Global warming has become a modern issue of considerable significance. It has been the subject of many debates, articles and conferences. Despite the amount of debate around the issue, there is still no clear conclusion. Yet the possible consequences that are attributed to the threat are highly concerning. As one report describes:
The most recent projections of state-of-the-art computer models of the Earth's climate (GCMs) have projected a globally averaged warming ranging from almost 3 to 10.7 degrees F. over the next 100 years, if greenhouse gases continue to accumulate in the atmosphere at the current rate. Climate scientists believe that such a warming could shift temperature zones, rainfall patterns, and agricultural belts and, under certain scenarios, and cause sea level to rise. They further predict that global warming could have far-reaching effects -- some positive, some negative depending how it may be experienced in a given region -- on natural resources; ecosystems; food and fiber production; energy supply, use, and distribution; transportation; land use; water supply and control; and human health" (Justus & Fletcher 2002, p. 2)
The seriousness of the potential consequences may explain why the issue continues to be debated so widely. If these consequences are realistic, then everything should be done to understand the issue and prevent the worst case scenario from becoming the reality. This also explains why so many resources have been applied to global warming. This includes research funds and funding to support government and environmental actions.
Yet the reality is, that there is still no clear answer as to whether global warming is a real threat, or an imagined one. The possible consequences and the funds currently being applied to the issue are two good reasons why the issue deserves significant consideration.
National Oceanic and Atmospheric Administration's (NOAA) researchers reported that the 12 warmest years (globally averaged) since historical records have been kept occurred in the past two decades, with 1990 and 1998 among the warmest" (Justus & Fletcher 2002, p. 4).
Ever since accurate temperature records have been kept, the 1980s have been the warmest 10-year period recorded and included several warm years" (Mahahan 1994, p. 409)
The global-mean temperature at the earth's surface is estimated to have risen by 0.25 to 0.4 "C during the past 20 years" (CGER 2000, p. 1).
The Antarctic is experiencing significant ice breakups (Revkin 2002).
The 150-year period from 1846 to 1995 showed a trend with rivers and lakes being covered with ice for reduced lengths of time (Magnuson et al. 2002).
Converting the figures of ice coverage to temperature indicates a warming of 1.8 degrees Celsius (Magnuson et al. 2002).
The disparity between surface and upper air trends in no way invalidates the conclusion that surface temperature has been rising" (CGER 2000, p. 2).
A the warming trend in global-mean surface temperature observations during the past 20 years is undoubtedly real and is substantially greater than the average rate of warming during the twentieth century" (CGER 2000, p. 2).
Milankovitch's theory of climatic change can explain the seasonal variation, based on the natural variation of the solar energy received by the Earth (Kaufman 2002).
Milankovitch used his theory of climatic change to predict temperates going back 600,000 years (Kaufman 2002).
A study on deep-sea sediments determined the temperatures going back 450,000 years and confirmed the accuracy of Milankovitch's predictions (Naish et al. 2001).
Ocean circulation systems also explain the current rise in temperature, since they multiply temperature changes (Sternlof 2002).
The Gulf Stream is currently operating at about two-thirds of its rate during the last ice age (Sternlof 2002).
Some authorities argues that recent warming trends are largely artifacts of the location of temperature measuring facilities in urban areas subject to localized anthropologized heating" (Manahan 1994, p. 409).
Satellite measurements taken since the 1970's have "shown annual fluctuations but not overall trends" (Manahan 1994, p. 409).
Evidence of natural variability of climate is large enough that even the record-setting warmth at the end of the 20th century does not allow a vast majority of knowledgeable scientists to state beyond a reasonable doubt that weather extremes experienced over the past two decades are attributable to 'global warming,' at least at the present time" (Justus & Fletcher, 2002, p. 5).
One of the main pieces of evidence global warming is based on is a rise in surface temperature over the last twenty years. The evidence for global warming according to Justus and Fletcher is based on the temperatures from 1980 to 2000, with 12 of these years being the warmest years 'since historical records have been kept.' While this may initially seem like significant evidence, closer analysis shows one major problem. The phrase 'since historical records have been kept' suggests that these twenty years are being compared to a long length of time. However, in reality, these temperature records only refer to around a century of data. The other evidence on changing temperature is based on the same thing, a rise in temperature since 1980. A temperature rise over this time-frame is not being compared to thousands of years of data, but to a century of data. This makes it possible that this rise is either a random event or an event that occurs periodically. In short, with the amount of time this twenty year period is being compared to, it is not reasonable to suggest that it is an unusual event.
This rise in temperature is also attributed to the impact of man. While this twenty year time-frame does coincide with the impact of man, including such things as the use of aerosol sprays and the chemicals produced by manufacturing and vehicle exhausts, this is not significant enough to say that it is the cause of the temperature increase. A rise of temperature over a twenty year period could be attributed to a number of factors. For example, plotting the population of the world and the temperature would show the same upward trend. Plotting the number of women employed and the temperature would also show the same trend. This illustrates that just because two factors both increase over a period of time does not mean they are related. Therefore, issues like deforestation and an increase in chemicals in the atmosphere are not necessarily the cause of an increase in temperature.
The rise in temperature is also related to temperature-dependant effects. For example, the article by Revkin suggests that global warming is responsible for the Antarctic ice breakups. The reality is that the rise in temperature can be said to be responsible for the breakups, but this rise in temperature is not necessarily a product of global warming.
The evidence then can be agreed with, with it accepted that the temperature has increased in recent years. However, the reason for this increase is not known. It could be a product of man's impact on the earth, or it could be due to many other factors.
This leads to the consideration of one major argument given by those opposing global warming. This argument is that changing temperatures are an environmental reality and are not necessarily a product of man's impact. Milankovitch's theory explains this ongoing climatic change by relating it to the natural variation in the solar energy the earth receives. Much like how supporters of global warming predict future climatic conditions, Milankovitch predicted past climatic conditions. The major difference is that Milankovitch's past predictions can be tested to verify their accuracy, while future predictions cannot. The study by Naish et al. confirmed the accuracy of Milankovitch's predictions, giving some credibility to the possibility that the environmental changes are part of a natural process.
Yet, the accuracy of Milankovitch's predictions is not enough to say that the change in temperature is a natural process. Milankovitch's predictions may work in the past but this is not evidence to suggest that they will work in the future. It is entirely possible that Milankovitch's predictions only work in a system defined by natural causes. Perhaps, the introduction of man has changed that balance so that while the predictions work in the past, the impact of man means that they will not apply to the future. It is also important to recognize that just because future projections made by supporters of global warming cannot be verified, does not mean they are not correct. The fact remains that there is no way to verify future long-range predictions. This means that Milankovitch's contentions that the changes are based on solar energy cannot be proven and global warming supporters can also not prove that man is the cause.
Another of the views expressed by the con side is that ocean circulation systems account for the current rise in temperature. These ocean circulation systems combine with increased temperature and multiply the effect of temperature change. However, while this can explain why the polar ice caps are melting, it does not explain the source of the temperature change.