Global warming caused by conduction, not radiation

02 Jun 2007 Global warming caused by conduction, not radiation

I regularly listen to a podcast from Australia’s ABC Radio National called Occam’s Razor. One particular episode, featuring Professor Emeritus Duncan Brown from the Department of Biological Sciences, University of Wollongong, has stuck in my mind, and I’d like to include some of it here. The link for the entire podcast with transcripts is: http://www.abc.net.au/rn/ockhamsrazor/stories/2005/1497147.htm

Here is what I found particularly interesting – the rest of this post is a long quote from Dr. Brown:

In this talk I shall try to put the environmental problems that we face into some sort of perspective. Serious environmental problems are widely acknowledged. They are mostly identified as specific challenges, such as deforestation, soil and water degradation, loss of biodiversity, and of course, global warming. The essence of my argument is that all of these challenges, while very serious, are actually symptoms of a much more dangerous predicament, a human population that is too large and too dependent on technology to be sustainable.

But let me begin with some comments on global warming, the symptom that currently seems to receive most attention and is discussed almost entirely in the context of the ‘greenhouse effect’. This is an interesting example of widespread acceptance of a conventional wisdom while other more significant factors are largely overlooked or ignored.

To simplify: the earth’s average atmospheric temperature is estimated to have risen by about 0.6 degrees Celsius over the past century. This heating is attributed predominantly to absorption by carbon dioxide of infrared radiation. The current average atmospheric concentration of carbon dioxide is estimated to be 372 parts per million, thought to be the highest for at least 420,000 years. But water also absorbs infrared radiation, and there is much more of that in the atmosphere than there is of carbon dioxide.

Many factors have contributed to heating the atmosphere since the advent of agriculture. They include major changes to the earth’s surface, especially deforestation with its associated loss of cooling by ‘evapotranspiration’; the growth of cities, which are recognised as ‘urban heat islands’; an increase in the total biomass of mammals; and most significantly, the heat produced by enormous increases in rates of combustion.

The quantity of so-called ‘fossil’ carbon burnt in 2003 amounted to some 6 Giga tonnes. Fossil carbon occurs in a wide range of substances which are not identified in that statistic; but to oversimplify and assume for example that it was distributed equally among anthracite coal and three significant components of motor fuel: pentane, hexane and decane, the heat produced amounted to 74 billion Giga calories for the year. Ignoring a range of atmospheric variables which are virtually impossible to quantify, that amount of heat has the capacity to raise atmospheric temperature by 0.06 degrees Celsius annually. Variables or not, that would seem to be enough to make a very substantial contribution to an increase of 0.6 degrees Celsius over a century. And that takes no account of other significant types of combustion, such as bushfires.

One of the curious aspects of the overwhelming focus on carbon dioxide and the ‘greenhouse effect’ is that it attributes the heating process entirely to radiation and ignores direct heating by contact and conduction. Of course primary solar heating occurs by radiation and heat is lost from the planet by radiation. But much, and indeed probably most of the heat transfer within the planet’s boundaries involves conduction. Carbon dioxide at its present concentration is irrelevant to direct heating of the atmosphere in that way.

The focus on greenhouse gases would not matter at a practical level if it led to a reduction in overall combustion. But if it provokes chemical binding of carbon dioxide, or its geosequestration, which amounts to burying it underground, or the use of alternative fuels such as hydrogen, the primary heating problem will not be addressed and there will certainly be a range of disturbing, unintended consequences.