An Ocean of Air

by Gabrielle Walker

  And now came the real test. Could he use the high winds to fly faster than the plane should conceivably be capable of flying, fast enough that his doubters would have to believe him? His first attempt came very close to disaster.

  On February 22, 1935, Post took off from Burbank airport in California, bound for the East Coast. He climbed almost straight up, five miles high. But then, at 24,500 feet, he noticed a problem. The oil pressure suddenly dropped. If he didn't cut off the engine, every bearing in the plane would jam. Post began to drop in altitude, looking for somewhere to land the plane. He was only thirty-five minutes out of Burbank, but there was nothing like a runway in sight. Worse, he had jettisoned his landing gear to make the plane more streamlined. He would have to land on the plane's specially reinforced fuselage, and it was surely going to be rough. But then Post spotted a dry lake bed and, with true flying genius, managed to bring the plane down and to a safe halt.

  He struggled his way out of the cockpit, but there was no way he could remove the pressure suit on his own. Hampered by the thick cloth, Post couldn't even reach around the back to unscrew his helmet. In the end he walked to a road, where a motorist was tinkering with his broken-down car. It must have been quite a sight. "The man's knees buckled and he almost fell over. He ran around to the back of his auto and peered at me. I had a time calming him down but I finally succeeded and he helped me out of my oxygen helmet. 'Gosh fellow,' he exclaimed when he found his voice, 'I was frightened stiff. I thought you had dropped out of the moon, or somewhere.'"

  The two men walked together to get help. But it was only when the plane was brought back to Burbank for inspection that Post discovered what had gone wrong. Two pounds of metal filings and dust had deliberately been poured into the oil tank. Someone had tried to kill him.

  Wiley Post, daredevil, ex-parachute jumper and highway robber, wasn't the sort to scare easily. On March 5, 1935, he climbed back into a plane that had been meticulously checked and set off again from Burbank. This time, all went well—at least at first. But when he reached Ohio, Post realized that he was almost out of oxygen. He had no choice but to drop back down to lower altitudes and land at Cleveland airport. Still, he had surely done enough. The Winnie Mae had flown two thousand miles in seven hours, nineteen minutes. That made her average speed nearly 280 miles an hour, which was at least one hundred miles an hour faster than she should be able to fly.

  But somehow it still didn't convince people. Post was simply too unreliable a witness to overcome their prejudice against the idea of high winds in clear air. Perhaps if he could just get all the way to the East Coast ... But though he tried again, twice, mechanical failure kept bringing him down. According to one report, in the first of these attempts his helmet fogged up so much he had to clear it by scraping it with the tip of his nose. When his nose was so raw that it had smeared the glass with blood, he had to land.

  It's a pity that nobody believed Wiley Post. He would die in a flying accident in Alaska (apparently an innocent one) years before the world realized he had been right. And in the meantime, human ignorance of his discovery would lead to more than one tragedy.

  ***

  What Wiley Post had called "high winds" we now know as jet streams. These fast-flowing rivers of air circle the world in both hemispheres. They're not always invisible. Sometimes they drag white cirrus clouds along for the ride, and the long, thin trail they leave can be seen from space. Mount Everest pokes up into one stream that blows from west to east over Asia, which is why many portraits of the mountain show a trail of blowing snow over the eastern face. Jet streams are only a few hundred miles across and perhaps only a few miles deep, but they are fierce. Whipping along at speeds of more than one hundred and sometimes as much as three hundred miles per hour, they are among the strongest winds in the world: faster than hurricanes, almost as fast as tornadoes, but with an influence that is much more far-reaching.

  Post had caught his own glimpse of the jets over Siberia and Alaska, but the next time they showed up was above Japan, toward the end of the Second World War. American B-29 bombers had been specially designed to fly above thirty thousand feet, so they could evade enemy fighter planes while preserving their bombing accuracy. But, bizarrely, when they arrived over Japan their targeting went completely awry. The bombers should have been traveling at 340 miles per hour, but their instruments claimed they had a ground speed of 480. At that speed there was no way they could zero in on targets five miles below. The commanders were more inclined to blame the pilots for incompetence than to credit their tales of hurricane-strength winds above the clouds, but doubts were beginning to set in.

  Still, nobody knew that these rivers of air could be anything more than a weird local effect until, on a hunch, the Japanese military released thousands of booby-trapped balloons in early 1945. The balloons were equipped with an ingenious device to keep them floating in the jet stream: If they dropped too low, a pressure sensor would detonate a charge and a small bag of ballast would be jettisoned into the Pacific. The military had no idea how far the balloons would get, but one thousand of them made it all the way to the west coast of America. By hitching a ride on their invisible river, they had traveled six thousand miles in only four days.

  Many were shot down. Some were captured. "Japan attacks U.S. mainland with bomber balloons" was a headline guaranteed to cause panic, and the U.S. military was determined to keep the story out of the press. Then, on May 5, 1945, in Bligh, Oregon, a group of Sunday school children went out to the woods for a picnic. It was a beautiful summer day, and the kids suspected nothing as they raced over to the strange device that lay in a clearing. Nobody knows who touched it first, but their bones were embedded, along with shrapnel, into the surrounding trees. Five children and their teacher were killed. They were the only fatalities on mainland America during the entire war.

  But while people in the northern hemisphere were discovering the power of the jet streams, nobody yet suspected that they might also occur in the south. Commercial flight was just beginning, and few planes could fly high enough to notice the change in wind. One of those few was a British Lancaster airliner called Stardust, which had been designed to fly high over the Andes in case it needed to avoid the storms and clouds that often hugged the mountain peaks. On August 2, 1947, Stardust took off on a straightforward flight from Buenos Aires, Argentina, bound for Santiago, Chile. This would involve a simple hop over Mount Tupangato, one of the highest peaks in the Andes. According to the weather reports, visibility would be poor, so as they approached the mountain the Stardust's pilot radioed his intention to climb up to 24,000 feet. Radio contact continued as normal; the pilot reported that he had crossed the mountain and was about to descend into Santiago airport. Then, without warning, the plane vanished.

  After fifty baffling years, investigators have finally worked out what happened to the Stardust. It wasn't alien abduction, a South American "Bermuda Triangle," or any of the other bizarre theories that had been advanced in the intervening time. Instead, the unfortunate plane had encountered the southern jet stream. As Stardust rose to 24,000 feet, it suddenly encountered a fierce headwind blowing her backward at more than one hundred miles per hour. The problem was that the pilot didn't know this. He had no radar to tell him that his ground speed had just dropped by nearly half, nor were there any radio stations tracking his position from the cloud-covered, uninhabited ground below.

  All he could do was calculate his position according to the speeds the instruments gave him. So when he thought he had arrived near Santiago, he had not yet cleared the mountain. When the plane crashed into the eastern face of Mount Tupangato, the three crew members and six passengers on board were killed instantly. Seconds later, an avalanche triggered by the impact covered the plane in a blanket of snow, from where it gradually sank into the heart of the glacier and made its frigid way down to the valley floor.

  If the glacier hadn't spat out the remains of the plane some fifty years later, nobody would have known that the jet
stream had claimed more vic tims. And yet, the streams themselves are far from malevolent. Now that we understand them and can monitor where they form, they are even living up to Wiley Post's dream of using their power. A boost from the powerful jet stream that blows east from North America to Europe explains why transatlantic flights are nearly an hour faster going east than going west. And in 1999 a balloon, the Brietling Orbiter, used the jet streams to hitch a nonstop ride around the world.

  But the jet streams are much more important than this—they are the final step in making our planet habitable. For they act as guides for the rolling ball bearings of Ferrel's circular storms.

  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.

  PART 2

  SHELTERING SKY

  CHAPTER 5

  THE HOLE STORY

  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 experime
nts 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.