A tabulated ratio of record highs to record lows: a useful marker for on-going climate warming in the United States

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Tuesday, 19 January 2010: 11:15 AM
B217 (GWCC)
Guy Walton Jr., The Weather Channel, Atlanta, GA; and G. Meehl

Presentation PDF (892.9 kB)

For the casual consumer of climate and weather information served by The Weather Channel™ (TWC) cable network and weather.com web site, the notion of anthropogenic-induced climate change (AGW) is a complex and often confusing subject matter. For example, the long time frame over which climate change acts, the noisiness of day to day weather variations, and the abstract notion of the Earth's equilibrium or average temperature are all crucial parts of the theory of AGW, but they can also tend to confound understanding of the basic science of climate change theory and its repercussions. Therefore at TWC, simple tools or information that succinctly and accurately demonstrate the so-called AGW effect or bring the processes responsible for AGW into clear relief, are in great demand. We've developed one such tool called the Climate Scorecard.

Since January 2000 the author has produced a weekly tabulation of high temperature and low temperature records attained at about 200 first-order stations in the U.S. It was very clear from the outset that the running tally or ratio of high temperature records to low was consistently running about 2:1 - which is counter to what one would expect from a stable or steady climate. More recently, starting in November 2006, the National Climatic Data Center (NCDC) provided on-line daily, weekly, monthly and yearly record high and low temperature statistics for first-order and Cooperative stations with at least 30 years of record keeping (see: http://www.ncdc.noaa.gov/oa/climate/research/records/ for details). The author has now converted his own manual tracking of US records to NCDC's national database dating back to 1980.

The trend of the simple high/low temperature ratio does in fact show a value near 1:1 in the early 1980's that then rises well above 2:1 as it approaches present time. The 2:1 ratio is consistent from month to month during the calendar year, as well, from 1997, which was the warmest year globally on record, to the present time. The rate of increase in this ratio over the period amounts to about 4-5% annually. The week to week noise or variability of the high/low ratio is pronounced, but with time averaging over seasons or years the ever increasing ratio readily emerges from the data. The High/Low ratio statistic is the centerpiece of the Climate Scorecard, and gives on-air Meteorologists and Climatologists a simple and powerful metric for communicating the observed longer term warming. It also provides a concrete linkage between climate and weather, which is often in short supply in the broader discussion on AGW. This presentation will detail how The Weather Channel Climate Scorecard was developed, present the basic records data and how it trends over time, as well as discuss future uses of this robust and useful climate and weather tool.