Sunday, June 09, 2002
GLOBAL WARMING - MYTH OR GLOBAL DISASTEROUS TERROR?
I feel I must state my take on this controversial issue. Firstly one must address the "Global Warming" stated in the title. This is a term often touted by the tabloid press in order to generate revenue, as is their shock tactics wont of late. This term is highly inaccurate from a climate point of view. There is no question of "Global Warming". The preferred term for the layman is "The Greenhouse Effect", whereby the atmospheric composition is altered, with increased amounts of insulating gasses in particular.
In order to give a reasoned judgement on the state of climate change, one must isolate the issues involved. The main concern in this area is the influence of Man, particularly the potential acceleration of the natural climatic cycle of the globe. To ascertain whether the natural climate change is being affected by man, one must be aware of the natural cycle, and where the earth is in the stage of this cycle at present, "the Holocene, which has already lasted 11,000 years, is, by far, the longest stable warm period recorded in Antarctica during the past 420,000 years," according to the Center for the Study of Carbon Dioxide and Global Change (1). Fluctuations of this nature are clearly not a result of the influence of Man.
Natural climatic cycles(2)
The above graph illustrates the instability of the earths climate over the past million years. You may wonder how we could possibly know what the climate was like say 50,000 years ago when we have only been recording climatic data for the past 200 years or so. Climatic data for pre-history periods is invariably inferred from readings taken from ice caps (Greenland for instance), oceanic sediment analysis (analysis of debris dropped by icebergs), and sedimantary rock analysis. These shall be dealt with in turn. It is also apparent that such changes in climate, taking place over periods of several hundred thousand years cannot be a result of the influence of mankind. This is often pointed to as a reason to ignore current climatic trends, however, the question is more to do with the acceleration of the natural fluctuations and the exacerbation of the effects.
One of the most accurate ways to discover past climatic and atmospheric conditions is through the analysis of cores taken from large, stable ice caps. These cores can be taken from great depths, and in general, the thicker the ice cap, the further back in time the record stretches. Other methods of climatological records include tree-rings (both of very old living trees, some approaching 5000 years old, such as the Ancient Bristlecone Pine, California, USA (3), and of preserved tree remains in peat bogs etc.), which provide an indication of climatic conditions through growth rates from year to year. While providing a more accurate chronological record, dendrochronology (tree ring study) does not provide as precise a representation of past climatic conditions as ice-cores, as many factors can influence the growth rate of a tree, not just climatic conditions. Therefore this discussion will focus on the ice-core method of past climatic condition study.
When snow is layed down it traps a small amount of atmospheric gas (air) with it. Over time the snow becomes compacted, turning into ice. In this ice there are bubbles containing small amounts of atmospheric gas forming a record stretching back for the age of the ice cap. The relative proportions of gas in this trapped air can be analysed to give a good indication of climatic conditions at the time they were deposited, particularly temperature. The most widely used indicator gas is Oxygen. Oxygen is present in two main forms, Oxygen16 (making up the bulk of the atmospheric Oxygen), and Oxygen18 (less than 1%). The important point about Oxygen is that the two isotopes evaporate at different rates depending on the temperature at the time. Therefore, by measuring the relative concentrations of these isotopes, one can reconstruct the temperature of the globe at the time.
Further reading and sources:
(1) http://www.co2science.org/journal/1999/v2n12c1.htm - recent climatic fluctuations (geologically speaking).
(2) http://www.co2science.org/subject/other/clim_hist_2million.htm - longer term fluctuations in climate.
(3) http://www.sonic.net/bristlecone/intro.html - The Bristlecone Pine and dendrochronology information
more shortly
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