human vulnerability to climate extremes, particularly in developing countries, is transforming extreme events into climatic disasters.