The importance of abrupt climate change, and its inclusion in the development of climate change adaptation strategies, has been increasingly emphasized in the last decade. A sudden change in climate is brought about by complex interactions in the climate system, which can give rise to strong positive feedback mechanisms. Paleoclimatic studies have shown that abrupt climate changes have happened in the geologic past. Further, studies of future climate change indicate the potential for the sudden collapse of the thermohaline circulation under scenarios of global warming, with major implications for the climate of Europe. However, abrupt climatic changes are not just events of the geologic past or a computer-simulated future: they have occurred in recent history and have had serious consequences on society and the enviroment. The prolonged Sahel drought that began in the late 1960s and the Dust Bowl of the 1930s are examples of sudden climate changes of the twentieth century. Apart from these, however, there has been no systematic survey of recent climate history to determine the prevalence of abrupt climate changes. Given the potential cost of these abrupt changes, there is a need to investigate historical records for evidence of other sudden climatic changes in the more recent past in different regions of the world.

Here we analyze the Climate Research Unit global historical rainfall observations (covering the years 1901-2000) using wavelet analysis to detect regions that have undergone large, sudden decreases in rainfall. We show that in the twentieth century, aside from the Sahel, about 30 regions in the world have experienced sudden climatic changes. We also illustrate some of the potential consequences of these abrupt changes and show that these events have had major impacts on social and environmental conditions throughout the world. The identification of certain regions that are susceptible to sudden climate change in the recent past may help develop strategies for dynamical analysis, adaptation and improved resilience-based management of these environmental systems.