This post refers to my analysis of recorded annual mean temperature trends at 12 stations located in large cities in the USA. The stations were all with long records (mostly over 100 years) and located in large cities (mostly with populations over a million). The analysis used raw data (as recorded, without any adjustments) as published by KNMI (the Dutch Meteorological Institute). Polynomial curves of best fit were added to the plots.
Normally data from stations located in cities are not suitable for general studies of climate trends (except within urban areas!), because of the uncertain effects of urbanisation on the temperatures. However, city data are often longer than rural data, and it is interesting to compare their long-term trends. It is generally considered that urban temperatures have risen considerably during the past half-century due to increased development (roads, buildings, airports, etc) and increased air pollution (due to industrialisation and vehicles). The urbanisation effect may vary considerably in different cities; for example, if a station is located near a coast there may be minimal urbanisation effect. Another uncertainty with urban stations is that their locations may have changed over the years. Also, prior to the introduction of Stevenson screens in the late 19th century, the instrumentation was different and this will also affect the apparent long-term temperature trends.
This selection of 12 US cities is part of a larger analysis involving 50 cities, worldwide.
Plots are shown below for the twelve US stations. It should be noted that the polynomial fit line (in red) can sometimes be misleading at either end of the series as the line is very dependent on the temperature values in individual years (this sensitivity does not occur away from the start and end of the series).
[ The Portland temperature trend is cyclical with a High in about 1940 and Lows in about 1900 and 2000. The Portland temperature has been essentially constant for the past 60 years. The major increase in temperature was about 1.3 degC between 1890 and 1950.]
San Diego 1850-2015
[ The San Diego temperature has been essentially constant for the past 60 years. The major increase in temperature was about 1.1 degC between 1910 and 1960. ]
[ The Phoenix temperature increased gradually by about 2.5 degC between 1880 and 1980, when there was a sudden increase of about 1.0 degC. The temperature has been essentially constant since 1980. ]
Salt Lake City 1875-2015
[ The Salt Lake City temperature trend has a cyclical pattern with Highs around 1930 and 2010(?) and Lows around 1890 and 1970. The present-day temperatures are about the same as in the 1930s. ]
St Louis 1836-2015
[ The St Louis temperature trend has a cyclical pattern with Highs around 1930 and 2010(?) and Lows around 1870(?) and 1970. The present-day temperatures are about the same as in the 1930s.]
[ The Detroit temperature trend has a cyclical pattern with Highs around 1930 and 2010 and Lows around 1890 and 1970. The present-day temperatures are about 0.5 degC higher than in the 1930s and 1940s.]
[ The Pittsburgh temperature trend has a cyclical pattern with Highs around 1885, 1945 and 2010(?) with Lows around 1910 and 1980. The present-day temperatures are about 1.0 degC lower than in the 1940s. ]
New York 1876-2014
[ The New York temperature trend has been increasing essentially constantly, at a rate of about 1.5 degC/century, over the past 140 years. There is no evidence of any abnormal increase in trend over the past 50 years. The station is located in Central Park so probably is less affected by terrestrial changes (buildings, roads, etc) over the period. ]
[ The Boston data prior to 1871 was incomplete but indicates a cyclical High in about 1780 and a Low in about 1840. The Boston temperature trend has been increasing since 1871. However, the rate of temperature increase reduced significantly (2.2 to 0.9 degC/century) in about 1930. There is no evidence of any abnormal increase in trend over the past 50 years. ]
New Orleans 1893-2014
[ The New Orleans temperature trend is cyclical with Highs in about 1940 and 2010(?) and a Low in about 1970. The present-day temperatures are about 0.5 degC higher than in around 1940. ]
[ The Tampa temperature trend is cyclical with Highs in about 1940 and 2010(?) and Lows in about 1870 and 1970. The present-day temperatures are about 0.5 degC higher than in around 1940. ]
[ The Miami temperatures were essentially constant prior to 1970. However, since 1970 they have been increasing at an average rate of about 2.5 degC/century. ]
Please let me know what you think of my analyses. firstname.lastname@example.org
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.