An Ocean of Air (20 page)

Jet streams tend to occur at either side of Ferrel's stormy westerlies, in the high atmosphere; where tropical air meets the cooler air of the middle latitudes; and again where middle-latitude air collides with the freezing atmosphere of the polar regions. Take the northern hemisphere jet streams. In each case, the big contrast in temperature between these two bodies of air sends the southern air roaring northward, which according to Ferrel's "north turns right" rule means that it whips around to the east. Each of these two jets thrashes about in complex ways. Sometimes the two of them merge to make one gigantic jet in each hemisphere; sometimes, they all but disappear. They are strongest in the winter, when the temperature contrast between equator and pole is the greatest.

Storms form in the same regions as jet streams because they, too, feed off the strong temperature contrasts, and the jets then steer them around the world. The rain contained in these storms is one of the chief engines of climate, the means by which our air can redistribute its resources—taking from each parcel of air according to its ability to give, giving to each according to its needs.

Though our atmosphere contains only a few hundredths of a percent of all the water on Earth, it is by far the most active transporter. An average molecule of water will stay locked in oceans and ice sheets for hundreds or thousands of years, but one that is soaked up into the atmosphere will be carried aloft and then rained out again in only ten days.

Life could not survive anywhere on Earth's land surface without rainfall, for all living things need water, and without the atmosphere's helpful
redistribution mechanisms we would be confined to the seas. But more than that, the storms that bring water also carry heat.

When air soaks up water from the ocean, it uses energy to rip the water molecules apart from one another and turn them into a disintegrated gas. When the molecules reunite to form raindrops they give out energy, which is what feeds the storms. Heat and water are intimately connected, and the global winds redistribute both. (The same principle is behind sweating. When you sweat, glands take water from the interior of your body and pour it out onto the surface. This water then gradually evaporates into the air around you, taking with it your excess heat energy, to be delivered via air and rain, to somewhere else that needs it more.)

Earth's gigantic wind systems have been performing this feat for billions of years, producing many different patterns of global climate. The winds adapt to subtle shifts in the gradients of temperature and the amounts of available water to produce worlds that have always been habitable but have sometimes looked quite different from the one we have today. However, we humans have evolved in a world with one specific set of handouts, and one specific resulting climate. And our own particular pattern of redistribution may soon change. Many now fear that global warming will interfere with the way the winds deposit their loads. Warmer air can hold more water before it must be shed as rain, perhaps bringing droughts to some regions. More water in the air means more energy, so storms may be fiercer. As the polar regions warm, jet streams may shift their positions; some think that the widespread fires in North America in 2002 were a symptom of the jet stream shifting north and taking its rainstorms with it.

But even if all this does take place, Earth will probably adapt. There are still likely to be lakes and rivers and reservoirs at least somewhere on the planet. Our enveloping air has effected this transformation of the Earth for more than four billion years, and there's no reason it should stop now. (Whether the adapted Earth will still be a comfortable, or even feasible, place for large numbers of humans to live is quite another matter.)

So far, we have seen our ocean of air all in the guise of transformer. But it has another role, just as crucial for the survival of Earth's creatures. For the life the air engenders is still vulnerable. Space is filled with hazards that, if they ever reached the planet's surface, would put us all in grave peril.

Here again, our atmosphere intercedes for us. Above the clouds, layer after layer of air provide bulwarks against the ravages of space. And the very first of those protective layers was nearly destroyed almost before we knew it was there.

OZONE IS A BEAUTIFUL GAS.
Unlike its closest relative, oxygen, which is invisible, ozone is a vibrant shade of blue. When Dublin scientist W. M. Hartley began working on the gas in 1881, he was enchanted by its color, "as blue as the sky on a brilliant day." And though some people were inclined to find the smell of ozone disagreeably pungent, Hartley thought it fresh, as after a great thunderstorm when the world has been washed clean: "Ozonised air gave a very distinct odour, quite unmistakable, but quite reminding one of the air on the South Downs during a south-west breeze."

Hartley was curious about this new gas, discovered only forty years earlier. It existed naturally in the environment, but apparently only in tiny quantities and special circumstances, such as after a lightning strike. Some researchers had recently discovered that it was made of oxygen atoms; but where the molecules of normal oxygen contain only a pair of atoms (O2), ozone molecules have a third (O3). This additional atom seemed to make ozone even more reactive than oxygen. Breathing it was an uncomfortable experience. It caused chest pains and irritation, and small animals such as mice couldn't survive in it for long. (At ground level in the modern world, ozone is a component of automobile smog, and hence a major irritant for asthmatics.)

But that wasn't the whole story. Hartley was about to discover that high in the atmosphere, ozone plays a very different part in our lives. Starting some 20 miles above the ground, it forms a protective layer, the first of the air's three silver linings that shield every living creature from the hostility of space.

He was led to this discovery by the curious observation that some of the sun's rays were missing. Recall that the sun throws out more kinds of
light than we humans can see. Beyond the red end of the rainbow lie the long infrared light waves that are responsible for warming our planet. Their successive peaks and troughs are too widely spaced to be seen by our limited eyes. But infrared light also has a high-energy cousin called ultraviolet, which appears beyond the blue end of the rainbow and whose waves are too short for us to see.

Though our eyes are blind to these extra rays, by Hartley's time there were plenty of instruments that could spot them. And there lay the problem. The infrared rays were there all right, but the ultraviolet ones suddenly stopped. Visible light cuts off at a wavelength of about four hundred nanometers (which is four ten-thousandths of a meter). Anything shorter than that is ultraviolet light, and you'd expect ultraviolet rays from the sun at every wavelength from four hundred all the way down to two hundred nanometers. But below 293 nanometers, there was nothing. Or at least nothing that arrived at Earth's surface.

Either the sun wasn't putting out these highest-energy, shortest-wavelength ultraviolet rays or something was stopping them from reaching us.

Hartley was thinking about this problem when he noticed that ozone gas had a tendency to absorb ultraviolet rays. What, he wondered, would happen if he tried shining a full complement of ultraviolet wavelengths through a bright blue tube of ozone gas? The answer was that the ozone clipped off the end of the ultraviolet rainbow. Nothing shorter than 293 nanometers made it through to the other side. Hartley concluded his paper describing these experiments with the following words, written in what was for him an unusually formal manner:

The foregoing experiments and considerations have led me to
the following conclusions:
1st That ozone is a normal constituent of the higher atmosphere
2nd That it is in larger proportion there than near the earth's surface
3rd That the quantity of atmospheric ozone is quite sufficient to account for the limitation of the solar spectrum in the ultraviolet region

He was right. Five billion tons of ozone float above our heads, trapping the highest-energy ultraviolet rays before they make it down to the surface. The lowest-energy ultraviolet rays, the ones that our ozone frontier-guards let through, are quite good for humans. They encourage our skin to make vitamin D, which we need to avoid rickets and other bone diseases, and they also give some of us golden brown tans. But if the ones it trapped were allowed to fall freely to ground, they would be highly dangerous. These forms of UV light, called UVB and UVC, attack whatever they touch. They weaken the human immune system; they cause skin cancer and cataracts; and they destroy algae, which are the most fundamental members of the ocean food chain.

Our ozone layer protects us so comfortably and effectively that we could easily never know the dangers that lie just a few miles above us. It works like a minefield: Whenever an ozone molecule is touched by an ultraviolet ray, it explodes, firing off one of its three oxygen atoms. But this is a minefield that reforms itself constantly. The shrapnel from the explosion—a stray oxygen atom and an ordinary oxygen molecule—recombine. And when they do, the ozone is born again.

This much was figured out by a British chemist named Sidney Chapman in the 1930s fifty years after Hartley's discovery. But at the very time that he was writing down the equations showing how powerful and vital the ozone layer is, another chemist was creating a chemical that would come close to destroying it. For, like many things that are strong, the ozone layer is also vulnerable.

***

In 1920s America, a certain industrialist was preparing to make another of his inventions. Thomas Midgley was a jovial man, full of enthusiasm and energy. He had hordes of friends, and—amazingly, given his many successes—scarcely any enemies. His face, round like a full moon, beamed with bonhomie, especially when he found a new engineering puzzle to solve. Even in his spare time he was captivated by mechanical problems. When he was walking in the countryside, he spent half his time supine,
trying to figure out the principles behind the construction of anthills. When he took up golf and discovered the poor quality of the greens, he began experimenting at home with new kinds of grasses. He was a born inventor.

It's not surprising that Midgley had an inventor's eye—his whole family loved to experiment. His mother's father had devised the circular saw, and his own father held a number of patents for new kinds of tires and bicycle wheels. Midgley's first job was in "Inventions Department No. 3" of the National Cash Register Company in Dayton, Ohio, and then in 1916 he moved to the research division of the General Motors Company. It was there that he would make his most famous inventions, materials that would prove to be useful, powerful, and ultimately deadly.

For though he didn't know it at the time, Midgley was destined to be terribly unlucky with his inventions. One of the first things he did at General Motors was to recommend putting lead in gasoline. He had a good reason for this—indeed, it was hailed as an ingenious solution to a most annoying problem. Cars and planes were relatively recent inventions, and all attempts to make their engines more efficient came up against the same problem: Uneven combustion meant that they made an infuriating knocking sound and operated poorly. Midgley wanted to find something that he could add to the gasoline to make it burn more evenly. At first, he had little success. He tried everything "from melted butter and camphor to ethyl acetate and aluminum chloride ... and most of them had no more effect than spitting in the Great Lakes." (He did discover that compounds containing tellurium and selenium seemed to work, but they had a bizarre side effect, making the workers reek with the smell of garlic.)

Finally, in December 1921, after working his way through thousands of compounds, Midgley discovered that adding lead to the mix solved everything. He had to overcome a certain amount of prejudice from consumers who thought that lead in gasoline might be dangerous. (It is. It accumulates in humans and causes several debilitating diseases, which is why it is now banned.) But at the time, Midgley's well-meaning arguments prevailed. The first leaded gasoline went on sale in 1923, and it quickly became universal. Engines in cars and planes could now work much more efficiently, and Midgley was on his way to becoming a hero.

Midgley's next invention arose from a problem that came to him from Frigidaire, the refrigeration division of General Motors. Mechanical refrigeration was a recent arrival on the technological scene. Before then, ice had to be shipped down from Canada to provide a coolant of sorts, but it was expensive, weather-dependent, and not widely available. Hospital wards in the southern United States were often unbearable during the summer, with the heat killing off as many people as actual illnesses. Food spoiled rapidly, and "tropical" diseases like yellow fever and malaria were still rampant there. So mechanical refrigeration seemed like a miracle. Buildings could be air-conditioned, families could keep food for days without it spoiling, and people could make their own ice even in midsummer.

Refrigerators work by successively liquefying and re-evaporating the material inside their pipes. The material starts out as a gas, but in the pipes outside the fridge the gas is squeezed until it turns into a liquid—which releases heat energy and explains why the backs of refrigerators get hot. This liquid is then carried inside the fridge, where it is allowed to expand until it turns back into a gas. This process is the exact opposite of the liquefaction. It soaks up heat energy from its surroundings, cooling down the fridge in the process.

The problem lay in the choice of material that could be so readily squeezed into a liquid and then sprayed back into a gas. To date, every refrigerant that anyone tried had some kind of health hazard attached—some were toxic, some were flammable, and some were both. As long as these gases stayed safely in their closed pipes, that wasn't a problem. But somewhere, sometime, there would be a leak—and that's where the trouble started. By 1929 Frigidaire had sold one million domestic refrigerators, and the accident toll was mounting. People moved their fridges out onto the back porch. After a fatal leak in a Cleveland medical center, hospitals scarcely dared use them at all. Frigidaire's engineers even suggested returning exclusively to the first refrigerant they had tried—sulfur dioxide. Yes, it was highly poisonous, but at least its irritating choking smell gave immediate warning of danger.