MORE ON CHARTSMANSHIP

Last Saturday John Ray posted a blog regarding deceptive chartsmanship purporting to show man cause global warming. Since some people put a great deal of faith in these charts and don’t understand the difficulties that they present, I thought I would try to demonstrate some of the problems in relying on informational charts.

First, let’s take a look at the GISS chart John posted.

The graph shows a sharp increase in temperature since 1880, however, notice that the temperature scale only goes from -0.4°C to 0.6°C or just 1°C. Keep in mind, at the moment I’m not discussing whether or not 1°C is something to worry about, but rather the impression one gets from a chart. And in this case the chart looks like things are really getting hot. But let’s take that same chart and just resize it a little.

By simply compressing the y-axis and stretching the x-axis I’ve created a chart where the upward slope is much more gradual. But what would happen if I changed the minimum and the maximum on the y-axis (temperature) scale? To do this, I took the GISS chart above and recreated it in MS Excel using a temperature from approximately every fifth year. (My chart is only an eyeball estimate of some of the values in the GISS chart and is not accurate, it is only intended to demonstrate the problems involved in chart interpretation.) Here is what the chart looks like on approximately the same scale as the original.

Notice that by leaving out some of the data the chart already has a different feel to it, but the general upward trend is maintained. The message of this and the original chart is that temperature is rising dramatically. Now, look at the same chart with a 50°C + or – scale representing something similar to global extremes in temperature.

The message of this chart is that there is no change in temperature. Of course, using the extremes would be deceptive in its own right, but even dropping the scale from 50°C to 5°C does little to change the impression of no temperature increase.


Only when we get the scale down to 1°C do we start to see any appreciable rise in temperature.

An additional aspect to notice is the very short time span. The earth is billions of years old, but only a miniscule 120 years is shown in the chart. Such a short time span would be insignificant to demonstrate an unusual warming pattern. In fact, if we look at a longer time span we find that the earth has been warmer many times in the past. In the case of the GISS graph, the designer deliberately chose a scale and segment of time that overly amplified the warming affect and hid the fact that the warming is relatively minor and normal. Essentially, the chart is taken out of context.

The point here is that one can use the same data to convey completely different results to the viewer, simply by choosing the proper scaling properties of the graph. This technique can be used with great success, especially when the charts are presented to an audience that is not sufficiently educated in the subject being discussed (or not careful enough to notice). Take for example, the infamous “hockey stick” graph used by Al Gore and the IPCC to show that CO2 was causing dangerous global warming. The graph had significant impact on audience’s world wide, and the fact that the data had been manipulated as well only increased its impact (See, "The IPCC, the "Hockey Stick" Curve, and the Illusion of Experience", for a discussion of the graph.).

Many of the graphs used by proponents of Global Warming share a characteristic in that they are designed to highlight a warming trend and depict it as drastic, while downplaying or leaving out trends that would indicate otherwise. In the “hockey stick” graph (blue) the data left out the medieval warming period. The red line shows a corrected version with the medieval warming period included. And as expected, the two plots tell completely different stories. The blue plot says that something very unusual began in the 20th century. The red shows that the warming was not unusual and not nearly as drastic as had occurred in the past. Notice that if one could take just the data from 1600 to the present from either plot he could still make it appear that something bad was happening after 1900.

Ibid. p. 4

Believing Can Hurt.

As you can see, these charts can easily be manipulated to convey a desired message, even a false message, to a given audience. But charts can convey a false message even when there is no intent to mislead. Take for an example the 1986 Challenger Space Shuttle disaster. Prior to the launch there was a concern that the O-rings used to join the booster rocket sections would shrink in the cold weather and not properly seal the joints between the sections during a launch, allowing the hot gasses to “blow through” the rocket walls. The engineers at Morton-Thiokol knew this and met with NASA management to argue for a postponement of the launch, since the temperature was expected to be in the mid 20s °F. In doing so, they presented the following chart showing the flights with o-ring failures and the number of failures per flight.

The managers looked at the chart and concluded that joint failures were something that was part of flying the shuttle and didn’t pose an unusually risk. After all, it happened at all temperatures. But look at the story told by the next chart that the managers didn’t see, which included the flights that did not have any failures.

The difference is immediately obvious; the only flights that had no failures took place in temperatures above 65°F. Anything below that was assured to have an o-ring failure, and the temperature for the launch was lower than any attempted previously. The engineers that were closest to the problem understood the graph and took it for granted that others would too. But had the managers seen the second chart, it is very likely that their decision would have been to wait for warmer weather.

The point of all this is that charts do not always tell the truth. They can be helpful tools, but it is often necessary to look more closely at the chart, the data, and even the methodology behind it in order to make a valid decision as to whether it is trustworthy. This is something that many people, particularly global warming enthusiasts, do not do, and the consequences can be quite dire.