Analyzing Temperature Change using World Class Stations

This article was first posted on July 28, 2014 at Watts Up With That.

This is a study to see what the world’s best stations (a subset of all stations I selected as “world class” by criteria) are telling us about climate change over the long term. There are three principle findings.

To be included, a station needed at least 200 years of continuous records up to the present. Geographical location was not a criterion for selection, only the quality and length of the histories. 247 years is the average length of service in this dataset extracted from CRUTEM4.

The 25 stations that qualified are located in Russia, Norway, Denmark, Sweden, Netherlands, Germany, Austria, Italy, England, Poland, Hungary, Lithuania, Switzerland, France and Czech Republic. I am indebted to Richard Mallett for his work to identify the best station histories, to gather and format the data from CRUTEM4.

The Central England Temperature (CET) series is included here from 1772, the onset of daily observations with more precise instruments. Those who have asserted that CET is a proxy for Northern Hemisphere temperatures will have some support in this analysis: CET at 0.38°C/Century nearly matches the central tendency of the group of stations.

1. A rise of 0.41°C per century is observed over the last 250 years.

Area WORLD CLASS STATIONS
History 1706 to 2011
Stations 25
Average Length 247 Years
Average Trend 0.41 °C/Century
Standard Deviation 0.19 °C/Century
Max Trend 0.80 °C/Century
Min Trend 0.04 °C/Century

The average station shows an accumulated rise of about 1°C over the last centuries. The large deviation, and the fact that at least one station has almost no warming over the centuries, shows that warming has not been extreme, and varies considerably from place to place.

2. The warming is occurring mostly in the coldest months.

The average station reports that the coldest months, October through April are all warming at 0.3C or more, while the hottest months are warming at 0.2C or less.

Month °C/Century Std Dev
Jan 0.96 0.31
Feb 0.37 0.27
Mar 0.71 0.27
Apr 0.33 0.28
May 0.18 0.25
June 0.13 0.30
July 0.21 0.30
Aug 0.16 0.26
Sep 0.16 0.28
Oct 0.34 0.27
Nov 0.59 0.23
Dec 0.76 0.27

In fact, the months of May through September warmed at an average rate of 0.17C/Century, while October through April increased at an average rate of 0.58C/Century, more than 3 times higher. This suggests that the climate is not getting hotter, it has become less cold. That is, the pattern suggests milder winters, earlier springs and later autumns, rather than hotter summers.

3. An increase in warming is observed since 1950.

In a long time series, there are likely periods when the rate of change is higher or lower than the rate for the whole series. In this study it was interesting to see period trends around three changepoints:
1.1850, widely regarded as the end of the Little Ice Age (LIA);
2.1900, as the midpoint between the last two centuries of observations;
3.1950 as the date from which it is claimed that CO2 emissions begin to cause higher temperatures.

For the set of stations the results are:

°C/Century Start End
-0.38 1700’s 1850
 0.95 1850 2011
-0.14 1800 1900
 1.45 1900 1950
 2.57 1950 2011

From 1850 to the present, we see an average upward rate of almost a degree, 0.95°C/Century, or an observed rise of 1.53°C up to 2011. Contrary to conventional wisdom, the aftereffects of the LIA lingered on until 1900. The average rate since 1950 is 2.6°C/Century, higher than the natural rate of 1.5°C in the preceding 50 years. Of course, this analysis cannot identify the causes of the 1.1°C added to the rate since 1950. However it is useful to see the scale of warming that might be attributable to CO2, among other factors.

Conclusion

Of course climate is much more than surface temperatures, but the media are full of stories about global warming, hottest decade in history, etc. So people do wonder: “Are present temperatures unusual, and should we be worried?” In other words, “Is it weather or a changing climate?” The answer in the place where you live depends on knowing your climate, that is the long-term weather trends.

Note: These trends were calculated directly from the temperature records without applying any adjustments, anomalies or homogenizing. The principle is: To understand temperature change, analyze the changes, not the temperatures.

Along with this post I provide below the World Class TTA workbook for readers to download for their own use and to check the data and calculations.

World Class TTA

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3 comments

  1. Before and after 1950 is interesting. But I was just reading a paper on the AMO that identified the most relevant warming periods as 1910-1940 & 1970-2000, with 1940-1970 a cool phase. ( Kravtsov, et al. 2014)

    It seems that a second post featuring these 30-year periods might show the influence of the AMO.

    As evidence I cite Hubert Lamb’s observation, “In fact, from about the beginning of this century up to 1940 a substantial climatic change was in progress, but it was in a direction which tended to make life easier and to reduce stresses for most activities and most people in most parts of the world. Average temperatures were rising, though without too many hot extremes, and they were rising most of all in the Arctic where the sea ice was receding. Europe enjoyed several decades of near-immunity from severe winters, and the variability of temperature from year to year was reduced. More rainfall was reaching the dry places in the interiors of the great continents (except in the Americas where the lee effect, or ‘rain-shadow’, of the Rocky Mountains and the Andes became more marked as the prevalence of westerly winds in middle latitudes increased).
    End of quote.

    Belda et al (2014) confirmed Lamb’s remark, possibly unintentionally. The study is probably the best to date in reconstructing the Koppen-Trewartha climate classification map for the reasons justifiably claimed by the authors. The maps show the climate regions of the world (except Antarctica) for two periods, 1901-1931 and 1975-2005, based on a 30 minute grid, average area about 2500 km2, (About 50,000 grid cells cover 135 million km2, the land area of the Earth except Antarctica.)

    My analysis of the paper revealed that between the two periods, about 8% of the cells changed climate type. When I plotted a scatter diagram of distributions for the two periods, I found there was little divergence from the straight line passing through the origin and with slope unity. R-squared is 99.5.

    The periods chosen correspond almost the phases of the AMO.

    References:

    Climate, History and the Modern World H. H. Lamb Edition 2, iRoutledge, 1995

    Kravtsov,S., Wyatt, M. G., Curry, J. A., & Tsonis, A. A. (2014). Two contrasting views of multidecadal climate variability in the 20th century. Geophysical Research Letters, 2014
    https://pantherfile.uwm.edu/kravtsov/www/downloads/KWCT2014/DOC_AND_PDF/KWCT2014_PREVIOUS_VERSIONS_AND_REVIEWS/KWCT2014_main_FINAL1.pdf

    Belda, M., Holtanová, E., Halenka, T. and Kalvová, J., 2014. Climate classification revisited: from Köppen to Trewartha. Climate research, 59(1), pp.1-13.
    Paper: http://www.int-res.com/articles/cr_oa/c059p001.pdf

    Like

  2. Ron Clutz · May 7

    Thanks for commenting and for those links. Those periods linked to AMO do show up strongly in Wijngaarden 2015, which included most of these stations and then some.

    Like

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