- Shopping Bag ( 0 items )
* * *
If an asteroid hurtling toward Earth would, with strong probability, strike this planet in forty years, raise sea levels permanently between six inches to sixteen feet, force up to one-quarter of all species into extinction, inaugurate plagues and disease, inundate parts of some nations, drown populated islands whole, render coasts uninhabitable, intensify hurricanes, typhoons, and tornadoes into record-breaking storms, cause frequent floods and landslides, and kill millions of people, then every government would work furiously to discover how that asteroid might be diverted or destroyed.
There is no such asteroid (as far as we know), and there is no international cooperation, therefore, to stop it. But all the rest in this scenario is very possibly true. It is just happening more slowly (and at this very moment) than the future impact of an asteroid. The cause is not one impending catastrophic event. It is our own burning of carbon. Ironically, solutions to the problems caused by burning carbon, though difficult to achieve, may, in fact, prove easier to discover than solutions for the impact of an asteroid.
Climate is not "weather" in the usual sense, or even global weather over long periods of time. Large, multiple earth systems, physical, chemical, and biological, produce world climate. These involve the atmosphere, land, oceans, and living organisms. For the first time ever, human activity is now measurably changing global climate.
Increased levels of greenhouse gases, especially carbon dioxide (C[O.sub.2]), act as the chief vehicle for human impact on Earth's climate systems. (See Chapter 13, below.) The main source of these increased levels is human combustion of fossil fuels. Burning wood, forest fires, and slash-and-burn techniques to clear land contribute, too. For a thousand years prior to 1800, the atmospheric C[O.sub.2] level measured about 270 parts per million (ppm). In the past two centuries, this has risen sharply, at an increasing rate, to 370 ppm, as high as it has been for 420,000 years. Even if we stopped using fossil fuels today, these concentrations would remain for decades. Given increasing global energy use per capita and further population growth, greenhouse gas levels will rise more. No one knows when, if, or at what level they might stabilize.
Greenhouse gases trap heat. As C[O.sub.2] levels rise, the atmosphere also holds more moisture and energy. C[O.sub.2] is absorbed mostly by oceans and some by forests (these are called C[O.sub.2] "sinks"), but these sinks cannot absorb atmospheric C[O.sub.2] as fast as human activity now produces it. Many countries neither regulate nor regard it as an air pollutant. The Kyoto Protocol of 1998 is designed to reduce C[O.sub.2] emissions worldwide, but the Protocol has proved divisive. In late 2004 Russia ratified it. This triggered its observance by fifty-five signatory countries, which also happened to produce 55 percent of the world's C[O.sub.2] emissions. But the United States, China, and India, the three most populous countries, rejected the Kyoto Protocol.
Climate change also involves the interplay of ocean temperatures, currents, chemistry, and salinity. Changes in both surface and deep ocean currents occur. Marine life including plankton and archaea are affected and set off further changes. Glacial ice everywhere is melting; a huge amount of melt occurs in Greenland. The resulting cold water runoff might disrupt ocean currents and prevent warm water from reaching northern and western Europe. From 1953 to 2003 the Arctic ice pack lost about half its thickness. Because the size of the pack has diminished, too, less heat is reflected back by white ice and more is absorbed by darker water, further reducing the ice, a positive feedback loop. Atmospheric moisture and winds are among the changing earth systems, as is the solar heat reflected by increased cloud cover and decreased ice and snow cover. Changes in forest density and location play pivotal roles. Because so many factors interact, atmospheric science, forestry, oceanography, ecology, microbiology, and meteorology are all involved.
To record changes in earth systems and in global climate is a daunting task. To predict changes into the future requires discovering what global climate was in the distant past and why it changed. Tree rings, fossils, and ice cores from glaciers and the seabed provide data. As we understand how earth systems interact and produce global climate, we model them mathematically and approximate their actual performance. However, even great computing power, like that of the National Center for Atmospheric Research in Boulder, Colorado, gives varied predictions. Why? Some data cannot be known with precision and the mathematical models themselves differ. The single most unpredictable variable in calculating and predicting climate is how much carbon humans will burn in the next decades.
Average global temperature rose by almost 1°F in the past century, but warming varied by location. Areas of Alaska and Canada increased 4° to 7°F. As C[O.sub.2] concentration accelerated, the World Meteorological Organization noted that the average global temperature rose three times faster from 1975 to 2000 than from 1900 to 1975. In Europe, the summer of 2003 was the hottest in 500 years. Authorities attributed 26,000 deaths to the heat. Globally, nine of the ten warmest years recorded between 1861 and 2000 occurred in the 1990s. Estimates of temperature increase in the present century range from 1.4 to 5.8°C (2.5 to 10.4°F).
In the past fifty years tropical storms have lasted 60 percent longer and have produced winds 50 percent stronger than known historical averages. Since 1970, category 4 and 5 hurricanes and typhoons have increased. During 1987-2004 they were 57 percent more common than during 1970-1981. These and similar statistics do not prove that global warming is the sole cause, but they create concern. Unabated, such changes will lead to climate shock and catastrophic consequences. A few models indicate the possibility of sudden reversal to a much colder climate in the Northern Hemisphere and in Europe in particular, especially if global warming shuts down ocean current (thermohaline) circulation that moves warm water from near the equator toward the poles.
Future climate change now appears to be more severe than estimated as recently as 2001. Sea levels are rising. (They rose four to eight inches in the past century.) This occurs several ways. First, seawater expands in volume as it warms (thermal expansion). Floating ice already displaces water, but ice not floating can melt, too. This is of huge concern if the vast ice sheets of Antarctica and Greenland melt. Ice not floating in the sea can also break off and, like ice cubes dropped in a drink, raise the sea level. For the next hundred years, estimates of increase in sea level elevation range from four inches to sixteen feet. Coastal wetlands will be impacted. Mountain glaciers are receding. By 2070 Glacier National Park in Montana may have no glaciers. All coastal cities will be affected, some perhaps severely. Some shorelines will disappear. Regions of poor countries such as Bangladesh, inundated with coastal floods, may cease to exist.
Weather patterns are intensifying. Storms, certainly more violent, may also be more numerous, floods and winds more destructive, droughts more severe and protracted, forest fires more common. In 2000, about 25,000 lives were lost in Venezuela's worst flooding in history. In reporting weather events, the phrase "worst on record" is becoming more common. Extremes of heat, cold, rainfall, winds, and forest fires will likely rise. Ironically, to deal with such extremes humans will probably burn more carbon.
Tropical diseases will spread more widely with greater virulence. Minute temperature changes can markedly increase disease-carrying insects and parasites. The dengue virus in South America and Rift Valley fever in Africa and the Middle East have extended their range. Malaria probably will, too. Eastern oyster virus now infects Maine coastal waters, immune when slightly colder. Coral reefs show significant stress. Whole ecologies are changing. In the 1990s, more than forty million Alaskan spruce trees died when warmer temperatures permitted the spruce beetle to multiply.
The science needed to chart earth systems and to predict global climate change is advanced and interdisciplinary. But just as the changes are largely the product of human behavior, so are the ways to adjust to those changes and, if desired, to abate them. Political will and cooperation on an unprecedented scale are needed to lower greenhouse gas levels. On 14 September 2004, Tony Blair, Prime Minister of Great Britain, stated that human activity "is causing global warming at a rate that began as significant, has become alarming, and is simply unsustainable in the long-term. And by long-term ... I mean within the lifetime of my children certainly; and possibly within my own. And by unsustainable, I do not mean a phenomenon causing problems of adjustment. I mean a challenge so far-reaching in its impact and irreversible in its destructive power, that it alters radically human existence."
Many scientists and politicians promote imposing a tax on the carbon content of fuels to encourage conservation and alternate energy sources. More forest "sinks" will help, but forests globally are disappearing, not expanding (see Chapter 6, below). In an agreed international system, countries might sell carbon or carbon dioxide credits (Kyoto provides for the latter). Renewable energy sources and nuclear power will be important. Technology to remove C[O.sub.2] from the atmosphere on a massive scale might become feasible. Treating carbon before its combustion could reduce C[O.sub.2] emissions. Yet exisiting emissions patterns will be hard to curb or reverse. Developing countries require more energy if they are to escape poverty. China, with its vast population, depends on coal more than any other nation. United States citizens make up less than 5 percent of the world's population yet produce 25 percent of its C[O.sub.2]. Increasingly, we are altering major earth systems. This will last for generations and may accelerate. The single most important-and unknown-factor is how human beings will act in the future. Prime Minister Blair warned, "there is no doubt that the time to act is now. It is now that timely action can avert disaster. It is now that with foresight and will such action can be taken without disturbing the essence of our way of life, by adjusting behavior not altering it entirely." If we care about the world that our children will inhabit, we can begin to change the way we live now.
John Houghton, from "The Greenhouse Effect" in Global Warming: The Complete Briefing (1997)
By 1995 many scientists and a significant part of the informed public believed global warming a fact. Evidence since then, including increased temperature readings of the upper as well as the surface atmosphere, confirms this conviction. John Houghton, CoChair of the Intergovernmental Panel on Climate Change (see Further Reading, above) explains the "greenhouse effect," the interconnected series of phenomena that cause global warming and lead to myriad environmental consequences.
The basic principle of global warming can be understood by considering the radiation energy from the sun which warms the Earth's surface and the thermal radiation from the Earth and the atmosphere which is radiated out to space. On average these two radiation streams must balance. If the balance is disturbed (for instance by an increase in atmospheric carbon dioxide) it can be restored by an increase in the Earth's surface temperature.
HOW THE EARTH KEEPS WARM
To explain the processes which warm the Earth and its atmosphere, I will begin with a very simplified Earth. Suppose we could, all of a sudden, remove from the atmosphere all the clouds, the water vapor, the carbon dioxide, and all the other minor gases and the dust leaving an atmosphere of nitrogen and oxygen only. Everything else remains the same. What, under these conditions, would happen to the atmospheric temperature?
The calculation is an easy one, involving a relatively simple radiation balance. Radiant energy from the sun falls on a surface of one square meter in area outside the atmosphere and directly facing the sun at a rate of about 1370 watts-about the power radiated by a reasonably sized domestic electric fire. However, few parts of the Earth's surface face the sun directly and in any case for half the time they are pointing away from the sun at night, so that the average energy falling on one square meter of a level surface outside the atmosphere is only one quarter of this or about 343 watts. As this radiation passes through the atmosphere a small amount, about 6 percent, is scattered back to space by atmospheric molecules. About 10 percent on average is reflected back to space from the land and ocean surface. The remaining 84 percent, or about 288 watts per square meter on average, remains actually to heat the surface-the power used by three good-sized incandescent electric light bulbs.
To balance this incoming energy, the Earth itself must radiate on average the same amount of energy back to space in the form of thermal radiation. All objects emit this kind of radiation; if they are hot enough we can see the radiation they emit. The sun at a temperature of about 6,000°C looks white; an electric fire at 800°C looks red. Cooler objects emit radiation which cannot be seen by our eyes and which lies at wavelengths beyond the red end of the spectrum-infrared radiation (sometimes called long-wave radiation to distinguish it from the short-wave radiation from the sun). On a clear, starry winter's night we are very aware of the cooling effect of this kind of radiation being emitted by the Earth's surface into space-it often leads to the formation of frost.
The amount of thermal radiation emitted by the Earth's surface depends on its temperature-the warmer it is, the more radiation is emitted. The amount of radiation also depends on how absorbing the surface is; the greater the absorption, the more the radiation. Most of the surfaces on the Earth, including ice and snow, would appear "black" if we could see them at infrared wavelengths; that means that they absorb nearly all the thermal radiation which falls on them instead of reflecting it. It can be calculated that, to balance the energy coming in, the average temperature of the Earth's surface must be -6°C to radiate the right amount. This is much colder than is actually the case. In fact, an average of temperatures measured near the surface all over the Earth-over the oceans as well as over the land-averaging, too, over the whole year, comes to about 15°C. Some factor not yet taken into account is needed to explain this discrepancy.
THE GREENHOUSE EFFECT
The gases nitrogen and oxygen, which make up the bulk of the atmosphere (Table 1.1 gives details of the atmosphere's composition), neither absorb nor emit thermal radiation. It is the water vapor, carbon dioxide, and some other minor gases present in the atmosphere in much smaller quantities which absorb some of the thermal radiation leaving the surface, acting as a partial blanket for this radiation and causing the difference of 21°C or so between the actual average surface temperature on the Earth of about 15°C and the figure of -6°C which applies when the atmosphere contains nitrogen and oxygen only. This blanketing is known as the natural greenhouse effect and the gases are known as greenhouse gases. It is called "natural" because all the atmospheric gases (apart from the chlorofluorocarbons-CFCs) were there long before human beings came on the scene....
The basic science of the greenhouse effect has been known since early in the nineteenth century when the similarity between the radiative properties of the Earth's atmosphere and of the glass in a greenhouse was first pointed out-hence the name "greenhouse effect." In a greenhouse, visible radiation from the sun passes almost unimpeded through the glass and is absorbed by the plants and the soil inside. The thermal radiation which is emitted by the plants and soil is, however, absorbed by the glass which re-emits some of it back into the green- house. The glass thus acts as a "radiation blanket" helping to keep the green- house warm.
Excerpted from Environment Copyright © 2008 by Glenn Adelson, James Engell, Brent Ranalli, and K. P. Van Anglen. Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.