Billions & Billions (15 page)

About 30 percent of all U.S. oil imports comes from the Persian Gulf. In some months, more than half of U.S. oil is imported. Oil constitutes more than half of all U.S. balance of payments deficits. The U.S. spends over a billion dollars a week in oil imports from abroad. Japan’s oil import bill is about the same. China—with burgeoning consumer demand for autos—may reach the same level early in the twenty-first century. Similar numbers apply to Western Europe. Economists spin scenarios in which increases in oil prices induce inflation, higher interest rates, diminished investment in new industry, fewer jobs, and economic recession. It may not happen, but it is a possible consequence of our addiction to oil. Oil drives nations into policies they might otherwise find unprincipled or foolhardy. Consider, for example, the following (1990) comment from the syndicated columnist Jack Anderson, expressing a widely held opinion: “As unpopular as the notion is, the United States must continue to be policeman for the globe. On a purely selfish level, Americans need what the world has—oil being the pre-eminent need.” According to Bob Dole, the Senate minority leader at the time, the Persian Gulf War—which put over 200,000 young American men and women at risk—was undertaken “for one reason only: O-I-L.”

As I write, the nominal cost of crude oil is almost $20 a barrel, while the world’s authenticated or “proven” petroleum
reserves are almost a trillion barrels. Twenty trillion dollars is four times the U.S. national debt, the largest in the world. Black gold, indeed.

The global production of petroleum is about 20 billion barrels a year, so each year we use up about 2 percent of the proven reserves. You might think we’re going to run out pretty soon, maybe in the next 50 years. But we keep finding new reserves. Previous predictions that we would run out of petroleum by such-and-such a date have always proved baseless. There is a finite amount of oil, gas, and coal in the world, it’s true. There were only so many of those ancient organisms that contributed their bodies for our comfort and convenience. But it seems unlikely we will run out of fossil fuels soon. The only problem is, it’s more and more expensive to find new and unexploited reserves, the world economy can go into fibrillation if oil prices are made to change quickly, and countries go to war to get the stuff. Also, of course, there’s the environmental cost.

The price we pay for fossil fuels is measured not just in dollars. The “satanic mills” of England in the early years of the Industrial Revolution polluted the air and caused an epidemic of respiratory disease. The “pea soup” fogs of London, so familiar to us from dramatizations of Holmes and Watson, Jekyll and Hyde, and Jack the Ripper and his victims, were deadly domestic and industrial pollution—largely from burning coal. Today, automobiles add their exhaust fumes, and our cities are plagued by smog—which affects the health, happiness, and productivity of the very people generating the pollutants. We also know about acid rain and the ecological turmoil caused by oil spills. But the prevailing opinion has been that these penalties to health and environment were more than balanced by the benefits that fossil fuels bring.

Now, though, the governments and peoples of the Earth are gradually becoming aware of yet another dangerous consequence of the burning of fossil fuels: If I burn a piece of coal or a gallon of petroleum or a cubic foot of natural gas, I’m combining the carbon in the fossil fuel with the oxygen in the air. This chemical reaction releases energy locked away for perhaps 200 million years. But in combining a carbon atom, C, with an oxygen molecule, O
₂
, I also synthesize a molecule of carbon dioxide, CO
₂

C + O
₂
→ CO
₂

And CO
₂
is a greenhouse gas.

—

What determines the average temperature of the Earth, the planetary climate? The amount of heat trickling up from the center of the Earth is negligible compared with the amount falling down on the Earth’s surface from the Sun. Indeed, if the Sun were turned off, the temperature of the Earth would fall so far that the air would freeze solid, and the planet would be covered with a layer of nitrogen and oxygen snow 10-meters (30-feet) thick. Well, we know how much sunlight is falling on the Earth and warming it. Can’t we calculate what the average temperature of the Earth’s surface ought to be? This is an easy calculation—taught in elementary astronomy and meteorology courses, another example of the power and beauty of quantification.

The amount of sunlight absorbed by the Earth has to equal on average the amount of energy radiated back to space. We don’t ordinarily think of the Earth as radiating into space, and when we fly over it at night we don’t see it glowing in the dark
(except for cities). But that’s because we’re looking in ordinary visible light, the kind to which our eyes are sensitive. If we were to look beyond red light into what’s called the thermal infrared part of the spectrum—at 20 times the wavelength of yellow light, for example—we would see the Earth glowing in its own eerie, cool infrared light, more in the Sahara than Antarctica, more in daytime than at night. This is not sunlight reflected off the Earth, but the planet’s own body heat. The more energy coming in from the Sun, the more the Earth radiates back to space. The hotter the Earth, the more it glows in the dark.

What’s coming in to warm the Earth depends on how bright the Sun is and how reflective the Earth is. (Whatever isn’t reflected back into space is absorbed by the ground, the clouds, and the air. If the Earth were perfectly shiny and reflective, the sunlight falling on it wouldn’t warm it up at all.) The reflected sunlight, of course,
is
mainly in the visible part of the spectrum. So set the input (which depends on how much sunlight the Earth absorbs) equal to the output (which depends on the temperature of the Earth), balance the two sides of the equation, and out comes the predicted temperature of the Earth. A cinch! Couldn’t be easier! You calculate it, and what’s the answer?

Our calculation tells us that the average temperature of the Earth should be about 20° Celsius below the freezing point of water. The oceans ought to be blocks of ice and we all ought to be frozen stiff. The Earth should be inhospitable to almost all forms of life. What’s wrong with the calculation? Did we make a mistake?

We didn’t exactly make a mistake in the calculation. We just left something out: the greenhouse effect. We implicitly assumed that the Earth had no atmosphere. While the air is transparent at ordinary visible wavelengths (except for places like Denver and Los Angeles), it’s much more opaque in the thermal infrared part
of the spectrum, where the Earth likes to radiate to space. And that makes all the difference in the world. Some of the gases in the air in front of us—carbon dioxide, water vapor, some oxides of nitrogen, methane, chlorofluorocarbons—happen to absorb strongly in the infrared, even though they are completely transparent in the visible. If you put a layer of this stuff above the surface of the Earth, the sunlight still gets in. But when the surface tries to radiate back to space, the way is impeded by this blanket of infrared absorbing gases. It’s transparent in the visible, semi-opaque in the infrared. As a result the Earth has to warm up some, to achieve the equilibrium between the sunlight coming in and the infrared radiation emitted out. If you calculate how opaque these gases are in the infrared, how much of the Earth’s body heat they intercept, you come out with the right answer. You find that on average—averaged over seasons, latitude, and time of day—the Earth’s surface must be some 13°C above zero. This is why the oceans don’t freeze, why the climate is congenial for our species and our civilization.

Our lives depend on a delicate balance of invisible gases that are minor components of the Earth’s atmosphere. A little greenhouse effect is a good thing. But if you add more greenhouse gases—as we have been doing since the beginning of the Industrial Revolution—you absorb more infrared radiation. You make that blanket thicker. You warm the Earth further.

For the public and policymakers, all this may seem a little abstract—invisible gases, infrared blankets, calculations by physicists. If difficult decisions on spending money are to be made, don’t we need a little more evidence that there really
is
a greenhouse effect and that too much of it can be dangerous? Nature has kindly provided, in the character of the nearest planet, a cautionary reminder. The planet Venus is a little closer to the Sun than the Earth, but its unbroken clouds are so bright that the
planet actually absorbs less sunlight than the Earth. Greenhouse effect aside, its surface ought to be cooler than the Earth’s. It has very closely the same size and mass as the Earth, and from all this we might naively conclude that it has a pleasant Earth-like environment, ultimately suitable for tourism. However, if you were to send a spacecraft through the clouds—made, by the way, largely of sulfuric acid—as the Soviet Union did in its pioneering
Venera
series of exploratory spacecraft, you would discover an extremely dense atmosphere made largely of carbon dioxide with a pressure at the surface 90 times what it is on Earth. If now you stick out a thermometer, as the
Venera
spacecraft did, you find that the temperature is some 470°C (about 900°F)—hot enough to melt tin or lead. The surface temperatures, hotter than those in the hottest household oven, are due to the greenhouse effect, largely caused by the massive carbon dioxide atmosphere. (There are also small quantities of water vapor and other infrared absorbing gases.) Venus is a practical demonstration that an increase in the abundance of greenhouse gases may have unpleasant consequences. It is a good place to point ideologically driven radio talk-show hosts who insist that the greenhouse effect is a “hoax.”

As there get to be more and more humans on Earth, and as our technological powers grow still greater, we are pumping more and more infrared absorbing gases into the atmosphere. There are natural mechanisms that take these gases out of the air, but we are producing them at such a rate that we are overwhelming the removal mechanisms. Between the burning of fossil fuels and the destruction of forests (trees remove CO
₂
and convert it to wood), we humans are responsible for putting about 7 billion tons of carbon dioxide into the air every year.

You can see in the figure on
this page
the increase with time of carbon dioxide in the Earth’s atmosphere. The data come
from the Mauna Loa atmospheric observatory in Hawaii. Hawaii is not highly industrialized and is not a place where extensive forests are being burned down (putting more CO
₂
in the air). The increase in carbon dioxide with time detected over Hawaii comes from activities all over the Earth. The carbon dioxide is simply carried by the general circulation of the atmosphere worldwide—including over Hawaii. You can see that every year there’s a rise and fall of carbon dioxide. That’s due to deciduous trees, which, in summer, when in leaf, take CO
₂
out of the atmosphere, but in winter, when leafless, do not. But superimposed on that annual oscillation is a long-term increasing trend, which is absolutely unambiguous. The CO
₂
mixing ratio has now exceeded 350 parts per million—higher than it’s ever been during the tenure of humans on Earth. Chlorofluorocarbon increases have been the quickest—by about 5 percent a year—because of the worldwide growth of the CFC industry, but they are now beginning to taper off.
^*
Other greenhouse gases, methane for instance, are also building up because of our agriculture and our industry.

Well, if we know by how much greenhouse gases are building up in the atmosphere and we claim to understand what the resulting infrared opacity is, shouldn’t we be able to calculate the increase of temperature in recent decades as a consequence of the buildup of CO
₂
and other gases? Yes, we can. But we have to be careful. We must remember that the Sun goes through an 11-year cycle, and that how much energy it puts out changes a little over its cycle. We must remember that volcanos occasionally blow their tops and inject fine sulfuric acid droplets
into the stratosphere, thereby reflecting more sunlight back into space and cooling the Earth a little. A major explosion can, it is calculated, lower the world temperature by nearly a Celsius degree for a few years. We must remember that in the lower atmosphere there is a pall of tiny sulfur-containing particles from industrial smokestack pollution that—however damaging to people on the ground—also cools the Earth; as well as windblown mineral dust from disturbed soils that has a similar effect. If you make allowances for these factors and many more, if you do the best job climatologists are now capable of doing, you reach this conclusion: Over the twentieth century, due to the burning of fossil fuels, the average temperature of the Earth should have increased by a few tenths of a degree Celsius.

Naturally you would like to compare this prediction with the facts. Has the Earth’s temperature increased at all, especially by this amount, during the twentieth century? Here again you must be careful. You must use temperature measurements made far from cities, because cities, through their industry, and their relative lack of vegetation, are actually hotter than the surrounding countryside. You must properly average out measurements made at different latitudes, altitudes, seasons, and times of day. You must allow for the difference between measurements on land and measurements on water. But when you do all this, the results seem consistent with the theoretical expectation.

The Earth’s temperature has increased a little, less than a degree Celsius, in the twentieth century. There are substantial wiggles in the curves, noise in the global climatic signal. The ten hottest years since 1860 have all occurred in the ’80s and early ’90s—despite the cooling of the Earth from the 1991 explosion of the Philippine volcano Mount Pinatubo. Mount Pinatubo introduced 20 to 30 megatons of sulfur dioxide and aerosols into the Earth’s atmosphere. Those materials completely circled the Earth in about three months. After only two months they had covered about two-fifths of the Earth’s surface. This was the second most violent volcanic eruption in this century (second only to that of Mount Katmai in Alaska in 1912). If the calculations are right and there are no more big volcanic explosions in the near future, by the end of the ’90s the upward trend should reassert itself. It has: 1995 was marginally the hottest year on record.