If Local Weather Was Our Only Indicator

It is understandably difficult for individuals and communities to recognize the effect of gradual climate change when it occurs in the context of local weather patterns, which normally vary from year to year. This recognition difficulty delays discussion of the causes of climate change and forestalls adjustments in policy and action. In this article, the authors estimate the length of time it would take a majority of localities to simultaneously acknowledge climate change if the only source of information about climate change was local weather. They run computer simulations using U.S. weather station data from 1946 to 2005. Local weather is allowed to vary randomly around a constant mean (models assuming no climate change) or a rising mean (models assuming climate change). They run separate models for annual average temperature, annual maximum temperature, and annual variation in monthly precipitation, varying the definition of unusual weather from 0.5 to 2.5 standard deviations from the historic average and varying the number of consecutive years of unusual weather required to reject the belief of normal variation and accept the belief of climate change from 1 year to 5 years. When it is assumed that acknowledgment of climate change requires three consecutive years of weather, a full standard deviation or more above the historic mean, it requires, depending on which weather event is being modeled, an average of 21 years, 86 years, or 82 years for a majority of localities to be in a state of climate change belief.