Global climate change triggered by global warming: Part 2

This article is the second installment of our presentation of a position paper issued by the Center for Inquiry's new Office of Public Policy in Washington, D. C. The first installment appeared in our previous issue. The author is Stuart D. Jordan, a senior staff scientist (emeritus) with the NASA Goddard Space Flight Center. The entire text is available on the CFI/Washington, D.C. Web site at www.cfidc.org/opp/jordan.html.--Kendrick Frazier, Editor

Since the case for natural forcing of the current rapid global temperature rise is weak, we must ask what human activities are likely to be major causes. Here a near consensus has arisen among most climatologists that human-rated greenhouse gases are the main culprit. While the scientific arguments supporting this position are now known to most knowledgeable people, it is useful to repeat them here in the interest of presenting a complete contemporary picture of global warming and climate change.

The Greenhouse Effect

There is complete agreement among research scientists whose work appears in the refereed literature that the "greenhouse effect" is a real physical process that is contributing to global warming. The greenhouse effect occurs because the sun's relatively short-wavelength radiation from the hot solar surface passes through Earth's atmosphere and reaches ground level to be absorbed by Earth, where the surface temperature is much lower than the sun's. Much of the longer-wavelength infrared radiation emitted by the cooler Earth is absorbed by Earth's atmosphere. Thus, a part of the sun's radiant energy is trapped by Earth's atmosphere. If the amount of incoming solar radiation that is absorbed and trapped exceeds the amount that is reflected and re-radiated into space, there is an imbalance, and Earth's temperature will begin to rise. The excess amount will warm the atmosphere until a higher equilibrium temperature is reached, at which the total rate of energy loss from Earth to space equals the amount that is retained by Earth.

Indeed, thanks to the greenhouse effect, our atmosphere has had equilibrium temperatures (within a limited range, determined by many different processes) sufficient to sustain, ultimately, human life. If Earth had no atmosphere, the mean global surface temperature would be approximately fifty degrees centigrade colder!

The problem of the current global warming occurs because of the aforementioned net imbalance in Earth's energy budget, with more solar energy being retained than is radiated back into space. This is due to the increase in greenhouse gases produced by human activity since the beginning of the Industrial Revolution, a process that continues today with an ever-increasing atmospheric concentration of the culprit gases (Prentice et al. 2001; Sarmiento and Gruber 2002). This situation makes global warming and some associated climate changes inevitable.

The Dominant Role of Carbon Dioxide Today

Greenhouse gases produce this imbalance when their concentration in the atmosphere is increased. The role of the most-offending greenhouse gas, carbon dioxide, will illustrate the process. Because carbon dioxide gas is a major by-product of burning the fossil fuels that power much of our industry and transportation, its production and release into the atmosphere continue to increase today. Carbon dioxide is an efficient absorber of the infrared radiation emitted by Earth, and increasing its concentration in our atmosphere increases the rate at which Earth's infrared radiation is trapped. Moreover, by warming the atmosphere above the previous equilibrium temperature, more water vapor is produced, which is the most effective greenhouse gas of all (Soden et al. 2005). The warming associated with these processes is further amplified by deforestation, which reduces the capacity of the land to absorb atmospheric carbon dioxide. Since the land is the only other major natural sink for this greenhouse gas, along with the oceans, deforestation contributes significantly to global warming (Sarmiento and Wofsy 1999).

Other warming processes are set in motion by those stimulated by an increased concentration of atmospheric carbon dioxide. Some of these could produce "runaway" phenomena until they go to completion. In the first part of this article, we cited the effect of reducing the bright reflecting ice cover in the Arctic, leading to greater absorption of solar radiation by the less reflecting water surface, thus inducing still more melting. In this case, the process could continue until the Arctic Ocean is entirely ice-free. Methane is an even more efficient greenhouse gas than carbon dioxide. Melting of the permafrost at high latitudes could release large quantities of methane into the atmosphere, and Arctic regions are warming most rapidly of all. While the consequences of methane release are still being debated in the scientific literature, this and other processes triggered by continued global warming are now under investigation, as their cumulative effect could be extremely harmful (Prather et al. 2001).