The Science of Global Climate Change

Global Warming

The Intergovernmental Panel for Climate Change estimates that the earth has warmed from 0.4 to 0.8 degrees Celsius over the past century. Comparing surface land readings to surface temperatures the IPCC points out that "recent warming has been greater over land compared to oceans; the increase in sea surface temperature over the period 1950 to 1993 is about half that of the mean land-surface air temperature." However, the IPCC also notes that sea levels have already risen 0.1 to 0.2 meters in the past century and are expected to rise between 0.09 to 0.88 meters in the next century due to expanding warmer waters and the melting of continental glaciers and ice sheets. Based on this current data, NASA’s Goddard Institute for Space Studies estimates that the earth could see global surface temperature increases from 0.5 degrees C to 1.0 degrees C over the next 50 years. The IPCC takes a stronger approach with estimates of 1.4 degrees C to 5.8 degrees C temperature rise over the next century.

Satellite Ambiguity

Dr. S. Fred Singer has argued against such statistics in the past, demonstrating that the Microwave Sounding Unit (MSU) satellite data and weather balloons had not shown a distinctive warming trend in atmospheric temperatures. However, MSU data did show a trend starting with the 1998 El Nino event, but many scientists consider this single climatic event a null point in a total trend. The main rebuttal given by the IPCC is that the approximate twenty years of measurements (starting in 1979) are not enough to compare adequately with the longer surface data and that by combining data from weather balloons, available since the 1950s, the data from the lowest 8 km and the surface data are more comparable at 0.1 degrees C per decade. Other possible reasons given include the cooling effect of aerosols through ozone depletion and other volcanic and weather phenomenon such as the Mt. Pinatubo eruption in 1991.

Natural Causes vs. Anthropogenic Causes

Such natural events as the Mt. Pinatubo eruption can demonstrate the effects of non-anthropogenic influences on climate. As the National Research Council explains, "the injection of large quantities of sulfur dioxide, which changes to sulfuric acid droplets, and fine particulate material into the stratosphere (the region between 10 and 30 miles altitude where the temperature rises with increasing altitude) by major volcanic eruptions like that of Mt. Pinatubo in 1991 can cause intervals of cooler than average global temperatures." But this also means that warming can have its natural causes as well. The ice core samples taken from Greenland and Antarctica as well as other evidence can give us a glimpse of the last 400,000 years on earth. This evidence has shown temperature variability among local and regional spaces to increase by over several degrees C "periods as short as a decade."

Anthropogenic (Man-made) Change

The earth is warmed by the "greenhouse effect." Greenhouse gases include carbon dioxide, nitrous oxide, water vapor, and chloroflurocarbons. These gases "trap" a certain amount of heat when the sun’s rays bounce off the earth’s surface. NASA states that if we did not have any greenhouse gases or clouds, the earth’s average surface temperature would be -18 degrees C! All greenhouse gases, minus industrially-produced gases such as hydrofluorocarbons, occur both naturally and as a result of human activities. But the added human pressure can take its toll: NASA quotes the IPCC stating that "since the industrial revolution, carbon dioxide levels have increased 31 percent and methane levels have increased 151 percent. Paleoclimate readings taken from ice cores and fossil records show that these gases, two of the most abundant greenhouse gases, are at their highest levels in the past 420,000 years." And "in the Earth’s distant past, drastic increases in carbon dioxide nearly always coincide with large increases in Earth surface temperatures. Conversely, ice ages are almost always accompanied by a decrease in carbon dioxide." The IPCC has also observed that in the year 1800 the concentration of carbon dioxide in the atmosphere was 280 parts per million compared with 367 ppm in 1999.

Naturally, carbon dioxide is involved in a global cycle of terrestrial and oceanic "sinks" that store carbon. Plants store a certain amount of carbon dioxide and terrestrial uptake is dependent upon "the balance of net primary production and carbon losses due to heterotrophic respiration and fire" -- essentially, the rate at which plants uses carbon dioxide to grow and the rate at which burning such biomass releases carbon back into the system. The ocean is also an important factor in the storage of carbon dioxide: the IPCC explains that oceanic uptake is the main reason why atmospheric carbon dioxide is increasing at only half of the rate of fossil fuel emissions. Yet the process is slow and limited, taking almost a hundred years; the ocean will increasingly become saturated with carbon dioxide.

The following set of graphs and the explanation by the IPCC compare both anthropogenic and non-anthropogenic causes of global warming. The end comparison favors a combination of both.

The Water Vapor Question

Water vapor is also considered a greenhouse gas: in fact, it absorbs even more heat than carbon dioxide. In addition, water vapor is more prevalent than other trace greenhouse gases. The National Safety Council’s Environmental Health Center states that "water vapor is responsible for about two-thirds of the natural greenhouse effect." However, water vapor does not stick in the atmosphere as long as other greenhouse gases as it quickly passed through the hydrological cycle leaving the atmosphere within a few days. While human activities might not directly increase the amount of water vapor in the atmosphere, the IPCC is concerned about the water vapor feedback which could be exacerbated as the earth warms and more water is evaporated into the atmosphere.