Posted on 22 September 2010 by
Guest post by Alan Marshall from climatechangeanswers.org
Update August 9, 2020: Please be aware that this article was published in 2010 and that its content is no longer considered accurate. As it still gets regularly linked to from other websites, we will not delete or “unpublish” it. Instead, here is the link to a better take on this topic published by our late team member Andy Skuce in 2013: Global Warming: Not Reversible but Stoppable.
Following the failure to reach a strong agreement at the Copenhagen conference, climate skeptics have had a good run in the Australian media, continuing their campaigns of disinformation. In such an atmosphere it is vital that we articulate the basic science of climate change, the principles of physics and chemistry which the skeptics ignore.
The purpose of this article is to clearly explain, in everyday language, the two key principles which together determine the rate at which temperatures rise. The first principle is the greenhouse effect of carbon dioxide and other gases. The second principle is the thermal inertia of the oceans, sometimes referred to as climate lag. Few people have any feel for the numbers involved with the latter, so I will deal with it in more depth.
The Greenhouse Effect
The greenhouse effect takes its name from the glass greenhouse, which farmers have used for centuries, trapping heat to grow tomatoes and other plants that could not otherwise be grown in the colder regions of the world. Like glass greenhouses, greenhouse gases allow sunlight to pass through unhindered, but trap heat radiation on its way out. The molecular structure of CO2 is such that it is “tuned” to the wavelengths of infrared (heat) radiation emitted by the Earth’s surface back into space, in particular to the 15 micrometer band. The molecules resonate, their vibrations absorbing the energy of the infra-red radiation. It is vibrating molecules that give us the sensation of heat, and it is by this mechanism that heat energy is trapped by the atmosphere and re-radiated to the surface. The extent to which temperatures will rise due to a given change in the concentration of greenhouse gases is known as the “climate sensitivity,” and you may find it useful to search for this term when doing your own research.
Most principles of physics are beyond question because both cause and effect are well understood. A relationship between cause and effect is proved by repeatable experiments. This is the essence of the scientific method, and the source of knowledge on which we have built our technological civilization. We do not question Newton’s laws of motion because we can demonstrate them in the laboratory. We no longer question that light and infrared radiation are electromagnetic waves because we can measure their wavelengths and other properties in the laboratory. Likewise, there should be no dissent that CO2 absorbs infrared radiation, because that too has been demonstrated in the laboratory. In fact, it was first measured 150 years ago by John Tyndall [i] using a spectrophotometer. In line with the scientific method, his results have been confirmed and more precisely quantified by Herzberg in 1953, Burch in 1962 and 1970, and others since then.