Guest essay by Tim Crome

The plots attached here are taken from the MOYHU blog maintained by Nick Stokes here. The software on the blog allows the global temperature anomaly data for each month for the last several years, it also allows the mesh showing the temperature measurement points to be turned on and off.

This is a powerful tool that gives excellent opportunities to plot the temperature anomalies around the globe. Looking at the mesh used in the plotting routines does however raise some questions.

Figure 1 shows the data for the month of October 2017 centred on the East coast of Greenland. It shows that the whole of Greenland has an temperature anomaly that is relatively high. What becomes apparent when the mesh is turned on is that this is purely the result of the density of measurement points and the averaging routines used in generating the plots. This can be seen in Figure 2, zoomed in on Greenland.

Figure 2 shows the same data as Figure 1 but with the addition of the mesh and data points. If we study Greenland it is very apparent that the temperature on the surface of most of the inland ice is, in this model, determined by one measurement point on the East coast of the country and a series of points in the middle of the Baffin Bay between the West coast of the country and North East Canada, no account is taken of the temperatures of the interior of Greenland, often significantly below those occurring along the coastline.

Figure 2 also shows how there is a large part of the Arctic Ocean without any measurement points such that the few points around the circumference are effectively defining the plotted values over the whole area.

Similar effects can also be seen at the Southern extremities of the planet, as shown in Figure 3. There are only two points on the interior of Antarctica and relatively few around the coast. For most of the East Antarctic Peninsula, about which we often hear stories of abnormal warming, there is clearly a situation where the temperature anomaly plots are developed from one point close to the South Pole and two locations some distance out at sea North of the peninsular. This cannot give an accurate impression of the true temperature (anomaly) distribution over this sensitive area.

Another geographical region with very few actual measurements, and huge distances over which the data is averaged, is Africa, as shown in Figure 4. There is a wide corridor from Egypt and Libya on the Northern coast to South Africa with absolutely no data points, where the averages are determined from relatively few points in the surrounding areas. The same is also true for most of South America and China (where the only data points appear to be in the heavily populated areas).

Based on this representation of the data it is apparent that there are huge areas where the scarcity of data and the averaging routines will give incorrect results. Often the temperature anomaly distribution in these areas, especially for Greenland and the Eastern Antarctic Peninsula, is used to show that these sensitive areas of the globe are subject to extraordinary warming threatening our very way of life. Such conclusions are invalid, they are purely the result of a scarcity of good data and statistical practices.

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