In previous post I concluded with the remark that probability theories are not falsifiable in a strict true|false way, but they can be seen as competing theories that can be compared. The theory that makes the clearest predictions of future outcome and that describes best previous and current observations, will be more preferable. Maybe this was a bit an abrupt ending, so I will explain a bit more in this post. Especially the Global Warming theory against one competing theory: the Natural Cycle theory.
First, let’s look at some long term measurements of temperatures. Below the Giss dataset, starting from 1880 (figure 1).
I will accentuate some trends on this graph to explore the two theories. The lines were made with a simple graphic editor, so they don’t pretend high accuracy. They are drawn to give some indication of trends or, more accurate, how trends are perceived.
The global warming theory
The Global Warming Theory claims that we put ever increasing amounts of CO2 from burning fossil fuel in the atmosphere. CO2, being a greenhouse gas is the major driver for the temperature increase. It is a plausible theory and can explain a lot. At first glance one could easily deduce that man and industrialization has caused global warming (figure 2). It explains the increase of temperatures, especially the warming at the end of the 20th century (which is perfectly in line with the CO2 increase at that time).
Figure 2: Representing Global Warming
But it doesn’t explain very well the warming in the first half of the 20th century. There was not much CO2 added in the atmosphere yet (CO2 started to pick up speed in the second half of the century), so this warming supposed to be of natural cause. But after this the temperature was decreasing or stayed the same when more CO2 was “spewed” in the atmosphere. Compared the warming of the first half to the warming of the second, which has the same increase (figure 3), but this time it is supposed to be primarily of anthropogenic cause.
Figure 3: Parallel warming begin and end 20th century
It also doesn’t explain very well the stagnation of the last 10+ years in which there was more CO2 in the atmosphere than ever before. If CO2 is the major driver of the temperature increase this stagnation doesn’t fit very well. In that case one would expect there is a driver (or a set of drivers) that is as strong as CO2.
The natural cycles theory
The Natural Cycle theory claims that the earth is warming and cooling in cycles. There are cycles of about 30 years, but there are also other cycles that are longer, like 300-500 years. The last one was called Little Ice Age (of about 500 years) and followed the Medieval Warm period (of about 400 years).
Figure 4: Representing Cycles
When one looks at the graph from 1880, the temperature doesn’t increases gradually, but one can see regular shifts in which there are increases followed by decreases or stagnations (figure 4). It explains the cooling until the 1910s, the next 30 years a warming, the next 30 years a small decrease/stagnation, the next 30 years a warming. Next, according to the theory the current stagnation should not be a surprise at all and even could last for some decades.
But doesn’t CO2 has an effect then? Of course it does. As a greenhouse gas, everything else being equal, it will give some warming if there is more of it. But it is not necessarily the major driver as assumed in the Global Warming theory.
But doesn’t the graph show a large upward trend? The upward parts are way larger than the downward/stagnation parts. True, but this probably has more to do with the scale of the Y-axis. Expand the scale and warming will seem to go trough the roof. Compress it and the warming will seem unimpressive.
But what about the increase itself? According to the graph there is an temperature increase of about 0.8 °C over the last 130 years. Isn’t that reflecting the industrialization of our society? Could well be, but we came out of a cold period around 1850 (end of the Little Ice Age). If the last large (cold) cycle was about 500 years in length, then a 130 year of warming shouldn’t be that unusual…
Of course this doesn’t prove anything. But it gives an indication that the recorded warming can be explained otherwise or, well, let’s say is also “consistent with” other theories. The global warming theory is not the only theory that can explain the temperature increase in the last 130 years. It shows that there is at least one other competing theory that is plausible and can be used to compare.