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Warming Trend: A Decade-by-Decade Analysis

Women-Ice-Skating-by-J.R.-Taylor

 

Monthly temperatures for New York (Central Park) go back to 1869.  With this century-and-a-half treasure trove of data in front of me, I calculated each decades' monthly temperatures.  As I immersed myself in the data, a story emerged - New York was noticeably cooler before 1930, and every month's coldest decade occurred in that period.  A second story was that the decade of the 2010s became the warmest decade for eight months (April thru October, and December).  Other findings:

 

  • Comparing pre-1930 decades with 1930 onward shows that March has warmed the most (+3.5 degrees), followed by February (+3.2).  The least warming has occurred in September (+1.4 degrees) and June (+1.5).
  • The biggest difference in temperature between a month's coldest and warmest decade has occurred with February and March.  In the 1880s March's mean temperature was 35.4° degrees while it was 42.9° in the 1980s, a warm up of 7.5 degrees.  In February the pre- and post- temperatures were 29.4° and 36.3°.
  • While March in the years between 1930 and 1999 was 3.5 degrees warmer than the six decades before 1930, in the 21st century it has been 4.5 degrees warmer.  June, July and October were just 0.2 degrees warmer than their respective months in the 1930-1999 period.
  • Until the 2010s the warmest decade for September and October was the 1940s.
  • In the first two decades of the 20th century February was colder than January by a significant margin (29.9° vs 32.3°).
  • Worldwide, the first decade of the 21st century has been the warmest on record, but New York's warmest decade was the 1990s. (However, the 2000s had NYC's mildest Aprils and Novembers.)  

 

COLDEST & WARMEST DECADES BY MONTH
         
  Coldest Warmest
    Mean   Mean
  Decade Temp Decade Temp
January 1880-89 28.7 1990-99 34.8
February 1900-09 29.4 1990-99 36.3
March 1880-89 35.4 1980-89 42.9
April 1870-79 48.1 2010-19 54.2
May 1870-79 60.1 2010-19 64.3
June 1910-19 69.0 2010-19 72.2
July 1880-89 74.6 2010-19 78.8
August 1880-89 72.0 2010-19 76.4
September 1870-79 65.4 2010-19 70.5
October 1890-99 55.5 2010-19 59.2
November 1870-79 42.0 2000-09 48.6
December 1870-79 32.8 2010-19 39.8
Source: NOAA Local Climatological Data

 

TEMPERATURE TRENDS OVER THREE PERIODS
         
  Mean Temperature Degrees Diff
  Before     2000-2019 vs
  1930 1930-1999 2000-2019 Before 1930
January 31.0 32.6 33.0 2.0
February 30.9 33.9 35.6 4.7
March 38.3 41.5 42.7 4.4
April 49.5 52.1 54.0 4.5
May 60.7 62.6 63.2 2.5
June  70.1 71.6 71.8 1.7
July 75.2 76.9 77.4 2.2
August 73.3 75.3 76.1 2.8
September 67.0 68.3 69.7 2.7
October 56.0 57.8 58.2 2.2
November 44.0 47.3 47.7 3.7
December 34.4 36.6 38.8 4.2
FULL YEAR 52.6 54.8 55.7 3.1
         

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