Detecting Climate Change through Means and Extremes

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Abstract

This study investigates how the climate is changing at individual weather stations around the world by measuring means and extremes. Extensive python code was written to read in the daily data from thousands of stations and compute average yearly temperature, precipitation, and extremes such as heat waves, cold spells, very wet days and dry periods. A best fit line and goodness-of-fit statistic were computed for each statistic at each station. All these linear trends were collected into histograms and geographic distribution plots. The following conclusions were drawn from stations with over 65 years of data, which includes 1243 stations for temperature and 4534 for precipitation. It was found that the earth is undergoing significant changes: 97% of all stations are increasing in temperature since 1950, averaging 4oF per century. All measures of extreme heat are increasing, and all measures of extreme cold are decreasing. Almost all stations are recording significant increases in the number of warm days (days above the station’s reference 90th percentile) and heat waves (three consecutive warm days). The warmest day of the year is getting hotter. Worldwide there are fewer cold nights and cold spells. The number of frost nights (nights below freezing) are significantly decreasing, averaging 25 fewer frost nights per year over a century. Changes in precipitation vary by geography: some regions are drier (western Europe, eastern and western Australia), while others are wetter (eastern U.S., northern Australia). This study confirms that the earth’s climate is rapidly changing in both means and extremes.