How much global warming may have affected an individual extreme event-Sandy, the California drought, thousand-year floods in West Virginia or Louisiana-is a separate and much harder question. These long-term trends apply to averages across groups of similar events, usually spread over large areas-a national increase in heavy rain events, for example-not necessarily to a specific event in a particular place. Photo by Ray Garrido, courtesy of Washington Department of Ecology. According to a NOAA analysis, tidal flooding events in nearby Seattle have increased from roughly once every 1-3 years around 1950 to once every 6-12 months today. Nuisance high-tide flooding from Puget Sound in Port Orchard, Washington, on January 6, 2010. Since 2011, NOAA scientists have been serving as lead editors for a special annual report dedicated to studies that attempt to explain the causes of some of the previous year's extreme events.Extreme event attribution is hard to do in "real-time" because it depends on carefully planned experiments using high-resolution climate models, which can require significant computer processing power and time to run.Knowing whether global warming influenced the probability or intensity of an extreme weather event can help people in affected communities develop recovery and resilience plans that match their future risk.Extreme events related to heat and rainfall are easier to study than extremes related to fires, droughts, or tornadoes.Extreme event attribution can tell us whether global warming made an event more likely or more severe, but it can't tell us if global warming "caused" an event in a yes-or-no sort of way.Extreme event attribution is the science of detecting whether manmade global warming was one of them. All extreme events have multiple causes.
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