Anomalies are unsuitable measure of global temperature trends
Guest post by David M. Hoffer
An anomaly is simply a value that is arrived at by comparing the current measurement to some average measurement. So, if the average temperature over the last 30 years is 15 degrees C, and this year’s average is 16 degrees, that gives us an anomaly of one degree. Of what value are anomalies? Are they a suitable method for discussing temperature data as it applies to the climate debate?
On the surface, anomalies seem to have some use. But the answer to the second question is rather simple.
If the whole earth was a single uniform temperature, we’d have no need of anomalies. But the fact is that temperatures don’t vary all that much in the tropics, while variations in the high temperate zones are frequently as much as 80 degrees over the course of a year. How does one compare the temperatures of say Khartoum, which on a monthly basis ranges from an average of 25 degrees to 35 degrees C, to say Winnipeg, which might range from -40 in the winter to +40 in the summer?
Enter anomalies. By establishing a base line average, usually over 30 years, it is possible to see how much temperatures have changed in (for example) winter in Winnipeg Canada versus Khartoum in summer. On the surface, this makes sense. But does the physics itself support this method of comparison?
It absolutely does NOT.
The theory of CO2’s direct effects on earth’s surface temperature is not terribly difficult to understand. For the purposes of this discussion, let us ignore the details of the exact physical mechanisms as well as the order and magnitude of feedback responses. Let us instead assume that the IPCC and other warmist literature is correct on that matter, and then see if it is logical to analyze that theory via anomaly data.
The “consensus” literature proposes that direct effects of CO2 result in a downward energy flux of 3.7 watts/m2 for a doubling of CO2. Let’s accept that. Then they propose that this in turn results in a temperature increase of one degree. That proposal cannot be supported.
Let us start with the one degree calculation itself. How do we convert watts/m2 into degrees?
The answer can be found in any text book that deals with radiative physics. The derivation of the formula requires some in depth understanding of the matter, and for those that are interested, Wikipedia has as good an explanation as we need:
For the purposes of this discussion however, all we need to understand is the formula itself, which is:
It took Nobel Prize winning work in physics to come up with that formula, but all we need to use it is a calculator.
For the mathematically inclined, the problem ought to be immediately obvious. There is no direct correlation between w/m2 and temperature. Power varies with T raised to the power of 4. That brings up an obvious question. At what temperature does the doubling of CO2 cause a rise in temperature of one degree? If we use the accepted average temperature of earth surface as +15 degrees C (288 degrees K) simply applying the formula suggests that it is NOT at the average surface temperature of earth:
For T = 288K
P = 5.67*10^-8*288^4 = 390.1
For T = 289K (plus one degree)
P = 5.67*10^-8*289^4 = 395.5
That’s a difference of 5.4 w/m2, not 3.7 w/m2!
So, how does the IPCC justify their claim? As seen from space, the earth’s temperature is not defined at earth surface, nor can it be defined at the TOA (Top of Atmosphere). Photons escaping from earth to space can originate at any altitude, and it is the average of these that defines the “effective black body temperature of earth” which turns out to be about -20 C (253 K), much colder than average temperatures at earth surface. If we plug that value into the equation we get:
253K = 232.3 w/m2
254K = 236.0 w/m2
236.0 – 232.3 = 3.7
There’s the elusive 3.7 w/m2 = 1 degree! It has nothing to do with surface temperatures! But if we take this analysis a step further, it gets even worse. The purpose of temperature anomalies in the first place was supposedly to compare temperature changes at different temperature ranges. As we can see from the analysis above, since w/m2 means very different things at different temperature ranges, this method is completely useless for understanding changes in earth’s energy balance due to doubling of CO2.
To illustrate the point further, at any given time, some parts of earth are actually in cooling trends while others are in warming trends. By averaging temperature anomalies across the globe, the IPCC and “consensus” science has concluded that there is an overall positive warming trend. The following is a simple example of how easily anomaly data can report not only a misleading result, but worse, in some cases it can report a result the OPPOSITE of what is happening from an energy balance perspective. To illustrate, let’s take four different temperatures and consider their value when converted to w/m2 as calculated by Stefan-Boltzmann Law:
-38 C = 235K = 172.9 w/m2
-40 C = 233K = 167.1 w/m2
+35 C = 318K = 579.8 w/m2
+34 C = 317K = 587.1 w/m2
Now let us suppose that we have two equal areas, one of which has an anomaly of +2 due to warming from -40 C to -38 C. The other area at the same time posts an anomaly of -1 due to cooling from +35 to +34.
-38 C anomaly of +2 degrees = +5.8 w.m2
+35 C anomaly of -1 degree = -7.3 w/m2
“averaged” temperature anomaly = +0.5 degrees
“averaged” w/m2 anomaly = -0.75 w.m2
The temperature went up but the energy balance went down? The fact is that because temperature and power do not vary dirfectly with one another, averaging anomaly data from dramaticaly different temperature ranges provides a meaningless result.
Long story short, if the goal of measuring temperature anomalies is to try and quantify the effects of CO2 doubling on earth’s energy balance at surface, anomalies from winter in Winnipeg and summer in Khartoum simply are not comparable. Trying to average them and draw conclusions about CO2′s effects in w/m2 simply makes no sense and produces a global anomaly that is meaningless.