Record Highs vs. Record Lows – A Climate Change Duel?

It seems like breaking a record high temperature happens all the time nowadays. Breaking record lows, it seems, is much more rare. With several record lows last week I went back and decided to take a look at the climatology of record highs and lows over the last 60 years. Using Sikorsky Airport in Bridgeport I tallied the number of record highs and record lows per decade (I excluded days where a record high/low occurred in more than one year for simplicity).

1950s

  • 64 Record Highs
  • 64 Record Lows
  • 1:1 ratio of record highs to record lows

1960s

  • 31 Record Highs
  • 88 Record Lows
  • 0.4:1 ratio of record highs to record lows

1970s

  • 49 Record Highs
  • 47 Record Lows
  • 1:1 ratio of record highs to record lows

1980s

  • 33 Record Highs
  • 62 Record Lows
  • 0.5:1 ratio of record highs to record lows

1990s

  • 65 Record Highs
  • 26 Record Lows
  • 2.5:1 ratio of record highs to record lows

2000s

  • 53 Record Highs
  • 15 Record Lows
  • 3.5:1 ratio of record highs to record lows

You can see a few things from the data. One is that the 1960s were very cold with a phenomenal number of record low days and relatively few record high days. This can be found across the country. The 1980s, regionally, were relatively cool as well with almost twice as many record lows than record highs. The 1980s were unusual in a sense because the “cold” was not something seen nationally.

In the last 20 years, however, the number of record lows has dropped off substantially. For every 3 record highs there is about one record low in Connecticut. Here’s how the picture is nationally, courtesy of UCAR. You can see a nationwide cool down in the 1960s and 1970s and a dramatic reduction in number of record low days in the 1990s and 2000s.

What is the cause of the reduction? I believe the answer is two-fold. One reason is increased urbanization has lead to an increased urban heat island effect. This can lead to higher daily maximums and warmer overnight lows.

A second reason is likely global warming from both natural and anthropogenic (human) sources. A 2009 paper by Meehl, et al. says that climate change models show more warming at night which would reduce the number of record lows and a smaller amount of warming during the day. This means the ratio of record highs to record lows would continue to increase even if the number of record highs stayed flat or increased slightly.

The Intergovernmental Panel on Climate Change in 2007 released this finding about the current state of the world’s climate.

It is very likely that over the past 50 years: cold days, cold nights and frosts have become less frequent over most land areas, and hot days and hot nights have become more frequent. It is likely that: heat waves have become more frequent over most land areas.

The bottom line is that record highs are occurring more frequently than record lows in Connecticut and in the United States. With climate change the ratio of record highs to record lows should continue to grow over subsequent decades.

Ryan

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