Climate Fact: Record Highs to Record Lows Ratio

In Brief: From January 2000 to October 24, 2010, 310,531 record high temperatures were set across the contiguous United States. During the same period, 152,087 record low temperatures were set, giving a record highs to record lows ratio of more than 2:1.

There are close to 5,000 quality-controlled weather stations across the United States and everyday at least some of these locations will set record high or record low temperatures. During periods of warming – even periods of pronounced warming – daily record low temperatures will continue to be set. Daily record high temperatures are also set during periods of cooling. Yet, it is not the existence of record highs or record lows that indicate whether a warming or cooling trend is occurring. Instead, it is the proportion or ratio of record highs to record lows that indicates whether the climate is getting warmer or cooler. During the warmest decade on record, the 2000s, lots of daily record lows were set. Between January 1, 2000 and October 24, 2010, 152,087 record lows were set. All other things being equal – meaning that there is no increase or decrease in average surface temperature – the ratio of record highs to record lows should be around 1:1. But, from January 2000 to October 24, 2010, 310,531 record high temperatures were set, giving a high to low ratio of more than 2:1. The disparity between record highs and record lows reflects the above normal temperatures experienced over the last decade.

Source: Meehl, GA et al. “Relative increase of record high maximum temperatures compared to record low minimum temperatures in the U.S.” Geophysical Research Letters 36 (2009): L23701.

United States Record Daily Highs vs. Record Daily Lows

The chart (left) has been provided courtesy of The Weather Channel and is based on data provided by NOAA’s National Climatic Data Center. The chart is available for further distribution and use on-air provided the embedded “The Weather Channel” and “NOAA: NOAA/NESDIS/NCDC” logos remain in the image.

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