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- A droplet of air -- The atmospheric bathtub -- Flapping molecules -- A tea-cozy for earth -- What we can't model -- Protecting climate at a profit -- In God we trust; all others bring data -- More than efficiency -- Why nuclear power can't help -- If Karnataka can do it -- Almost everyone wins
From space, the earth is blue because it is covered mainly by water. However, were it not for certain trace gases in the atmosphere, the earth would be a frigid icy white, and life as we know it would not exist.
Our dependable local star radiates energy in all directions, a bit of which falls on our own planet. As it turns and wobbles and wanders through an unimaginably chilly universe, the earth soaks in solar warmth. Billions of years of this cosmic rotisserie nurtured an enormous diversity of living forms and processes that, through photosynthesis and respiration, helped create an atmosphere. It is that band of gases that keeps life as we know it pleasantly warm.
The earth's atmosphere seems vast to a person sheltered beneath it, but astronauts and cosmonauts see how tissue-thin it is against the black vastness of space. Conservationists Jacques Cousteau and David Brower give us this helpful perspective: If the earth were the size of an egg, then all the water on the planet would be just a drop; all the air, if condensed to the density of water, would be a droplet only one-fortieth as big; and all the arable land would be a not-quite-visible speck of dust. That drop, droplet, and speck are all that make the earth different from the moon.
Incoming solar energy, nearly a fifth of a quadrillion watts, hits the outer atmosphere at about 14,000 times the total rate at which all the people on earth are burning fossil fuels. This ratio makes the amount of fossil fuels being consumed sound insignificant. In fact, though, this burning turns roughly 6-1/2 billion tons a year of carbon--carbon that was fixed by photosynthesis in ancient swamps over tens of millions of years, then locked deep underground as coal, oil, and natural gas--into carbon dioxide. Some advocates argue that even this quantity is insignificant compared to the far vaster amounts of carbon dioxide that are released as part of the natural cycle of life. Indeed, the constant exchange between the growth of green plants and their combustion, digestion, and decay does involve tens of times more annual flow of carbon dioxide than is released by fuel-burning. However, augmenting natural carbon cycles, even with relatively small amounts of fossil carbon, tends to increase disproportionately the amount of CO2 in the atmosphere. An explanation for this phenomenon can be found in your bathroom. If you fill your bathtub exactly as fast as the water runs down the drain, the flow of water in and out will be in equilibrium. But if you open the tap even a little more, your bathtub will ultimately overflow.
Because there is plenty of room for the CO2 we're adding, there is no danger of its overflowing. But as it slowly accumulates, it is gradually double-glazing our home planet. Earth's atmosphere, not counting its water vapor, contains by volume about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.039 percent other trace gases. Nitrogen, oxygen, and argon have no greenhouse effect; thus 99 percent of the atmosphere provides virtually no insulation. Of the atmosphere's main natural constituents, only water, carbon dioxide, and ozone have warming properties. These three warming gases share a common characteristic, they each have three atoms. All molecules absorb energy at the frequencies at which they naturally vibrate. Simple two-atom molecules like nitrogen and oxygen vibrate at high frequencies, like tight little springs, so they don't absorb much of the waste heat that leaves the earth as lower-frequency infrared energy. In contrast, CO2, H2O, and ozone (O3) absorb heat rays especially well, because their three atoms create a triad configuration that can flap, shimmy, and shake at the right rate to absorb and reradiate most of the infrared rays that the warm earth emits. For the same reason, other three-atom pollutants like nitrous oxide (N2O) and sulfur dioxide (SO2) are strong greenhouse gases, too.
Carbon dioxide makes up just 1-2,800th of the atmosphere. Together with the other trace gases, even that tiny amount makes the earth's surface about 59F, warmer, so even a relatively small additional amount can raise the temperature of the planet significantly. Before the industrial revolution, trace gases (including carbon dioxide) totaled 0.028 percent of the atmosphere. Since then, burning fossil fuel, cutting and simplifying forests, plowing prairies, and other human activities have increased that CO2 concentration to 0.036 percent, the highest level in the past 420,000 years, and the CO2 concentration is steadily rising by half a percent per year.
This concentration matters because energy from the white-hot sun is a mixture of roughly half visible light and half invisible infrared heat rays. If the atmosphere had no greenhouse gases, nearly all solar radiation striking the outer edge of the atmosphere would reach the earth's surface, and all of it would promptly escape back into space. That's what makes the airless moon so frigid: It absorbs solar energy four times better than the earth (partly because the moon has no clouds), but its surface averages 63F, colder because there is no atmosphere to hold the heat. In contrast, the earth's atmosphere, like a superwindow, is relatively transparent to most of the radiation coming in from the sun but is nearly opaque to the very long wavelengths of infrared rays that radiate back to space. The atmosphere holds that heat like a semi-transparent blanket. The resulting exchange of energy back and forth between the atmosphere and the earth is 47 percent larger than the solar energy arriving from the sun, which is why the earth's surface averages about 59F rather than 0F. It's also why life is possible. Those few hundredths of one percent of the atmosphere that are carbon dioxide play a critical role in this heat balance.
The warmed surface of the earth tries to radiate its heat back into space, just as a hot teapot radiates heat until it gradually cools to the temperature of the kitchen. Putting more carbon dioxide into the air is like putting a tea-cozy over the pot: It blocks the escaping heat. But this particular teapot is still on the stove, as more solar heat is added daily. The better the tea-cozy blocks the escaping heat, while the stove continues to add more heat at the same rate, the hotter the tea becomes. The atmosphere works in the same way. Suppose we add more heat-trapping CO2 to the atmosphere. Then more of the outgoing infrared rays get absorbed and reradiated downward to warm the earth's surface. The air above the surface is also warmed, which enables it to hold more water vapor, which means even more greenhouse heat-trapping and possibly more clouds. Depending on their height, latitude, and other factors, those additional clouds may further warm the earth beneath them or may cool it by bouncing away more incoming sunlight. Either way, more water vapor in the air means more precipitation. Hotter air makes the water cycle and the weather machine run faster, which leads to more intense storms and more rainfall. In round numbers, each Fahrenheit degree of global warming will increase global mean precipitation by about one percent, but some places will get much more.
Over the past century, as accumulating greenhouse gases have trapped two to three more watts of radiant heat over each average square meter of the earth, its surface has become about 1F warmer. Amazing the climatologists, in the single year 1998�the hottest year since record-keeping began in 1860, and, according to indirect evidence, in the past millennium�the earth's average temperature soared by another quarter of a Fahrenheit degree, to about 1-1/4 F� warmer than the 1961�90 average. Each of the 12 months through September 1998 set a new all-time monthly high-temperature record. Seven of the ten hottest years in the past 130-odd years occurred in the 1990s�the rest after 1983�despite such strong countervailing forces as the eruption of Mt. Pinatubo, a dip in solar energy, and the depletion of stratospheric ozone, a greenhouse gas. In 1998, at least 56 countries suffered severe floods, while 45 baked in droughts that saw normally unburnable tropical forests go up in smoke from Mexico to Malaysia and from the Amazon to Florida. Many people's intuition that weather is shifting and becoming more volatile is confirmed by meteorological measurements. Spring in the Northern Hemisphere is coming a week earlier; the altitude at which the atmosphere chills to freezing is rising by nearly 15 feet a year; glaciers are retreating almost everywhere.
Warming the surface of the earth changes every aspect of its climate, especially the heat-driven engine that continually moves vast seas of air and water like swirls in hot soup. Some places get hotter, others colder, some wetter, others drier. Rainfall patterns shift, but when it does rain, it tends to rain more heavily. A warmer earth probably also means more volatile weather with more and worse extreme events of all kinds. Nobody knows exactly how these changes will play out, especially in a particular locality, but some of the general trends are already apparent.
Warmer oceans, for example, can cause currents to shift and change, more frequent and severe tropical hurricanes and typhoons to form, and perhaps more frequent or more intense El Ni�o events to occur. Warmer oceans kill coral reefs (which when healthy metabolize and thus sequester CO2). The warmed ocean can actually release more CO2, just as happens when you open a soda warmed by the sun. This is important because oceans contain about 60 times as much CO2 as the atmosphere does. Warmer soil, especially at high latitudes, speeds up plant decomposition, releasing more CO2. It also means drier soil and hence shifts in vegetation. In any given ecosystem, more CO2 increases growth of those plants that can best take up more CO2, but at the competitive expense of other plants. This unpredictably changes the composition of plant populations, hence that of animal populations and soil biota. Different vegetation also alters the land's ability to absorb sunlight and to hold rainwater. This can affect erosion patterns under heavier rains. Parched forests, bad grazing practices, and late rains cause more forest and grassland fires, more carbon release, and more smoke, as happened in Southeast Asia and Australia in 1997�98.
As the planet traps more heat, it drives more convection that transports surplus heat from equatorial to the polar areas (heat flows from hotter to colder), so temperature changes tend to be larger at the poles than at midlatitudes. Warmer poles mean changes in snowfall, more melting icecaps and glaciers (five Antarctic ice sheets are already disintegrating), and more exposed land and oceans. Ice-free oceans, being dark, absorb more solar heat and therefore don't refreeze as readily. Rising amounts of runoff from high-latitude rivers lower ocean salinity. This can shift currents, including the Gulf Stream, which makes northern Europe abnormally cozy for its Hudson's Bay latitude, and the Kuroshio Current, which likewise warms Japan. Warmer oceans raise sea levels, as ice on land melts and warmer water expands; sea levels have risen by about four to ten inches in the past century. Warmer oceans probably bring more and worse storms, more loss of coastal wetlands that are the nurseries of the sea, and more coastal flooding. "Thirty of the world's largest cities," writes Eugene Linden, "lie near coasts; a one-meter rise in the oceans ...would put an estimated 300 million people directly at risk." That would include 16 percent of Bangladesh�a country that spent much of the summer of 1998 up to two-thirds underwater.
Now consider the contributions of the many other trace gases that also absorb infrared rays. Methane comes from swamps, coal seams, natural-gas leaks, bacteria in the guts of cattle and termites, and many other sources. Its concentration has risen since the eighteenth century from 700 to 1,720 parts per billion and is increasing at a rate of about one percent a year. Methane is a greenhouse gas 21 times more potent per molecule than CO2. Nitrous oxide is over 100 times as potent as CO2; CFCs (the same synthetic gases already being phased out because they also destroy stratospheric ozone), hundreds to thousands of times; their partly or completely fluorinated substitutes, hundreds to tens of thousands of times. Near-surface ozone and nitric oxide, familiar constituents of smog, absorb infrared, too. Together, all these gases have had a heat-trapping effect about three-fourths as significant as that of CO2 alone.
Many trace gases can react chemically with others and with one another to make new gases. The resulting 30-odd substances can undergo more than 200 known reactions. These occur differently at different altitudes, latitudes, seasons, concentrations, and, of course, temperatures, which is what the very presence of the gases affects. How various gases dissolve in or react with the oceans also depends on temperatures, concentrations, and currents. Warmer oceans, for example, hold less nitrate, slowing the growth of carbon-absorbing phytoplankton. Also, if high-latitude tundras get much warmer, ice-like compounds called methane hydrates trapped deep beneath the permafrost and offshore in the Arctic could ultimately thaw and start releasing enormous amounts of methane�more than ten times what is now in the atmosphere. Long before that could happen, though, even slight changes in Arctic bogs' water levels can increase their methane production by 100-fold. Meanwhile, the mass of frigid air above the North Pole could get even colder and more persistent, favoring ozone-depleting chemical reactions that could destroy up to 65 percent of Arctic ozone�a deeper loss than has occurred in the Antarctic.
The dance of heat between sun, sky, and earth is affected not only by transparent gases and clouds but also by dust from volcanoes, deserts, and the burning of fossil fuel. Most dust, like the clouds of sulfate particles that are also produced by fossil-fuel combustion, tends partly to offset CO2's heat-trapping effect. So far, on a global basis the dust has approximately canceled the warming effect of additional non-CO2 greenhouse gases.
The atmosphere, ocean, land, plant, and animal systems all interact in countless complicated ways, not all of which are yet known and many of which are not yet fully understood. Most of the interactions are nonlinear, and some appear to be unstable. Modern computer models are sophisticated enough to be able to model some historic shifts in climate quite well, but they're far from perfect, and getting them close to perfection will take longer than performing the global climate experiment already under way. Many scientists suspect that relatively small changes in certain forces that drive the climate�notably CO2 concentrations, especially if they happen fast enough�may trigger large and sudden changes in the world's weather, for example by shifting ocean currents. Such changes could even lead to the onset of ice ages in mere decades: They seem to have happened this abruptly before, and therefore must be possible, but such situations are difficult to model reliably.
A few scientists believe there might be a number of still unknown climate-stabilizing mechanisms at work. However, no important ones have yet been found, and all the promising candidates have been eliminated one by one. Instead, almost all the known climate feedback mechanisms appear to be positive�warmer begets warmer still. Many uncertainties remain, but uncertainty cuts both ways. The climate problem may be less serious than most scientists fear, or it could be even worse. Stratospheric ozone depletion turned out to be worse, once the unexpected "ozone hole" over the Antarctic was noticed and found to be growing rapidly. It required emergency action in the 1980s to phase out the proven culprit�CFCs and a few related compounds, such as Halon in fire extinguishers.
What's beyond doubt is that the composition of the atmosphere is now being altered by human activity, more rapidly than it's changed at any time in at least the past 10,000 years. The present state of knowledge suggests that, even if emission rates are reduced somewhat below their 1990 levels, we will still gradually reach about triple the preindustrial CO2 concentration. If the world's nations wanted to stabilize the atmosphere in its present disrupted state, they would need to cut CO2 emissions immediately by about three-fifths. To return to preindustrial levels, we'd have to reduce emission rates promptly to severalfold below current ones. Further research may disclose either bigger safety margins, allowing that ambitious goal to be relaxed, or smaller ones, requiring it to be tightened. For now, no one knows what might constitute a "safe" rate of, or limit to, changing the atmosphere's CO2 concentration. What is clear is that the transformations now under way are part of a risky global experiment, and that their effects on the planet's life-support systems, whatever they turn out to be, may be irreversible.
A broad scientific consensus has already acknowledged the existence of a potentially serious climate problem. About 99.9 percent of the world's qualified climate scientists agree that the infrared-absorbing gases that human activity is releasing into the air are cause for concern�if not now, then soon. Most believe that those emissions are probably already beginning to disrupt the earth's climate in observable ways. The many remaining scientific uncertainties create plenty of room for interpretation about exactly what might happen, how, and when, let alone its effects on people and other life-forms. All these issues are vigorously debated among thousands of climate scientists because that's how science works: From debate, observation, hypothesis, experiment, mistake, discovery, more debate, and reassessment ultimately emerges truth. The laypeople who don't like what the science is predicting, or who don't understand the scientific process, can easily seize on details of that debate and conclude that climate science is too immature and uncertain a discipline to support any broad conclusions yet. They'd be wrong.
However, the terms and outcome of the climate-science debate don't ultimately matter. Because of the resource productivity revolution, the actions and requirements needed to protect the climate are profitable for business right now, no matter how the science turns out and no matter who takes action first. Arguments that it would be too expensive and economically harmful to mitigate the rate of increase in greenhouse gases are upside down. It costs less to eliminate the threat to our global climate, not more.
(End of excerpt)
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