In his attempt to give scientific justification to the global warming scare (Basic science explains why we must cut our emissions
, January 24), Mark Swanepoel ignores the fundamental scientific reasons why rising carbon dioxide (CO² ) is not causing, and cannot cause, dangerous climate change.
The Earth cools itself mainly by emitting infrared radiation into space. Greenhouse gases reduce this cooling.
CO² , a weak greenhouse gas, has only one significant absorption band for this infrared, at 15 micron. But the band is already saturated. All of the 15 micron radiation leaving the Earth’s surface is already absorbed. So adding more CO² has a small and diminishing effect (lowering the height of absorption and slightly increasing it in the shoulders of the band).
Standard radiation heat transfer shows that the direct effect of doubling the amount of CO² in the air from present levels (390 parts per million, or ppm) would increase the global temperature about 1°C.
However, there would be feedback (response to change) and it would be negative (countering the change), and so the actual temperature increase would be much less than 1°C.
All observation and records confirms this, and this is consistent with satellite measurements.
A likely agent for negative feedback is low clouds. Heating increases evaporation, leading to more water vapour in the air, which condenses into clouds. The cooling effect of the clouds, which reflect away sunlight, outweighs the heating effect of extra water vapour.
Over hundreds of millions of years, CO² has fluctuated from above 6000ppm to the present extreme low level of below 400ppm, and has not had a noticeable effect on temperatures. 2 was even lower than now, global temperatures, in the southern and northern hemispheres, were rather higher than now. CO2 increased considerably from 1940 to 1970 but global temperatures decreased. Since 1998, CO2 has continued to increase but there has been no increase in global temperatures.
There is no evidence to suggest that the slight warming over the last 150 years is anything but natural, just like previous natural warming periods.
There has been no increase in extreme weather events.
For example, the recent floods in eastern Australia were less severe than those in 1974 and much less severe than those in the 19th century. Rising CO² will have no significant effect on our climate. But it will make our crops and forests grow much better.
MARK SWANEPOEL: Climate change
Basic science explains why we must cut our emissions
SOUTH African business leaders must understand global warming well enough to make decisions to safeguard our future. In several articles published on these pages, one of your correspondents on global warming has exhibited ignorance about the subject. He has also written on the relative benefits of nuclear power stations and wind farms, without having considered where parts will be manufactured, by whom, and the total net life-cycle costs to the country, including economic multipliers. Similarly, an astronomer at the Boyden Observatory misled the public on the basis of a book that drew a wrong conclusion from limited data.
The Intergovernmental Panel on Climate Change bases its conclusions on the work of experts in solar, atmospheric and oceanic physics. Yes, climatologists make mistakes — but no denialist has disproved the greenhouse effect: this would necessitate a scientific revolution. Below, I explain the basic science. Hopefully, as the frequency and effect of climatic disasters increase, denialists will actually read and understand it.
The "biosphere" is the zone of the earth’s atmosphere, oceans and crust that contains life. The survival of many species depends on climatic stability. Weather phenomena are ultimately driven by the energy entering and leaving the biosphere. The significant sources of energy entering the biosphere are the sun, geothermal energy, tidal energy, and manmade power sources. Almost all energy leaving the biosphere does so as reflected, diffracted and refracted visible light, and radiated heat (infrared photons). The energy entering and leaving the biosphere exhibits random and cyclic fluctuations superimposed on a long-term trend. If more energy enters the biosphere than leaves it, its average temperature rises, and vice versa.
Temperature is a measure of the energy in the movement of atoms and molecules about their own centres, which we sense as heat. Within air, heat is transferred by conduction, in which atoms and molecules jostle each other, and by radiation, in which infrared photons are emitted and absorbed by atoms and molecules. Atmospheric molecules are separated by gaps that are vast on an atomic scale. Few air molecules collide in a given time compared with those in solid materials, so the atmosphere conducts heat poorly. Infrared photons bypass the nitrogen, oxygen and argon that make up almost all the atmosphere, to be absorbed by a greenhouse gas or escape into space.
Space is a vacuum, so heat cannot be conducted from the earth: it must be radiated away as infrared photons. Infrared photons are low-energy light that humans cannot see. As the scale of the electromagnetic disturbance that produces a photon decreases, the photon’s wavelength becomes shorter and its energy increases. Most energy in sunlight is carried by photons of visible light. Photons of different wavelengths do not pass through the same material with equal ease, because they have different propensities to be diffracted and absorbed by the electron clouds of the material’s atoms or molecules. A material can be transparent to photons within a limited band of wavelengths. Only fractions of all incident photons are absorbed and diffracted within a certain distance in a gas. One can shine a beam of photons of a certain wavelength through a column of gas and measure the fractions of incident photons absorbed, diffracted sideways and transmitted. If one repeats this for many different wavelengths, one can plot graphs of the gas’s spectral transmission, absorption, and diffraction.
Visible sunlight is not absorbed by the natural atmospheric gases. Due to the ratio between the wavelengths of blue photons and the diameters of nitrogen and oxygen molecules, such photons are greatly diffracted in the sky — so it appears blue. Green photons undergo moderate diffraction through the depth of the atmosphere, yellow photons are somewhat diffracted, orange photons still less, and red photons are little diffracted. Infrared photons of longer wavelengths are negligibly diffracted. (However, at dawn and sunset, the sun’s photons travel much further through the atmosphere to reach us, so even its orange and red photons are significantly diffracted.) Clouds are white because water droplets refract and mix photons of all visible wavelengths.
Thus photons of sunlight either reach the earth’s surface, or are refracted and diffracted back into space. Much sunshine that reaches the surface is reflected, and much of this returns to space. The energy of photons that are not lost to space ultimately ends up in the tiny movements of atoms and molecules that we sense as heat. An infrared photon travelling through the atmosphere may encounter a greenhouse gas molecule that absorbs it. The more such molecules there are per unit volume, the greater the chance of absorption . Some greenhouse gases absorb infrared photons of more wavelengths than others. The energy of an absorbed photon may eventually be re-emitted as another photon, or transferred to other atmospheric molecules through conduction. Thus the energy that would otherwise have been radiated into space is retained as heat. The types and quantities of greenhouse gases in the atmosphere determine overall heat retention.
What of water? The speeds of molecules in liquids and gases follow skewed, long-tailed Maxwell distributions. As a liquid becomes hotter, the peak occurs at a greater speed and the long, fast tail lengthens. Molecules of a liquid are attracted to each other, and the lopsided nature of these forces at the surface creates surface tension. Only some of the molecules in a liquid move quickly enough to evaporate into the gas above. Due to the long- tailed speed distribution, the number of molecules sufficiently energetic to leave a liquid increases exponentially with temperature — this is apparent on humidity charts.
Water vapour is itself a greenhouse gas. If humid air cools sufficiently, the vapour condenses. Clouds, snow and ice refract and reflect more photons away from the Earth, so eventually thermal equilibrium should be re- established in a biosphere that will generally be hotter and wetter, but with some areas cooling due to greater cloud cover, and/or suffering harsher winters. This is climate change. What matters is not the change itself but the rate of change. Many species will be unable to adapt quickly enough.
Weather is driven by differences in air temperature across the earth, and vertically. Rapid heat transfer would limit temperature differences and weather phenomena, but air conducts heat poorly. Large volumes of air adopt the temperature of the terrain under them. Hot air rises while cold air sinks, driving winds. Thus the root of weather is large- scale convection caused by poor heat conduction. Greater humidity in a warmer world will magnify temperature differences between air masses, because of the opposing effects of water vapour and condensed water droplets on energy retention. This will magnify the frequency and intensity of weather phenomena.
Global warming is attested to by the temperatures recorded by meteorological stations worldwide, by satellite measurements of the solar output and radiation emanating from Earth, and by satellite measurements of sea level (the current rise being mostly due to thermal expansion of water). Changes in species distribution and behaviour, and increasing thawing of permafrost are in agreement. The biosphere is heating up, yet we are making it increasingly difficult for heat to escape. It is difficult to control natural greenhouse gas emissions, but we can and must reduce man-made emissions.
- Dr Swanepoel is a research physicist.