Abstract
Introduction During the late 1980s and 1990s, the alleged "Greenhouse Effect" captured the interest of news magazines, radio, and television programs. Predictions from various scientists range from a coming cataclysmic, worldwide impact to little or no impact at all. However, those scientists on the apocalyptic side seem to have captured the greatest interest from the media as well as policy makers from state governments and international organizations, such as the World Bank. Foreboding scenarios are conjured, including world food shortages, melting polar ice caps accompanied by severe flooding of coastal land masses, destruction of ecosystems, and greatly increased severity of storm activity (hurricanes, etc.). Most of the greenhouse effect is attributed to the burning of fossil fuels which releases tremendous amounts of carbon dioxide and other gases into the atmosphere, trapping heat and warming the planet.[1]Because of the many ominous predictions for the climate, policy makers from both national governments and international organizations are demanding policy adoptions in the form of carbon taxes, mandated efficiency measures, and subsidies for non-carbon dioxide-emitting technologies to roll back greenhouse gas emissions to their 1990 levels.[2] While there is disagreement among climatologists regarding the significance of the "greenhouse" effect, there seems to be more agreement among other investigators that "cutting back" significantly on greenhouse gas emissions would have more serious negative worldwide impacts, with large Gross Domestic Product reductions, resulting in lower living standards in the long run.[3] Looking back to the recent past, it is now all but forgotten that some outspoken climatologists in the late 1970s predicted a completely opposite scenario, a return to an ice age with cataclysmic impacts, which also demanded immediate attention. The Use of Climate Models To measure historical as well as future impacts of carbon dioxide emissions on climate variables, scientists have developed mathematical climate models, whose features are discussed in a recent book by Robert Balling.[4] He points out that many of these climate models predict substantial increases in global temperature for increases in carbon dioxide levels, and it is these predictions that have attracted the attention of policy makers and the media.[5] For example, a doubling of carbon dioxide levels results in an increase in global temperatures in eight climate models mentioned by Balling.[6] Based on these models, global average temperature increases from a low of 1.9 to a high of 4.8 degrees centigrade. What is generally not appreciated is that the models also unanimously predict increases in precipitation as well as increases in temperature, and these levels range from 3 to 15 percent.[7]What is also usually neglected in the popular press is that the climate models have significant limitations on the simulation of the ocean-atmosphere interaction, which is not yet well understood. Balling says, "Until we have better knowledge of the coupling between oceans and the atmosphere, the model predictions must be treated with considerable caution."[8] Another very significant difference among the models is their cloud-climate responses. The Historical Temperature Record and Future Implications In Figure 1, we show global average temperature anomalies for the period 1881 to 1990.[9] If we fit a linear trend line through the data, we find that global average temperature has increased by .56 degrees centigrade. However, over this same period, equivalent carbon dioxide levels have increased by about 40 percent. Assuming that there is a relationship between carbon dioxide levels and temperature change, this would imply an increase in temperature of about 1.4 degrees for a doubling of carbon dioxide levels, which is below the temperature range predicted by the climate models reported by Balling.However, it often can be misleading to fit a linear trend line through historical data and draw firm conclusions from it. Referring to Figure 1 again, we have fit two additional trend lines through the historical temperature data—a quadratic and a cubic trend. Using these three trend equations, we have extrapolated temperature anomalies from 1991 to 2050, and we observe a wide range of temperature difference, depending upon which historical trend is used. Thus, historical data may not determine a unique trend and can be highly misleading in predicting future temperature changes.