Warming Trend: A Decade-by-Decade Analysis

 

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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