The global average temperature is a calculated number based on stations on land, with some observations over the oceans and each station represents the temperature over wide areas of earth. The calculations of global temperature since 1880 have moved less than the distance on a thermometer that represent 2 degrees F. There are many problems with the calculated global average temperature that need to be considered. Sites with temperature readings will be opened and closed, and sites may be moved.   Missing data are often a problem at the sites. Over time, the surroundings of the site may change and will change the temperature. Changes in instrumentation may result in changes in temperature when accuracy is increased. Some of the remote sites have a large weight in assessing small changes and any inaccuracies at the sites would be magnified.

Problem 1. Site Changes. Known site changes are generally considered in computing long-term averages at a given site. A move to a new location often can be accounted for in the analysis. However, the surroundings at a site that remains stationary may change and be undocumented. Examples of some of the issues include thermometers in parking lots, near building exhausts and developments that change the settings from rural to urban. And these were within the U.S., where the measurements are assumed to be better. These changes certainly compromise the data when dealing with small differences of the temperature being examined over long periods of time. In a study of the climate stations in the U.S., only about 10 per cent of the stations were considered excellent and 70 percent were called highly inaccurate due to siting issues at the stations. The rate of increase at the excellent stations was smaller than the rate observed at the stations with siting issues.

Problem 2. Urbanization. Many of the sites experienced increased urban development near the individual site that gave rise to an ‘urbanization’ effect with an increased temperature over time. This would result in an increased warming trend nearer the end of the period. With the rapidly increasing population and the expansion of the cities, the urban heat island may be affecting more sites. And recent studies have shown increase warming even with the addition of new buildings near the thermometer.

Problem 3. Data Manipulation.   Numerous adjustments have been made in the algorithms to the global average temperatures in the past few years. In some of the computations adjustments are made to “correct” for the changes in the urban heat island effect in the past century. However, anecdotal evidence have been shown over the years that show the earlier parts of the 20^th century are cooler now than reported several years earlier, thereby making it appear the warming is more pronounced.

In order to update the GISS global temperature table for the past five years, I downloaded the table recently that gave the data since 1880. The resultant graph showed cooler temperatures than previously reported in the 1940s. So a comparison was made between the 2015 table and the 2010 table. The differences are shown in the figure. All changes toward cooling occur before 1977 with the largest in the 1940s. Considering that the magnitude of the 20^th century increase is about 1°C, the adjustments contribute a portion of the increase. It also leads to the question as to whether the global temperature computed from surface stations is a good measure of climate change or whether it just becomes a part of the government side of the global warming controversy.

 Problem 4. Seasonal differences.   Several studies have shown that the period October through April are warming faster than the May to September period. Also the polar regions seem to be warming faster than the tropics or mid latitudes. This suggests that the climate is not getting hotter, it has become less cold. This is somewhat contradictory to the direct cause being carbon dioxide in that the downward flux due to carbon dioxide is reduced during higher CO2 when inversion conditions exist. This winter warming seems to be a benefit with a lowering of energy requirements.   And what makes people think the climate around 1900 (or any other year) represents the ideal?

Problem 5. Reason for the Changes.   The main problem is how much of the warming can be attributed to Man’s emission of carbon dioxide in Figure 4. How is the warming of the past 50 years any different from the warming from 1910 to 1940, which the IPCC attributed to ‘natural causes?’ The temperature increase from 1970-2000 was attributed by the IPCC to be the result of the increasing CO2. And why did the warming stop around 2000, even though carbon dioxide continued to increase. And how much of the warming occurs from a ‘reanalysis’ of the temperature in recent years.

It is difficult to determine accuracy of the computed global temperature averages. In general, the temperature has increased over two 20-30 year periods in the last century with minimal changes since 2000. The IPCC attributes the increase in the second period as being caused by the increase in carbon dioxide concentrations.