Guest essay by Ron Clutz
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|
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 0.3°C or more, while the hottest months are warming at 0.2°C or less.
In fact, the months of May through September warmed at an average rate of 0.17°C/Century, while October through April increased at an average rate of 0.58°C/Century, more than 3 times higher. This suggests that the climate is not getting hotter, it has become less cold..
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 breakpoints:
- 1850, widely regarded as the end of the Little Ice Age (LIA);
- 1900, as the midpoint between the last two centuries of observations;
- 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:
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.
Of course climate is much more than surface temperatures, but the media are full of stories about global warming, hottest decade or month 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 any use of adjustments, anomalies or homogenizing. The principle is: To understand temperature change, analyze the changes, not the temperatures.
Along with this post I have submitted the World Class TTA Excel workbook for readers to download for their own use and to check the data and calculations. You can download it from this link: World Class TTA (.xls)
For those who might be interested, the method and rationale are described at this link, along with the pilot test results on a set of Kansas stations: