The Army Air Corps needed meteorologists, and Lorenz was more than qualified with his Harvard degree, not to mention that he was still a passionate weather buff. He landed a plum posting as a military weather forecaster, a job that kept him out of combat. But the stakes were high. As the war deepened, the pressure to come up with accurate forecasts was fierce — other young men’s lives were on the line. Richardon’s equations were not yet in use, so accurate long-term forecasting was impossible. Meteorology was still an approximate science, based as much on intuition as it was on reading instruments or the look of clouds.
While Lorenz was second-guessing forecasts in the Army Air Corps, his fellow meteorologists were more interested in theory than pragmatics. The 1940s was a period when academic meterologists derided seat-of-the-pants forecasting. They much preferred the cleaner, more elegant theoretical side of meteorology, one in which potentially inaccurate forecasts didn’t put their reputations at risk. But Edward gained a lot of hard experience during the war, and by its finish, he knew weather as well as any individual could. Yet he also had unfinished mathematical business. There was something about those seemingly random sequences of daily highs and lows that he had recorded as a child, something lurking behind the numbers.
Fifteen years after the war ended, Lorenz was on the faculty at one of the world’s top research facilities, the Massachusetts Institute of Technology, and in 1962 he was appointed professor of meteorology. He had become a fixture at MIT with a reputation among his peers of being a little preoccupied and distant. That must have been a feat, given how many others in the faculty shared those characteristics. On top of which, he didn’t look the part of a scientist — he had a down-home, somewhat rural look, a weathered face and piercing gaze.
It was Lorenz who first thought of using a computer to mimic the fluid dynamics of the atmosphere. In the late 1950s, at a time when small computers, especially ones that occupied less than a room, were hard to come by, the Royal typewriter company had released the Royal McBee, a “compact computer” the size of a large desk. It had a keyboard to enter programs and commands and a printer to output results. It was like a Macintosh computer decades before there were any, though it cost around $16,000, the price of a modest, two-bedroom bungalow.
Lorenz persuaded MIT to buy him one. (The rest of the faculty was skeptical about the ability of such a small computer to contribute anything meaningful to hard science, but they were all fascinated by his new toy.) He programmed it to simulate world weather patterns. In his Royal McBee was a microcosm of the world, a planet within the planet. He modeled prevailing winds, high- and low-pressure systems, temperatures — and then he let the whole thing run on its own. Every once in a while, he’d check up on what was happening by looking at printouts that translated the changing weather on this small, ideal planet into wavy lines on a graph.
One day while running the weather program, he decided to skip ahead and pick up the sequence in mid-stride, as it were. To set the machine at the initial conditions, he typed in the number from an earlier printout and let the Royal McBee run the equations again while he went out to grab a cup of coffee. When he returned, he knew something was wrong. The lines on the new printout were diverging from the original, even though the number he’d typed in was identical to the first sequence. Well, almost identical. He had shortened the sequence by a mathematically infinitesimal amount; it couldn’t have produced such a divergence. Or could it? This is when Lorenz first intuited that weather sytems could be completely altered by the smallest change in the initial conditions. He rechecked his math and went to work. His revolutionary paper describing this process, delivered in 1972, was titled “Predictability: Does the Flap of a Butterfly’s Wings in Brazil Set Off a Tornado in Texas?”
It was a bombshell, exploding in the midst of the increasingly confident field of computer meteorology. The early chaos scientists called the butterfly effect “sensitive dependence on initial conditions” wherein a small perturbation at the beginning could cascade upward through the whole system, altering everything. A popular folk saying sums it up:
For want of a nail the shoe was lost;
For want of a shoe the horse was lost;
For want of a horse the knight was lost;
For want of a knight the battle was lost;
For want of a battle the kingdom was lost!
It became a David and Goliath conflict. Lorenz’s McBee had challenged the biggest computer in the world, the Cray supercomputer at the European Centre for Medium-Range Weather Forecasts in Reading, England, which used the von Neumann–Richardson algorithms. The stone in Lorenz’s slingshot was his simple simulation program that successfully, as it turned out, modeled the susceptibility of the Earth’s atmosphere to small initial changes.
If a supercomputer, with a far greater processing power than today’s forecasting supercomputers, was connected to weather sensors stationed on every square mile of the Earth’s surface and every square mile of the atmosphere and ocean depths, how accurately would it be able to predict the weather? According to Laplace’s theory of the omniscient intelligence, if the machine were perfect, then it would match reality in lockstep for millennia. But according to Lorenz, and even some of today’s meteorologists, it would fall behind reality in a relatively short period of time.
Jagadish Shukla, a climatologist at George Mason University, remarks that today’s forecasting computers can forecast the weather fairly accurately five days into the future. But there’s a limit, he insists, beyond which even the most powerful computer can venture: “We may not be able to get beyond day fifteen. [No] matter how many sensors you put in place, there will still be some errors in the initial conditions, and the models we use are not perfect . . . the limitations are not technological. They are the predictability of the system.” Perhaps we will never, ultimately, be able to forecast much beyond a fortnight. We can know the climate; we can predict the average temperature of the ocean for decades, even centuries ahead; but we cannot know what will happen in Brazil or eventually in Texas.
9
Apollo’s Chariot
The Seasons
The wolves are the first to sense it. For days now, they have been howling as they haunt the high Arctic darkness. It is late January in Grise Fiord, a settlement on the south shore of Ellesmere Island, and for three months the townsfolk have been locked in the icy talons of a pitch-black Arctic night. The wolf calls are a signal for everyone who lives here. The sun is coming. To the south, above the frozen ocean and low hills, an almost imperceptible daily brightening has begun. Week by week, this deep-red, noon-hour glow, a dawn rescinded daily, gets brighter and longer until it begins to rival the northern lights. Overhead, the Arctic stars have begun to dim.
At noon in the second week of February, something spectacular happens. The sun erupts above the horizon, For the first time in months, pure, unadulterated sunlight strikes skin, floods through windows and blinds eyes in an almost painful wound of light. This first sunshine, a day lasting only a few minutes, is spring in its purest form — raw and crystalline. The ice-hoary dwellings of Grise Fiord, like buildings long-submerged under the ocean and covered with coral encrustations, glow orange in the light, and every peak of the low hills surrounding the bay also glows with the same orange fire. Apollo’s flaming chariot has arrived, and burning deep inside his golden brazier is summer itself.
Of course Apollo doesn’t circle the Earth as the ancients contrived it. Instead, our planet circles Apollo; Apollo’s brazier, as it happens, is 93 million miles away from us. The reason our trek around the sun is also our journey through the seasons is due to something else: an asymmetry, a quirk. The ancient Greeks knew this. They wove it into their mythology in a story where Zeus, Apollo’s father, takes sides in the bizarre feud between two brothers, Atreus and Thyestes, who are contesting the kingship of Mycenae. Zeus favors Atreus over Thyestes, and when Thyestes captures a golden lamb, Zeus changes the cou
rse of the stars to express his displeasure. According to Roberto Calasso in his classic The Marriage of Cadmus and Harmony, this was nothing less than “an allusion to the tilting of the Earth’s axis.”
Migrating Climates
So it’s all in the tilt — spring, summer, fall and winter. As we rocket around the sun at 67,000 miles per hour, Earth’s 23.26° pitch creates the seasons. If we weren’t tipped relative to our orbital path (also known as the ecliptic plane), there would be no difference in the angle of sunlight hitting the Earth at different points of our orbit. There would be no midnight sun, no three-month polar nights, no solstices or equinoxes. Come to think about it, there would be no monsoons, hurricanes, typhoons or any great periodic winds either, because there wouldn’t be a thermal imbalance between the parts of our globe that the sun seasonally favored or abandoned.
In a perfect Euclidean universe, all the planets in our solar system would rotate with their north-south axes at right angles to the ecliptic plane. But they don’t. Since the birth of the solar system, some 4.6 billion years ago, the random impacts of large asteroids have skewed the rotational axes of every planet except one. So we’re not the only tippy planet in the solar system. Mars has a 25.19° tilt, Saturn tilts 26.73° and Neptune has a tilt of 28.32°. The crazy planets are Venus, almost upside down with a 177.3° tilt, and Uranus, pivoted sideways at 97.77°. Only Mercury is nearly vertical. In terms of extraterrestrial seasons, it would seem that Mars is our closest celestial relative. Its thin atmosphere may be 97 percent carbon dioxide, but Mars has seasons like our own, even if each one lasts little more than five months, due to the Martian year being 687 days long. (Curiously, the length of a Martian day is pretty much the same as ours.)
Here on Earth, the number of seasons is dictated by latitude. The tropics have only two seasons: wet and dry. The subtropics have three seasons: a wet one, a dry one and a cool or mild one that can sometimes overlap with the other two. The classic four seasons (well, six actually) are only experienced where the winters are cold and the summers hot. These regions, the temperate zones, stretch from about 35° latitude (the average limit of the subtropical regions) all the way to the Arctic Circle in the northern hemisphere and the Antarctic Circle in the southern hemisphere. Los Angeles, Buenos Aires, Capetown, Osaka and Sydney, for example, are tucked just within the subtropical zone, whereas London, New York, Berlin, Moscow, Montreal and Beijing are well inside the temperate zone.
The six seasons in the temperate zone are hibernal (winter), prevernal (late winter, early spring), vernal (spring), aestival (summer), serotinal (late summer) and autumn. I like these nuanced divisions, particularly prevernal and serotinal, because they capture something of the magic of seasonal transitions. In the northern temperate zones, the prevernal marks the time when the sap begins to run in late February and when, in early March, a few patches of snow remain on the northern slopes of hills, but the grass is green on the southern sides. Here in North America, the serotinal season is that marvelous time, in early September, when the monarch butterflies start to migrate, the lakes are still warm enough for swimming and the resorts are empty. As Helen Hunt Jackson writes in her poem “September,”
By all these lovely tokens
September days are here,
With summer’s best of weather
And autumn’s best of cheer.
Seasons are migrating climate zones. I don’t have to leave my house in Toronto to experience high Arctic or Amazon weather — they come to me. Here in the temperate zone, we import our climates, which arrive at crawling speed, roughly 0.7 miles per hour. Spring marches northward at about 17 miles a day, which means the first leaves open in London, England, 40 days later than in Barcelona, Spain. Leaf-opening in Winnipeg, Manitoba, lags behind Dallas, Texas, by a good 65 days. Summer recedes southward at the same speed as winter advances. Spring, summer, autumn and winter all recapitulate the ancient seasons of the Earth, and each is a temporal microcosm of the evolution of life itself.
When I was a child, it seemed life began on March 21, and even though it was often as cold as any day in February, there was an unmistakable intensity to the prevernal sunlight. Charles Dickens nailed it in Great Expectations when he wrote, “It was one of those March days when the sun shines hot and the wind blows cold: when it is summer in the light, and winter in the shade.” By March 21, the sap was running in the maple trees. Sometimes my parents would tap our sugar maple in the backyard. I remember cold mornings where a thin cap of ice had formed over the sap in the bucket, and I would carefully lift the thin disc of ice out of the bucket and nibble bits off the edges, letting them melt on my tongue. The faint sweetness was ambrosial.
Spring
“April is the cruelest month, breeding
Lilacs out of the dead land, mixing
Memory and desire, stirring
Dull roots with spring rain.”
T.S. Eliot, The Waste Land
When I was growing up, there was usually a period of dry weather in early April, an arid spell when the first high-pressure cells of the spring established themselves over the warming land. Grass fires would inevitably start and the fire department would come to extinguish the blazes. I can still see the long, canvas hoses winding like giant pythons through the burnt grass beside the pond.
High over the April landscape, in the upper levels of the troposphere, the northward swell of heat pushes up on the boundary between the troposphere and the stratosphere. The troposphere above the temperate zone, usually 11 miles high, gains an extra mile in height by midsummer. It’s as if the atmospheric infrastructure of the tropics expands its territory and, as the seasons migrate northward into the northern hemisphere, it seems anything with wings migrates with them. Sometimes insects will hitch a ride on a warm high-pressure system as they did in April 2012, when thousands of red admiral butterflies flooded southwestern Ontario, riding a northbound front up from Texas. One windy afternoon, my backyard was suddenly alive with these black, red and white butterflies.
Birds are famous migrators, often traveling thousands of miles, and their noisy return to their summer breeding grounds marks the official beginning of high spring. The famous swallows of San Juan Capistrano overwinter in Argentina and arrive in the southern Californian town almost always on the vernal equinox itself, March 21. Pretty punctual after a 6,000-mile flight.
The summery high-pressure cells that begin to preside over the northern temperate zones in May are not shared by the subtropics. There, the Earth’s tilt pushes the intertropical convergence zone — a rainy, global belt of low pressure caused by converging trade winds — northward. By June, the convergence zone shows up in the Caribbean as the rainy season. In the southern hemisphere, the opposite holds true, and the intertropical convergence zone slides south of the tropics in December.
By late spring in the temperate zones, the brand-new foliage exhales humidity and, in the sunlight after a summer shower, mists rise. The rainforest climate has moved in. Storms also ride north with the hot weather of late June, as thermals build cumulonimbus clouds in the humid air. The lilacs have finished blooming and, in my hometown, by the end of June the shallows at the edge of the pond are inky with tadpoles, some of which are already growing legs in a recapitulation of the evolution of fish to amphibians. The June peonies explode into blossom all at once. As Michael Cunningham wrote in The Hours, “What a thrill, what a shock, to be alive on a morning in June.”
Invincible Summer
“Summer afternoon — summer afternoon; to me those have always been the two most beautiful words in the English language.”
Henry James
Every winter I yearned for it, every spring I waited for it and every June, like a dependable miracle, it arrived. Summer was, and still is, the universal panacea, an antidote to adult worries, a time, wrote Ada Louise Huxtable, “when one sheds one’s tensions with one’s clothes, and the right kind of day is jeweled balm for the battered spirit. A few
of those days and you can become drunk with the belief that all’s right with the world.” Even the misery of poverty is somewhat remedied by summer, when “the living is easy.” For children especially, summer in the temperate zones is the gateway into an enchanted territory of imagination. As Lewis Carroll wrote in “Solitude,”
I’d give all the wealth that years have piled,
The slow result of Life’s decay,
To be once more a little child
For one bright summer day.
Of the four major seasons, none is as popular or as beloved as summer. It is then that we reestablish our sensual contract with nature. The beginning of summer in the northern hemisphere, the solstice on June 21, is not just six months away from the winter solstice in December, it is also 186 million miles away as the space crow flies. From solstice to solstice, the Earth has traveled half of its 584-million-mile journey around the sun.
In late spring and early summer, the jet stream migrates north along with the northward edge of the Ferrel cell, pushing the cooler polar air into the northern reaches of the temperate zone. With the arrival of summer, our senses are reawakened — the smell of roses, the hissing of lawn sprinklers, the sound of surf and children laughing, the wind in the leaves, the drone of lawnmowers. The intoxicating, silky swish of a summer breeze against bare skin. Ice cream and figs. The margin between indoors and outdoors is blurred, and the summer landscape turns into a vast, shared living room. With a pair of folding chairs and a picnic table, a backyard becomes a dining room and the local park becomes a stage for A Midsummer Night’s Dream. As Henry David Thoreau wrote in A Week on the Concord and Merrimack Rivers,
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