Tens of thousands of years ago, ice covered much of the land we now inhabit. Wholly natural causes warmed the earth, melted the ice, allowed plants and animals to thrive where once they were excluded. Within our recorded history, we have had periods significantly warmer (Medieval Warm Period, 900-1300 A.D.) and periods significantly colder (Little Ice Age, 1300-1500) than the modern era, none of these changes being attributable to human activity. Some climate researchers believe that there is a 1500-year climate warming / cooling pattern due to the overlapping of several solar cycles of shorter periods. Recently, the prevailing “scientific consensus” has been that humans have been contributing somewhat to a general global warming by their emissions of carbon dioxide, primarily due to industrial and agricultural development. United Nations’ scientific panels have concluded that if we do not drastically reduce such industrial activity and emissions, the atmosphere will become dangerously warm; the polar ice caps will melt; the seas will rise; widespread destruction will ensue. A set of agreements reached in Kyoto (1997) called for emissions control limits subsequently found to be impractical, with some of the more egregiously emitting nations exempted for economic and political reasons.
In the past few years, ardor for control of “greenhouse gases,” principally carbon dioxide and methane, has cooled, at least among the public, as reflected in public opinion polls. Some notable scientists have called the global warming modeling and warnings into question, as well. This September, the 1973 Nobel Laureate physicist Ivar Giaever resigned as a Fellow of the American Physical Society in protest against the Society’s, to him dogmatic, position that the evidence for global warming is so strong that it is “incontrovertible” that global warming due to these emissions is occurring and that therefore we “must reduce emissions of these greenhouse gases starting now.” In his resignation letter, Dr. Giaever noted that the claimed change in the average temperture of the earth (a tricky measurement indeed) was less than two degrees Farenheit over the last 150 years, while human well-being has clearly improved.
This year a dissenting panel of scientists, including some eminent atmosphere and climate specialists, issued the report “Climate Change Reconsidered,” casting doubt on the accuracy of the predictions of dire consequences in the absence of stringent carbon dioxide emissions controls. The data on which the predictions had been based are spotty. Temperature measurements are missing over much of the globe. Those made on land can be corrupted by local effects. Despite their sophisticalion, the models used in predicting climate change cannot capture many crucial phenomena, including the influence and variability of clouds. The report concluded that we do not have the kind of information yet on which to base sweeping economic and political changes to limit further industrialization.
Why is it so hard to predict the impact of “greenhouse gases” on climate? In short, because there are so many potentially important factors still inadequately understood. A simple model of the Earth-Sun system would be a rotating, dry planet, lacking an atmosphere, heated by the Sun, reflecting some of that energy, but radiating more and more of it as the planet gets warmer, until the outgoing reflected and radiated energy match, on average, the incoming energy. The mean global temperature of this model Earth would still vary, as the Earth’s position with respect to the Sun varies and as the output of the Sun itself varies. If we were to add an atmosphere of just oxygen and nitrogen, the energy balance would be much the same, and the temperature of the atmosphere near the surface would match that of the surface. Adding “greenhouse gases” in significant amounts negligibly changes the energy received at the surface of the Earth from the Sun, but they would absorb some of the energy radiated by the warmed surface, due to the longer wavelengths of this primarily infrared radiation, some of which wavelengths are absorbed preferentially by the “greenhouse gases.” Compared to the situation without the “greenhouse gases,“ the Earth’s surface will be somewhat higher, thus the air temperture will be somewhat higher due to this blanketing effect, the partial absorption of the outgoing radiation. This is the “greenhouse effect.”
Most of the Earth’s surface is covered with water, primarily the oceans. As the wet (or merely moist, as for land) surfaces heat up, water evaporates, rises thorugh the atmosphere, cools, condenses, forms clouds, and precipitates as rain, hail, snow. This is where modeling becomes more difficult. Clouds reflect some of the sunlight, lessening the energy reaching the Earth. If the Earth were wholly covered by clouds, as in the “Nuclear Winter” scenarios associated with nuclear war, the temperature of the Earth’s surface and of the air would fall drastically, leading to widespread plant and animal extinction. If the clouds were primarily dust, as in the Nuclear Winter scenario, they would dissipate in time due to precipitation and settling (“fallout“). If the clouds were primarily water, they would produce rain and snow, etc., and become diminished in total weight, in thickness, in extent. As the clouds diminished, their cooling effect would diminish and the Earth would heat up, leading to more evaporation and the replenishment of the clouds, eventually restoring the former temperature equilibrium..
This tendency of clouds to correct over-heating or over-cooling is “negative feedback,” an important feature of the atmosphere as yet to be successfully modeled. The impacts on cloud formation due to cosmic rays, micrometeors, volcanoes, sea spray salt, and other open sources like deserts and quarries and unpaved roads, etc., complicate the physical situation greatly and make modeling extremely difficult. As Science News of December 4, 2010, noted, there is little known about “how tiny particles called aerosols influence climate.” A retired expert in aerosol science myself, I believe that these airborne particles are likely to be quite important and yet difficult to model correctly.
Often the modelers must introduce adjustable parameters, “fudge factors,” in laymen’s terms, to “account” for all that cannot be carefully described. The models are “tuned” by comparing with past data and adjusting these factors. As we are warned with respect to investing, “the past is no guarantee of the future.” A model that fails to match the past is certainly suspect, but even one that is tuned successfully to match the past may not be reliable for prediction.
The past ten years have shown no unambiguous global warming. Since there are myriad possible measurements, by “cherry picking” the data the “warmists” can make the case for warming and the “deniers” can make the opposite case. Currently, the carbon dioxide concentration in the atmosphere is nearly 400 ppm. The 2 to 4 ppm per year of the carbon dioxide added to the atmosphere that is attributed to human activity (is “anthropogenic”) is unlikely to become a problem in the next few decades. Doubling the CO2 level in the atmosphere is predicted to increase mean global temperature by roughly two degrees Farenheit. Doubling the carbon dioxide level would require roughly a hundred-fold increase in mankind’s “contribution,” not impossible, but unlikely, especially as energy technology continues to improve. The impact would be warmer nights, with relatively unchanged days, the modelers predict. Plants should grow more rapidly. A somewhat greater fraction of the Earth’s surface will become temperate, suitable for plants and animals, the biosphere. Recently, sea levels have been rising at a rate close to 1 foot per century, certainly manageable. Granted, any changes produce winners and losers. There are reasons to believe that the scariest consequences will not result, but there are too many issues to analyze them all here.
We will likely not see calamitous results from “global warming” in the next few decades. Meanwhile, we will learn to adapt to those changes that do result. Unfortunately, there is no way to prove this, so the debates between “alarmists” and “deniers” can be expected to continue. As more is known about the impacts of man and nature on our climate, one can hope that the temperature of these debate will lessen.
Douglas Winslow Cooper, Ph.D., is a freelance writer and retired physicist, author of Ting and I: A Memoir of Love, Courage, and Devotion, available from Outskirts Press and amazon.com. His email address is firstname.lastname@example.org .