Applying Ockham's Razor to human-induced global warming hypotheses

For the benefit of those who may not be aware, William of Occam (?1280-?1348) was an English philosopher. His revered "Ockham's Razor," is a guide to clear thinking that states, perhaps opaquely: "Multiplicity ought not to be posited without necessity." In science, that is expressed: "When more than one explanation of a phenomenon is offered, the simplest explanation is probably the most accurate one."

Given that there are just two hypotheses of anthropogenic (caused by human action) global warming, it should not be too difficult to apply Ockham's Razor. To determine which of the hypotheses is most likely correct, we need only determine which is the more complex (least likely) and discard it.

Hypothesis 1: the enhanced greenhouse effect.

Loosely stated, the enhanced greenhouse hypothesis postulates that increase in the atmospheric levels of the minor so-called greenhouse gases - those capable of absorbing infrared radiation (IR) - will cause warming of the atmosphere, which, in turn, could lead to a warming of the planetary surface.

The so-called greenhouse effect is real, without its natural occurrence Earth would be a lifeless -16°C and below.

Human activity is releasing greater quantities of the minor greenhouse gases to atmosphere than had been observed to occur naturally in Earth's recent past. The most significant increase is liberation of carbon dioxide (CO₂) due primarily to combustion of fossil fuels. Next most significant is methane (CH₄), although rate of increase is now negligible and it is expected to be in atmospheric equilibrium (as much consumed as produced) in 2004.

Here, the scenario must unfortunately increase in complexity for the IR absorbency of the known increase in minor greenhouse gases cannot be reconciled with the apparent increase in measured surface temperature. This is a little like wanting to heat your coffee to 75°C in a convection oven at 50°C for, if the atmosphere can contain only enough energy to raise it to say, +16°C, how could it induce +20°C at the planet's surface? To overcome this dreadful shortfall, the concept of positive feedback must be introduced.

Positive feedback postulates that the small increase in atmospheric temperature possible from observed increase in minor greenhouse gases must somehow be amplified in order to fit the desired scenario. Here we introduce the one truly significant greenhouse gas, water vapour, responsible for nine-tenths of Earth's greenhouse effect. First, we postulate that small increases in minor greenhouse gases induce sufficient, although admittedly minute, warming to increase evaporation and the production of clouds. Care, however, is still required because, while cirrus (high, thin cloud) exhibits a warming influence by absorbing IR in the wavelengths emitted by Earth but less so the shorter wavelengths arriving from the sun, cumulus (the white, fluffy clouds lower in the atmosphere) reflect solar energy (albedo) and are a cooling influence. Positive feedback requires that increase in the minor greenhouse gases induce an increase (but not too much) in upper atmospheric water vapour while maintaining (or, better still, reducing) lower atmospheric water vapour constituents.

While we now have a postulated mechanism to accommodate the desired result there are other inconvenient observations that must be taken into account. Principal among these are balloon sonde and satellite-mounted microwave sounding unit measures which demonstrate that the atmosphere is not warming in accord with model predictions. Enter the sulfate aerosol and particulate hypotheses. Briefly stated, these reflective particles are assumed to increase albedo, thus masking the atmospheric warming that would otherwise be apparent. How an atmosphere that is being warmed by enhanced greenhouse, while being cooled by particulate albedo, thus not warming after all, could be responsible for surface warming is not addressed. Convection and atmospheric mixing are simply too complex and are ignored altogether.

In abbreviated form and greatly simplified, this is the enhanced greenhouse hypothesis.

Hypothesis 2: urban heat island (UHI)-induced measurement error.

The Urban Heat Island effect is well demonstrated and can be confirmed by any group who wish to calibrate their thermometers (by simply measuring ambient temperature at a common location at a common time and determining a common measure) and subsequently measuring city and surrounding regional temperature at common times - 99 times out of 100 urban centres record significantly higher temperatures. As far back as 1973, Oke (City size and the urban heat island. Atmospheric Environment 7: 769-779) demonstrated a linear correlation with the logarithm of the urban population. With as few as 1,000 inhabitants, urban centres demonstrate local temperature perturbations of +2°C - +2.5°C (twice as large as the total estimated increase for the twentieth century). A metropolis such as "Hotlanta" can record local ambient increases in the +10°C range and beyond.

The UHI-induced measurement error hypothesis postulates that, by closure of rural recording stations and increasing reliance on measures taken within growing urban centres, we have 'screwed-up' our surface record.

This hypothesis does not require reconciliation between observed urban warming and negligible atmospheric warming observed in balloon sonde and satellite-mounted MSU records since the latter two are not subject UHI and so not expected to be affected.

Hypothesis 1, the enhanced greenhouse effect, requires feedback amplification and supportive hypotheses to both warm and cool the atmosphere so that the surface can be warmed by a warming atmosphere but the atmosphere to be cooled so that the warming is masked [!] Humans screwed-up and are cooking the planet by convoluted physical and chemical effects that can not be demonstrated.

Hypothesis 2, urban heat island (UHI)-induced measurement error, requires only the empirically demonstrated urban heat island effect. Humans screwed-up by making a mess of the temperature record.

Both hypothesis indicate human-induced global warming, one physical, one illusory.

What do you suppose William of Occam would have made of our hypotheses, one highly complex and devoid of empirical support and the other simple and demonstrable?