Explaining Extreme Events of 2011 from a Climate Perspective

E very year, the Bulletin of the AMS publishes an annual report on the State of the Climate [e.g., see the Blunden and Arndt (2012) supplement to this issue]. That report does an excellent job of documenting global weather and climate conditions of the previous year and putting them into accurate historical perspective. But it does not address the causes. One of the reasons is that the scientists working at understanding the causes of various extreme events are generally not the same scientists analyzing the magnitude of the events and writing the State of the Climate. Another reason is that explaining the causes of specific extreme events in near-real time is severely stretching the current state of the science. Our report is a way to foster the growth of this science. Other reports, such as those by the Intergovernmental Panel on Climate Change (IPCC), have focused on understanding changes over longer time scales and larger geographic regions. For example, assessing the state of the climate and science, IPCC (Field et al. 2012) concluded that “it is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures at the global scale” and that “there is medium confidence1 that anthropogenic inf luences have EXPLAINING EXTREME EVENTS OF 2011 FROM A CLIMATE PERSPECTIVE