Occam's Razor and Climate Change

The simplest explanation is usually the correct explanation

Guest essay by Eric Worrall

Professor Keven Trenberth once campaigned for the scientific world to accept the alarmist view of climate change as the “null hypothesis”, the baseline theory against which all other theories must be measured.

http://wattsupwiththat.com/2011/11/03/trenberth-null-and-void/

The reason Trenberth faced an uphill battle to have his view accepted, and ultimately failed, is that the simplest explanation of contemporary climate change does not involve Anthropogenic CO2.

As Professor Phil Jones of the CRU once admitted in an interview with the BBC, the instrumental record contains periods of warming which are statistically indistinguishable from the 1990s warming – periods of warming which cannot have been driven by anthropogenic CO2, because they occurred before humans had made a significant changes to global CO2 levels.

Between 1860 and 1880, the world warmed for 21 years, at a similar rate to the 24 year period of warming which occurred between 1975 and 1998. There was simply not enough anthropogenic CO2 in the atmosphere to have driven the 1860s warming, so it must have been driven by natural variation.

So how does Occam’s Razor apply to this observation? 

According to the definition in Wikipedia, the principle of Occam’s Razor states “that among competing hypotheses, the one with the fewest assumptions should be selected. Other, more complicated solutions may ultimately prove correct, but—in the absence of certainty—the fewer assumptions that are made, the better.”

From Wikipedia, the reason why Occam’s razor is important:

“To understand why, consider that, for each accepted explanation of a phenomenon, there is always an infinite number of possible, more complex, and ultimately incorrect alternatives. This is so because one can always burden failing explanations with ad hoc hypothesis. Ad hoc hypotheses are justifications that prevent theories from being falsified. Even other empirical criteria like consilience can never truly eliminate such explanations as competition. Each true explanation, then, may have had many alternatives that were simpler and false, but also an infinite number of alternatives that were more complex and false. However, if an alternate ad hoc hypothesis were indeed justifiable, its implicit conclusions would be empirically verifiable. On a commonly accepted repeatability principle, these alternate theories have never been observed and continue to not be observed. In addition, we do not say an explanation is true if it has not withstood this principle.

Put another way, any new, and even more complex theory can still possibly be true. For example: If an individual makes supernatural claims that Leprechauns were responsible for breaking a vase, the simpler explanation would be that he is mistaken, but ongoing ad hoc justifications (e.g. “And, that’s not me on film, they tampered with that too”) successfully prevent outright falsification. This endless supply of elaborate competing explanations, called saving hypotheses, cannot be ruled out—but by using Occam’s Razor.”

Source: http://en.wikipedia.org/wiki/Occam’s_razor

In other words, if we reject the principle of Occam’s Razor, we open the door to accepting theories of arbitrary, ultimately infinite complexity. A theory created by researchers who do not accept the principle of Occam’s Razor cannot be falsified, because the theory can always be tweaked in arbitrary ways to avoid falsification.

So why does applying the principle of Occam’s Razor force us to reject the theory that anthropogenic CO2 is the main driver of contemporary climate change? The reason is that nature has produced periods of warming similar to the recent warming, without any significant contribution from Anthropogenic CO2.

So we have two competing hypothesis for what is driving contemporary climate change:-

1. Observed natural variation, which has produced periods of warming statistically indistinguishable from the warming which ended in 1998.

2. Observed natural variation + an unproven assumption that Anthropogenic CO2 is now the main driver of Climate Change.

Clearly the second hypothesis fails the test of Occam’s Razor. In the absence of compelling evidence that anthropogenic CO2 has overridden natural variation, we have to accept hypothesis 1 – that observed climate change is the result of natural variation.

The climate is not hotter than it was in the past, periods such as the Holocene Optimum, or looking further back, the Eemian Interglacial. The warming which ended in 1998 was not faster, or of significantly longer duration, than similar natural warmings which occurred in the recent past.

Nothing about the current climate is outside the bounds of climatic conditions which could reasonably be produced by natural variation – therefore, according to the rules of science, we have to reject hypothesis which unnecessarily embrace additional unproven assumptions, unless or until such assumptions can be tested and verified, in a way which falsifies the theory that natural variation is still in the driver’s seat.