Twentieth Century Global Cooling

The media for the past few decades has been dominated by concern about “global warming”. This concern is part of a larger concern about “climate change”, concentrated on perceived increases in surface air temperatures, sea temperatures, sea level rise and extreme weather events.

This blog is concerned only with surface air temperatures, specifically on the recorded decrease (ie cooling) that occurred in many parts of the world during the mid-twentieth century

In April 1975 Newsweek magazine printed a full-page article on global warming.  See scan of whole page at the end of this blog.

 

An analysis of 50 long-term temperature records from stations located world-wide in rural areas or in small towns identified 33 stations with significant cooling during the mid 20th century. Another 13 stations had plateau trends (ie approximately level trends) during the mid-20th century.     World 50 Temperatures

The analysis used raw data (as recorded, without any adjustments) as published by KNMI (the Dutch Meteorological Institute) or BOM (the Australian Bureau of Meteorology). Polynomial curves of best fit were added to the plots.

A typical plot of annual mean temperatures (at Morris, Minnesota, USA) illustrates the reason for the cooling concern.  At Morris (a small rural town) the annual mean temperature trend dropped by 1.0 degC between 1929 and 1973.

The 33 stations with well-defined cooling (exceeding 0.1 degC) are shown on the following map and are listed in the table below.

Map of Stations with Significant 20th Century Cooling

Summary of 20th Century Cooling Analysis

The cooling periods occurred mainly during the period 1930-1970, although cooling also occurred at earlier or later dates at some locations.  The average duration of the cooling period was 36 years and the average amount of the cooling trend was -0.7 degC.

 

In the sample of 50 stations investigated 66% (33/50) of the stations had extended periods of cooling trend exceeding -0.1 degC.  The average amount of the cooling trends was -0.7 degC, within a range of -1.7 degC to -0,2 degC.

An additional 26% of the stations had essentially flat (plateau) temperature trends for extended periods during the mid-20th century.

Links to the annual temperature analyses at the 33 stations are at:

(for Nome, Prince Albert, Eureka, Natashquan, Aberdeen, Morris, Kosciusko, Faaa, Belize, Punta Arenas & Orcadas)

(for Akureyri, Thorshavn, Valentia, Luqa & Funchal)

(for Salehard, Turuhansk, Viljujsk, Ohotsk, Jiuquan, Tengchong, Urakawa, Sandakan, Port Blair & Minicoy)

(for Pietersburg, Marble Bar, Darwin, Richmond, Moruya Heads, Hokitika & Amundsen-Scott).

 

The April 1975 Newsweek Article

 

Please let me know what you think of my analyses.    brigun@westnet.com.au

 

The Author:                                                                                                                                    

This article was written by Brian Gunter of Narooma, NSW, Australia. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.

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