Foundations of the Eart: Global Ecological Change and the Book of Job

There are places where the winds have names.1 Zephyr, shown in the illustration opening this chapter, was the Greek god of the west wind, the gentle wind that signaled the coming of spring. There was a panoply of Greek and Roman wind gods, each with a different direction and a different personality. There are other, less divine, named winds as well. A sirocco is a scorching, dry, dust-filled November wind that blows out of the Sahara with speeds as high as one hundred kilometers per hour.² A chinook is a dry wind that has been warmed by compression as wind moves downslope over the Front Range of the Rocky Mountains and onto the Canadian plains and the U.S. Great Plains. Chinooks can raise winter temperatures from well below freezing to warm enough to melt as much as a foot of snow in a day. A föhn is a similar wind that blows downslope from the Alps.³ The Fremantle Doctor is a cool afternoon wind off of the Indian Ocean that provides relief from the blazing hot summers of Perth, Western Australia.⁴ The monsoon is a complete reversal in the pattern of winds that brings the rainy season to areas near the equator and even at higher latitudes.⁵ A calima is a dry summer wind from the southeast that blows Saharan dust across the Canary Islands. Ultimately, transported Saharan dust fertilizes the Amazon with phosphate, an often limiting plant nutrient.⁶ Nor’easters are fierce winter storms that batter beaches and houses along the Atlantic coast of Canada and the upper U.S. Atlantic coast.

These winds gain their names from their regularities—the similarity of their patterns and when they reoccur generates a seeming familiarity. We know them by their look, smell, and feel; by the timing of their arrivals and departures; by the changes they wreak. The processes that cause the regular features of winds arise from underlying fundamental physics of the way heat is distributed.

How much can a chinook change the local temperature? The most extreme twenty-four-hour temperature difference recorded for the United States (a change of 57°C) was produced by a chinook wind in Loma, Montana.7 On January 23, 1943, a chinook in Spearfish, South Dakota, generated a 27°C change in temperature in two minutes, a record that still stands.⁸ Föhns, the chinooks’ European cousins, help warm central Europe and provide it with a milder climate than would otherwise be expected there.

Hurricanes, typhoons, and tropical cyclones are large, remarkably powerful, organized tropical storms. These storms are called hurricanes when they occur in the Atlantic and Eastern Pacific,9 typhoons in the northwestern Pacific,¹⁰ severe tropical cyclones in the southwestern Pacific Ocean and southeastern Indian Ocean,¹¹ and severe cyclonic storms in the northern Indian Ocean. In all cases, they feature maximum sustained winds greater than thirty-three meters per second (roughly seventy-four miles per hour), although the U.S. definition of a maximum sustained wind differs from that used by most other countries.¹² For convenience, they will be referred to as hurricanes in this section unless the more geographically specified term is appropriate.

“Hurricane” derives from the Carib/Taino/Arawak storm god Juracán, itself from the Mayan god Hunrakan, a creator storm god who blew his breath across the chaotic waters and created dry land. The meteorologist and the British East India Company’s president of the Marine Courts of Inquiry at Calcutta, Henry Piddington, coined the word “cyclone” in 1844, with, “I am not altogether averse to new names…we might perhaps for this last class, of circular or highly curved winds, adopt the term ‘cyclone’ from the Greek Κυκλως (which signifies amongst other things the coil of a snake).”¹³ Snaky etymology is found in another name for these storms, typhoon, which may originate with the Greek monster, Typhon,¹⁴ a horrifically large creature with the lower half of its body as a gigantic serpentine coil, a human upper half, and serpents affixed as fingers on each hand.¹⁵

The fierceness and devastation of tropical cyclones, hurricanes, and typhoons are etched on the memories of their victims and sometimes on human history. Their impact inspires personification. Kamikaze (Japanese for “divine wind”) refers to two major typhoons in 1274 and 1281, which destroyed the Mongol Kublai Khan’s invasion fleets intent on the subjugation of Japan.¹⁶ Kamikaze subsequently designated the Japanese suicide-attack airplanes used over six centuries later in World War II. For several centuries in the West Indies, hurricanes were named according to the saint’s day when it arrived. Thus a particular hurricane could have different name when it arrived in another location on a different day. Terrible hurricanes striking the United States often were designated by place and year: the Galveston Hurricane of 1900 or the Great New England Hurricane of 1938.

The first modern meteorologist to name tropical cyclones was the eccentric Clement Lindley Wragge, who in the 1880s and 1890s worked as a government meteorologist for Queensland in Brisbane.17 Wragge connected a system of weather stations by telegraph (including an undersea cable to New Caledonia in 1893), which allowed him to study and track typhoons. He took a perverse delight in naming Australian typhoons after politicians as well as applying names from Polynesian mythology and European history.

During World War II meteorologists in the U.S. armed forces in the western Pacific took up the informal tradition of naming tropical storms after their wives and girlfriends. An early feminine naming of tropical cyclones appears in George R. Stewart’s 1941 novel Storm, which featured a Pacific storm named Maria as its principal character. Storm inspired Alan Jay Lerner and Frederick Loewe to write the song “They Call the Wind Maria” for their 1951 musical Paint Your Wagon. In 1953, Storm and the previous informal wartime convention provided the impetus for officially using women’s names for Atlantic tropical cyclones. The practice ended in the late 1970s, in no small part because the naming of agents of death and destruction after women seemed inappropriate to the changing times. Both male and female names are now used alternately.

A typical hurricane will have a nearly circular “eye” typically thirty-five to fifty kilometers in diameter located near the center of the storm. The eye is an open column of relatively calm, warm air. This core of warm air is what most clearly separates tropical cyclones from other spiral storms.¹⁸ The eye of the storm is surrounded by an eyewall, which contains the strongest winds in the system. Winds in the eyewall spiral upward.

The condensation of water in the rising eyewall vortex produces remarkable volumes of rain. The rising and spiraling eyewall air vents out the top of the eyewall, roughly eighteen kilometers high, and forms a layer of high-altitude cirrus clouds.19 Some of this air also moves downward into the cyclone’s eye and makes it more cloud free. As the winds spiral away from the top of the eye, they deflect to the right in a clockwise direction. At the frigid, high-altitude temperatures of around –70°C (–94°F), the air cools, becomes denser, and drops back to the ocean surface. Below the cirrus cloud cap, great curved arms of thunderstorms called rainbands spiral back into the hurricane’s center eye and are deflected to the right, in a counterclockwise rotation. These are warmed and hydrated by warm ocean surface water, which provides the energy that fuels the hurricane system.

From a fixed location with a tropical cyclone passing overhead, the bands of torrential rainstorms build and diminish and then build again. Each rain is more intense and longer in duration than the previous one. If the eye happens to pass directly overhead, this increasingly violent progression of rainstorms reaches a crescendo, followed by the eerie calm of the eye’s passage. This is a dangerous time. If one leaves shelter into the calm to inspect the situation, the subsequent arrival of the other side of the eyewall can bring tragedy.²⁰

Hurricanes are well-defined and stable storm systems, at least as long as they are over warm ocean water. Their spiraling morphology is the consequence of several straightforward agents of motion—rising warm air, falling cold air, and air movement from high to low pressure. In addition to these, there are other forces that give hurricanes their striking organization. How do hurricanes function as working mechanisms?

It is initially difficult to think of a hurricane as a machine, probably because one tends to associate machines with solid physical devices—levers and screws for simple machines, cranes or V-6 gasoline engines for more complex ones. The mechanistic workings of fluid mechanisms become more apparent in vortices: whirlpools in liquid fluids and whirlwinds and tornados in gaseous fluids seem more tangible and visible. In the context of the present biblical text, God spoke to Job from a whirlwind (Job 38:1), and other parts of the Joban text identify whirlwinds as powerful forces not to be reckoned with by mortals. Regarding the fate of the unrighteous, “Terrors overtake them like a flood; in the night a whirlwind carries them off” (Job 27:20, NRSV). Regarding the power of God:

First, on a rotating Earth, the Coriolis force deflects the winds away from their straight-line, pressure-gradient-force-driven path of motion from high to low pressure. With a boundary at the equator, the inertia of moving air with respect to the planet’s rotating surface causes it to deflect to the right in the Northern Hemisphere or to the left in the Southern Hemisphere. Thus, air moving from the periphery toward the center of a tropical cyclone spirals counterclockwise toward the low-pressure center in the Northern Hemisphere and clockwise in the Southern Hemisphere. The Coriolis effect was noted early, if not first, in 1651 by Giovanni Battista Riccioli, a Jesuit priest and astronomer, and his assistant, fellow Jesuit Francesco Maria Grimaldi.21 Their research was an attempt at a correction in targeting cannonballs, which they reported to veer slightly to the right in the Northern Hemisphere.

Second, as the spiraling air approaches the eye of the hurricane, it speeds up from the conservation of angular momentum (mentioned in chapter 2 in regard to the formation of solar systems). As the spinning tightens around the hurricane’s eye, centrifugal force becomes increasingly important. Centrifugal force is the force that allows one to whirl while holding a pail of water without spilling it. This outward force relative to the center becomes larger as the velocity increases or as the radius of the spin decreases.²² As the hurricane’s winds spiral faster and tighter around the eye, the centrifugal force becomes increasingly larger and helps reinforce the boundary between the eye’s calm and the high-velocity winds of the eyewall.

1. Gases are heated and rise to reduce the pressure on the gas. This step is called isothermal expansion. In a conventional engine, this expansion might be the heat generated by exploding gasoline in an automobile engine; in a hurricane, it is the heat and moisture transferred to the inwardly spiraling wind from the warm ocean water.

2. Removed from the heat source, the air continues to rise. The air rises without the addition of heat from the outside but is warmed from the condensation of water, as was the case in the rising air generating a chinook. This adiabatic expansion (expansion without the addition of heat) occurs in the upward spiral in the wall around the hurricane’s eye and in the towering storms that form in the spiral arms of the hurricane.

3. At the top of the hurricane’s eye, the air spirals outward, and it is cooled in the cold upper atmosphere. The air drops with a nearly constant temperature; heat is radiated into space to balance the heat gained from compression. This approximates a condition called isothermal compression.

4. The cold air continues to fall and is compressed by adiabatic compression. This air would be on the outer part of the hurricane and would become warmer and wetter as it spirals back in toward the hurricane’s eye to complete the cycle.

This spiraling atmospheric machine is what the French scientist Nicolas Léonard Sadi Carnot described in 1824 as a heat engine.24 Carnot saw the motions of winds and ocean currents as products of heat engines: “To heat also are due the vast movements which take place on earth. It causes the agitations of the atmosphere, the ascension of clouds, the fall of rain and of meteors, the currents of water which channel the surface of the globe, and of which man has thus far employed but a small portion.”²⁵ The “fuel” for the hurricane heat engine comes from warm ocean water. The greater the difference in temperature between this warm surface and the cold of the upper atmosphere, the more work it can do. Hurricanes work to move air, and they are remarkably efficient and powerful engines for doing so. If it could be harnessed, the power generated by a typical Atlantic hurricane would light thirty billion standard hundred-watt light bulbs. A Pacific supertyphoon can generate ten times more power.²⁶

Hurricanes, once formed, are great atmospheric machines driven by heat and moisture. In general, they require ocean water temperatures of 26.5°C (80°F) to a depth of fifty meters, high humidity, and unstable air. Winds tend to disrupt cyclone formation, and they tend to form more than five degrees of latitude away from the equator. They also require a preexisting disturbed weather system. Hurricanes “feed” on the heat from warm ocean water. They strengthen over warmer waters and weaken over cooler ones. The increase in surface friction when they pass over land disrupts their organization.

Hurricanes can be tracked, particularly nowadays using satellites, but their future movements are simultaneously predictable and capricious. These are charismatic storms that, because of the danger they represent to life and property, light up the radio and television with weather reportage. News of the storms is essential for the survival of the people in their paths.

In the United States, ever since Dan Rather stood on the seawall at Galveston, Texas, in September 1962 to report live on the landfall of Hurricane Carla and was catapulted to national fame as a television journalist, it is hard to keep aspiring TV newscasters off the beach when a hurricane is coming in. Rather also introduced the first radar image of a hurricane to television audiences. On the radar screen, Hurricane Carla was about 640 kilometers wide as it approached the Texas coast. The public realization of the magnitude of Hurricane Carla (the largest hurricane by combination of intensity and size to make landfall in the United States) spurred an evacuation of 500,000 people from the Texas coast and may have saved thousands of lives.27 The Galveston Hurricane of 1900, which was thought to be of comparable intensity to Carla, killed at least 8,000 people and possibly as many as 12,000.²⁸

The Galveston Hurricane of 1900 was the deadliest natural catastrophe to befall the United States, but it pales in lethality to other storms. Of the six storms with mortalities of over 100,000 people, one of these, a typhoon that hit Japan in 1923, produced a death toll of 250,000, many of whom perished in a simultaneous earthquake and the resultant widespread fires.²⁹ Another typhoon landed in southern China in 1881 with an estimated loss of 300,000 lives. The rest and also the majority of the hundred-thousand-plus killer storms occurred in India or Bangladesh. The Bay of Bengal has high astronomical tides and a coastline that funnels water onto low, flat terrain. The worst storm of them all appears to have been the 1979 Bhola cyclone, which landed on the Ganges Delta region of Bangladesh and killed more than 300,000 people, with 200,000 recorded burials and another 50,000 to 100,000 people missing.³⁰ This was a moderate-strength cyclone, but it came in on a high tide and brought a twenty-foot storm surge along with it.

Hurricanes illustrate the forces involved with the intensity and directions of winds. The innermost part of a tropical cyclone has very low air pressure. The lowest pressure measured for an Atlantic tropical cyclone was generated by Hurricane Wilma, which in 2005 registered a central low pressure of 882 millibars, about 13 percent lower pressure than the average sea-level pressure and approximately equal to the atmospheric pressure at the height of 1,100 meters (close to the height of Denver, Colorado). The world record of 870 millibars is held by Typhon Tip (August 1979), a monster storm that at its peak was 2,220 kilometers wide. It eventually made landfall on October 19 in southern Japan.31

A hurricane is a very tangible example of a complex structure arising from fundamental interactions involving the pressure-gradient force, centrifugal force, Coriolis force, and friction. There are other structures organized by these forces at different scales in time and space. The rotation of winds around areas of low pressure demonstrates the same interactions. These interactions are also illustrated by the large-scale winds of the global circulation of the atmosphere. Likely, the earliest discovery of these large-scale circulations is the trade winds, which are found on either side of the Equator.

The Polynesian navigators knew of and understood how to use the trade winds in their colonization of the Pacific around 1000 CE.³² Their likely ancestors, the Lapita people of the western Pacific, were making significant voyages over two thousand years before, around 1350 BCE.³³ It should come as little surprise that the Polynesians, who designate directions on their island homes as “windward” or “leeward,” would intrinsically appreciate the trade winds as a part of the fabric of their lives.

Europeans, notably the Portuguese, utilized the trade winds starting in the early part of the fifteenth century to propel their rapid exploration of the oceans. The word “trade” describing these winds derives from a Middle Low German word, trade (trâ), meaning a track, a course, a path. The trades were sea paths made of winds. The importance of the trade winds to British merchant fleets later inspired the alternate meaning of trade as “commerce.” These beneficent winds blazed an ocean path to exploration, discovery (see chapter 8), and commerce.

It is one thing to know that these winds are there; it is another, deeper thing to know their cause. The story of this understanding is a mixture of lost discovery and incorrect attribution, of good science lost in the scientific literature, of opportunity lost.

Understanding the cause of the trade winds attracted the attention of the renowned British astronomer Edmond Halley, who developed the theory, now known to be incorrect, that the tropics followed the daily cycle of the Sun’s heating, which moved from east to west, creating a flow of denser (cooler) air toward the west-moving area of maximal heating.34 In his conjecture, the winds chase the heat of the day as it lifts air and races ever westward around the planet.

Forty-nine years later in 1735, George Hadley explained that air would be heated at the Equator and would rise to be replaced by air drawn in from areas to the north and south, creating a flow of air from both sides toward the equator.³⁵ Further,

air, as it moves from the Tropics towards the Equator, having a less Velocity than the Parts of the Earth it arrived at, will have a relative Motion contrary to that of the diurnal Motion of the Earth in those Parts, which being combined with the Motion towards the Equator, a N.E. wind be produced on this Side of the Equator, and S.E. on the other.³⁶

Sadly, Coriolis’s essay providing the mathematics and physics behind the Coriolis force, the component that generated Hadley’s eastward component for the trade winds, was not to be published until a full century later.³⁷ Hadley’s insightful work required a deeper understanding that simply was not available. He was brilliant but before his time.

Hadley’s work quickly became scientific “old news” and was lost almost as soon as it was published. George Hadley was a relative scientific unknown who was often confused with his more famous brother John Hadley, the inventor of the octant (a device for calculating an observer’s latitude from astronomical observations and a valuable navigation tool) and the developer of methods to make parabolic mirrors for reflecting telescopes.

Shortly before George Hadley’s paper, Halley’s earlier theory on the trade winds was published verbatim in a popular encyclopedia.38 By dark coincidence, Hadley’s and Halley’s names are similar enough that they were often confused, usually in Halley’s favor. Subsequent scientists developing theories similar to Hadley’s simply did not cite him. It would take a full century for George Hadley to be recognized for his explanation of the trade winds. Along the way, Hadley’s concept was reinvented without attribution. In 1793, it was discovered by John Dalton, the renowned English scientist best known for his contributions to physics, chemistry, and ultimately to the basis of modern atomic theory. Dalton eventually learned of the existence of Hadley’s much earlier work.

A modified version of Hadley’s concept was put forth, again without attribution, in 1837 by Heinrich W. Dove, a stereotypical Prussian meteorologist who ruled his field with a strong and sometimes dictatorial hand.³⁹ A letter posted on September 5, 1837, to Richard Taylor, the editor of the Philosophical Magazine read:

Notice Relative to the Theory of Winds

By John Dalton, D.C.L., F.R.S.

To Richard Taylor, Esq

Manchester, Sept 5th 1837

Dear Friend

I published a theory of the Trade Winds, &c, as Mr Dove has published,—it was forty-four years ago, as may be seen in my meteorology, 1793 and 1834.^[40] It was first published by G. Hadley, Esq, in 1735, as I afterwards learnt. It is astonishing to find how the true theory should have stood out so long.

—John Dalton

To the chagrin of Heinrich Dove, this letter, which was published in the Philosophical Magazine, also appeared soon thereafter in the Annalen der Physik.41 This ultimately produced a thorough, posthumous, and long-lasting association of George Hadley with meteorological explanations of the trade winds. In particular, the circulation in the tropics at the global scale is conceptualized as a paired system of recirculating winds called the Hadley cells.

The trade winds are deflected by the Coriolis force of the rotating Earth and come together toward the Equator. Where they converge, the air moves upward. The warm, moist tropical air cools as it rises, condenses to form tall convective clouds, and produces the copious rainfalls of the equatorial region. The air that has been transported upward to high altitudes (roughly fifteen kilometers) moves toward the poles, cools as it radiates its heat into space, and eventually sinks downward far from whence it originally rose. The sinking dry air heats from compression as it sinks and produces a zone of intense aridity near 30°N latitude and a mirrored dry zone at 30°S latitude. These are the latitudes of the Earth’s great deserts, the Sahara, the Namib, the Great Australian Desert, among others. These arid locations on land associated with sinking air have their analogues on the seas. These are areas of extensive calms called the Horse Latitudes by tall-ship sailors and the Subtropical High by meteorologists.

The rising air near the Equator creates a zone of low pressure; the zones of sinking air (at 30°N and S) become zones of high pressure. Thus there is a flow of air from high pressure to low. This creates the pressure-gradient force, which, coupled with the Coriolis force, drives the trade winds. These paired equator-centered circulation systems are the Hadley cells, posthumously named for George Hadley.

The zone of converging air from the trade winds located near the equator is called the doldrums. At sea, navigating the doldrums left sailing ships still in the water, sometimes for long and potentially deadly intervals as ship’s supplies were exhausted:

Africa straddles the Equator and lies to thirty-five degrees of latitude on either side. It shows clearly the effects of the Hadley circulation on land systems at long- and short-time scales. Africa has extensive deserts and arid zones in the horse latitudes and rain-green savannah and woodland transitioning to equatorial rain forests at the doldrums. This is the large-scale vegetation pattern one would expect for the Hadley circulation climate to develop over a longer period of time. The dominant effect of the Hadley circulation over Africa is the suppression of rainfall. With the exception of the high-rainfall regions in the convergence zones, Africa is a dry continent, with 70 percent of the continent receiving less than fifty centimeters of rain per year.43

The striking annual consequence of the Hadley circulation over Africa is the movement of the ITCZ and the movements of rains across the continent. Starting at the height of the Southern Hemisphere summer, the ITCZ is displaced to the south. This position of the ITCZ brings rain to Botswana, in the southern part of Africa. The southernmost part of the nation only gets a taste of the ITCZ rains before the rain belt begins to push northward. The rest of Botswana has rain and thundershowers for a longer time. Then the ITCZ moves further northward, and these regions wait for a dry season until the rain returns from its annual migration. The return takes six months in the wetter northern part of the country and eight or ten months in the dryer, more southern parts—the longer the wait, the longer the dry, and the less the annual rainfall. As the rain belt continues to migrate over Tanzania and Kenya, one of the last remaining great migratory herds of large mammal herbivores migrates across the Serengeti following the greening grass. In some intermediate locations, dry turns to wet as the ITCZ moves over, followed by dry again when it moves completely past, but then there is a second wet season when it passes over again on its return. Near the height of its journey north, it waters the Ethiopian Highlands and feeds the Blue Nile from June to September.

For example, in the tropical and subtropical South Pacific, the trade winds interact with ocean temperatures.46 In the normal circulation pattern, the trade winds push warm water toward the western equatorial Pacific, causing a “pool” of warm water to collect off of Indonesia and Australia. These warm seas heat the atmosphere, and this warmer humid air lifts to form thunderstorms and considerable precipitation. The lifted air, now high in the atmosphere, flows back to the east to close the circulation cycle by cooling and settling over the warm oceans.⁴⁷ The circulation moves heat from east to west across the Pacific. Its strength can be indexed by the difference in sea-level barometric pressure in Darwin, Australia, minus the pressure for Tahiti.⁴⁸

When these values are negative, abnormal conditions occur. The normally cold waters of the Humboldt Current off of Peru are replaced by warmer water. Without the ocean’s upwelling nutrient-rich cold waters from the Humboldt Current, the great Peruvian fishery collapses. Local fishermen call the event El Niño (“the little boy,” referring to the baby Jesus), because the event normally occurs around the Christmas season. The effect of an El Niño is felt in anomalous weather around the world: heavy rains in East Africa; drought in south-central Africa, southeastern Asia, and northern Australia; and bush fires and dry conditions in the eastern part of Australia and Tasmania, and elsewhere. The opposite condition, La Niña, is a cool phase of the circulation cycle in the Pacific. Africa becomes wetter, as do South Asia and Australia. The periodicities of these episodes are on the order of three to five years.

One of Walker’s major accomplishments was to identify through statistical analysis the periodic swings and sways of weather conditions in the equatorial Pacific.49 He identified three large-scale oscillations of air pressure.⁵⁰ The one just described, the Southern Oscillation with periodic El Niño and La Niña conditions, involves the Pacific Ocean, ultimately the Indian Ocean, and beyond. It was the strongest oscillation Walker identified. Of the two others, one was the North Atlantic Oscillation, with swings in the intensity of the difference in the low pressure normally associated with Iceland and the high pressure of the Azores.⁵¹ The other was the North Pacific Oscillation.⁵² Gilbert Walker’s fundamental idea was that climate variations operating on scales of years to decades arise from interactions between circulations of air and water in the Earth’s atmosphere and the oceans. These interactions also connect globally. Such oscillations, feedbacks, connections, and teleconnections will likely be an important topic of research for some time to come.

Air over the polar regions cools and then warms as it moves toward the Equator. This relatively warmer air rises and cools as it moves back toward the poles. This forms a pair of polar circulations with winds moving in the same directions as the trade winds. Systems of winds called the prevailing westerlies blow in the middle latitudes, between about 30° to about 60°N and S. Separated from the trade winds by the Horse Latitudes, the westerlies blow in the opposite direction of the trades—from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. The Horse Latitudes’ descending cold air forms an extended high-pressure region, the Subtropical High. This descending air moves as part of the Hadley cell toward the tropical low pressure of the ITCZ. It also moves toward the poles, where low pressure is generated by the warming and rising of the cold polar air. This poleward motion turns to the right because of the Coriolis force (and to the left in the Southern Hemisphere). A circulation cell arises from the transport of air poleward from the Horse Latitudes toward the low pressure of rising polar air. This is called the Ferrel cell, after William Ferrel, who theorized its existence in 1856.⁵³

Polar cells and the Hadley cells function in a relatively straightforward manner: air moves from a cooler high-pressure area toward a warmer low-pressure area, then rises and recirculates. The Ferrel cell is more complex. It is turns, like a cog between two large wheels, between the Hadley and polar cells. It transports heat toward the pole via its warm air. Its presence is manifested as the passages of great curling eddies of air—the comings and goings of highs and lows, of warm and cold fronts. It is a zone of mixing air, but its prevailing direction is southwesterly in the Northern Hemisphere. From the U.S. East Coast, one sees the effects of the westerlies in the movement of hurricanes, which march from the tropical Atlantic to the Caribbean, eastern seaboard, and Gulf coasts under the steering of the trade winds. They eventually curve back toward Europe when they move far enough north to be steered instead by the westerlies.

In the Southern Hemisphere, the westerlies traverse mostly open water. With little land to slow them down, they become stronger and more organized than their Northern Hemisphere mirror-twins. At around 40°S, the only land of any extent is Tasmania, New Zealand, and the southern tip of South America. The westerlies reach their maximum strength in a zone called the Roaring Forties, after their latitude. “Running the easting down” in the era of sail was the route of clipper ships sailing from England to Australia and New Zealand in the Roaring Forties, a wind expressway. Modern yacht racing uses a similar route. Usually the racers depart the European Atlantic, pick up the Roaring Forties south of the Cape of Good Hope, head west below Australia and New Zealand and swing past Cape Horn back to the European Atlantic coast. The current record time for this voyage is slightly longer than forty-five and one-half days.54

With the trade winds pushing waves and water to the east and the westerlies doing the same at higher latitudes to the west, the two work together to propel large water circulations in the great ocean basins. The Coriolis force operating on the moving waters also curves the movement and reinforces the direction of movement imparted by the winds. The results are large rotating ocean currents called gyres. There is also movement of water to relatively low-density warmer water from higher-density cold water, a direct analogue to the pressure-gradient force in winds. There are five major ocean gyres: the North Pacific and North Atlantic gyres rotating clockwise in the Northern Hemisphere and the Indian Ocean, South Pacific, and South Atlantic gyres rotating counterclockwise in the Southern Hemisphere. There are also smaller gyres, currents, and countercurrents working in this great clockwork of large ocean gyres.

Needless to say, the early ocean explorers were keenly interested in wind directions and sea currents, as they were a critical part of their voyages. The Portuguese, under the patronage of Prince Henry the Navigator (Infante Henry, duke of Viseu, 1394–1460), made prodigious advances in navigation, notably the technique they called volta do mar, or “turn of the sea.” The Portuguese were exploring the African coast in search of slaves and converts, which appeared to be interchangeable terms in the mind of Henry.55 In the process, the volta do mar technique was developed. Ships would work their way down the African coast, and to return, counterintuitively, they would sail west, moved by the trade winds and the currents of the North Atlantic Gyre, and then north to catch the westerlies for a fast return to Portugal. The further away from their Portuguese home, the further to the west they needed to go before circling north and then turning east to return. Otherwise, one would have to fight the winds of the trades to get back, a slow and potentially lethal strategy. In the process of working down the West African coast and swinging out on the volta do mar, the Portuguese discovered and colonized several remote Atlantic islands: Madeira, the Cape Verde Islands, and the Azores, which all became resupply ports for the return.

The Portuguese discovery of the Cape of Good Hope and the eventual route to the spice supply in India, southeastern Asia, and Indonesia involved a second volta do mar that involved heading east almost to Brazil before making the turn to run south of the Cape of Good Hope and heading for India.⁵⁶

The line between heroics and foolhardiness can be drawn very finely; some might say that in some cases there is no line at all. Some remarkable navigators bravely put their faith in the volta do mar to navigate vast stretches of unknown ocean. For example, Christopher Columbus on returning from his first voyage to the New World used a volta do mar to return to Europe. He sailed north to around 36°N latitude, caught the westerlies, and then headed east, landing in Lisbon on March 4, 1493.

The remarkable Andrés de Urdaneta served on the second complete circumnavigation of the world, the Loaisa expedition in 1525. He became a monk and then sailed again in 1564 on the orders of Philip II of Spain for the conquest and colonization of the Philippines. From there he was sent to find how to get from the Philippines to Mexico across the Pacific.57 He employed a volta do mar, sailing as far north as Japan (38°N) to find the westerlies, pioneering a route from Manila to Acapulco. He arrived on October 8, 1564, with a nearly dead crew.

His discovery, the Urdaneta route, was sailed by the Manila Galleons, two ships that brought Ming porcelain, furniture, silk, carved ivory, and lacquerware from Manila to Acapulco to trade for Mexican silver.⁵⁸ The galleons were incredible sailing ships capable of carrying two thousand tons of cargo and one thousand passengers. The trade route lasted until 1815. Some of the remarkable merchandise from the Manila Galleons is on display in the Museo Histórico de Acapulco in Acapulco, Mexico.

The ocean gyres and the eddies, currents, and countercurrents, coupled with the trade winds and prevailing westerlies, gave explorers in the age of sailing ships and exploration the ability to determine efficient routes over the open ocean. The ships initially used by the Portuguese and Spanish explorers were caravels, relatively small ships with lateen sails, which allowed the ships to sail close to the wind and advance (beat) against a headwind using a zig-zag course.⁵⁹ Clearly, for a voyage into unknown territory, a ship with the ability to return regardless of wind direction is a wise design choice. For example, Columbus’s first exploration to the New World sailed on three vessels: The largest, the Santa Maria, was a carrack with both lateen and square-rigged sails; the other two, the Pinta and the Santa Clara (nicknamed the Niña), were lateen-rigged caravels. Once the sea routes were established, fully rigged ships with three or more square-rigged masts plied the ship routes.⁶⁰ The fully rigged ships were fast with fair winds but could not sail close to the wind.

There is one additional aspect of the winds and ocean circulations to discuss. Some of the large-scale ocean circulation is driven by differences in the density of sea water. Very cold and very salty seawater, which is produced only in a small part of the ocean surface, sinks and flows as deep ocean currents to return eventually to the surface at a faraway location. The resulting circulation is called the thermohaline (temperature-salty) circulation.⁶¹ One way to make really cold and salty sea water requires polar conditions and strong winds both to cool the water further and concentrate the salt by evaporation. These conditions occur in the North Atlantic at two regions, the Nordic Sea and the Labrador Sea. This sinking water forms what is called the North Atlantic Deep Water, which flows south.

These flows of dense water are steered by the topography of the ocean basins. The flows of cold, salty waters eventually connect with other surface ocean currents to form a “mechanically-driven fluid engine capable of transporting vast quantities of heat and freshwater.”62 The joining of the deeper circulation with the surface circulation of water forms a connected circulation of water referred to as the ocean conveyor belt.⁶³ One loop on this conveyor belt starts with the North Atlantic Deep Water forming in the seas to the south and east of Greenland: the cold, salty, deep water sinks and flows south under the surface warm current the Gulf Stream and then through the basin of the Antarctic Ocean. There one branch of the North Atlantic Deep Water goes into the Indian Ocean and upwells as it becomes fresher and less salty by mixing with the waters of the Indian Ocean. This water is eventually transported into the South Atlantic up the western side of Africa, across the Equator to the west along the Equatorial Current; mixes with the waters forming the Gulf Stream; then moves northward to the seas off of Greenland from whence it came to cool and sink to repeat the cycle. The other loop of the conveyor belt involves the eventual merging of the Antarctic Bottom Water with the second branch of the North Atlantic Deep Water, which eventually mixes and upwells in the Pacific.

The ocean conveyor belt interchanges the waters of the oceans and transports considerable heat toward the polar regions. For example, in the North Atlantic, the Gulf Stream moves warmer water to higher latitudes in the North Atlantic and thus gives Europe a milder climate than one might expect. Palm trees grow in Inverewe Garden along the Highland coast in Scotland at almost 58°N latitude; this is around the same latitude as the frigid Labrador Sea that forms the North Atlantic Deep Water. In the past, events have changed the movement of these ocean currents, with fierce consequences to climatic patterns.

One significant case involves the Gulf Stream and the onset of over a millennium of fiercely cold climate conditions across Europe and elsewhere, called the Younger Dryas.64 At the end of the last glacial, about 14,000 years ago, the continental glaciers began to melt. From the fossil remains of plant parts, notably plant pollen preserved in lake sediments (see chapters 3 and 8), conditions worldwide were warming—fragmented tropical forests began to coalesce; boreal tree lines were moving north; and a cold, dry biome (the tundra-steppe) began to retreat.

Then, apparently quite rapidly, Europe went into a deep freeze. Vegetation resembling the vegetation of full glacial conditions returned, and glaciers began to build and expand. The event was called the Younger Dryas, after the tundra and high alpine plant, Dryas octopetala, a white wildflower indicative of cold conditions and whose pollen is extremely common in lake sediments formed during this time. The event occurred between 12,800 and 11,500 years ago. The Younger Dryas ended abruptly, perhaps in as little as fifty years, and its onset may have been even more rapid.⁶⁵

The Younger Dryas was caused by a shutdown of the ocean conveyor belt by a glacial melting and large influx of freshwater released into the North Atlantic. This stopped the production of cold, salty seawater and, thus, the thermohaline circulation. The Gulf Stream flow slowed, and the transfer of massive amounts of heat to Northern Europe stopped. There are several theories as to what generated this influx of water: a gigantic flush of freshwater from an ice dam holding back a giant lake of melted glacier water finally giving way;⁶⁶ a change in climate patterns bringing more precipitation to the North Atlantic and shutting down the making of deep ocean water;⁶⁷ the eruption of the volcano that formed the Laacher See near Bonn, Germany;⁶⁸ or the impact of a carbonaceous chondritic asteroid or a comet into the North American glacier with heating and a tremendous freshwater release into the North Atlantic.⁶⁹

Regardless of the exact cause, the rapid climate change that seems to have occurred at both ends of the event is a cautionary tale. It appears that alteration of the ocean’s circulation and its movement of heat on Earth can have relatively rapid and highly consequential consequences.

The interconnected motions of wind and water about our planet are fueled by the difference in the heat absorbed by different parts of the Earth’s surface. Almost all of this energy is from the Sun (99.97 percent). Other sources of energy to the Earth’s surface are obviously small but include energy originating from geothermal heat and radioactive decay leaking to the Earth’s surface, tidal energy, and waste heat from fossil fuel consumption and nuclear reactors.⁷⁰ The amount of incoming solar energy that would fall on a surface perpendicular to the direction of light is around 1,370 watts per square meter (Wm^–2).⁷¹

However, most of the Earth’s surface is not perpendicular to the incoming solar radiation, and half of the Earth is dark at any time. Taking into account nighttime and slanted surface angles, the incoming solar radiation is 342 Wm^–2. For the Earth’s annual average temperature to remain constant, this incoming radiation must be balanced by a radiation transfer away from Earth. This balance is partially maintained by the 107 Wm^–2 that is reflected back into space by clouds, aerosol particles, and gases in the atmosphere.⁷² An additional 235 Wm^–2 is emitted by the surface and atmosphere as outgoing long-wave radiation.⁷³ This long-wave radiation is a function of the temperatures of the surface and atmosphere.

Without the atmospheric greenhouse gases, an Earth of around –19°C would produce enough outgoing radiation to balance the incoming solar radiation (minus reflection). The average surface temperature of Earth is some thirty-three degrees Celsius warmer, at about 14°C.⁷⁴ Greenhouse gases absorb outgoing long-wave radiation coming from the planetary surface and heat the atmosphere. This additional absorption of radiation gives us a warmer Earth.⁷⁵ This “natural greenhouse effect” is mostly due to two gases—water vapor and CO₂. Clouds also have a similar warming effect from capturing outgoing radiation, but clouds also “whiten” the Earth and reflect more of the incoming solar radiation, which yields a net cooling effect.

The tradeoff between the consequences of more clouds as a positive or negative effect on planetary warming is but one of many of the complexities of the Earth’s heat budget that we need to understand better. Without natural greenhouse warming, Earth would be a cold and foreboding planet with a frozen ocean.76

From the numerous articles in the news media and the pronouncements of sundry politicians and “talking heads,”, one might think scientists have only recently discovered the warming consequences of atmospheric greenhouse gases. That “greenhouse warming” has a history in science that goes back almost two hundred years may come as something of a surprise.

The initial discovery that gases in the atmosphere could capture radiation and increase temperatures was found in experimental chambers in an experiment conducted by Horace-Bénédict de Saussure, a Swiss aristocrat probably best known as the founder of mountain climbing as a sport. Based in part on this experiment, Joseph Fourier, a French polymath, theorized in an 1824 paper that the atmosphere, like a greenhouse, “lets through the sun’s rays but retains the dark rays from the ground.”⁷⁷ His “dark rays” would now be called infrared radiation.⁷⁸

An exploration of the effects of CO₂ in the atmosphere was famously developed in 1896 by the Swedish Nobel laureate Svante Arrhenius.⁷⁹ On the heels of a divorce, Arrhenius occupied his time through a dark Swedish winter by laboriously solving an estimated ten to one hundred thousand hand calculations on the greenhouse effect of different concentrations of CO₂ in the atmosphere. By the time he was done, he had determined the average change in temperature for every ten degrees of latitude and for four seasons using values of 0.67, 1.5, 2, 2.5, and 3 times the average CO₂ concentrations at the time.⁸⁰

In making these laborious computations, Arrhenius synthesized the experimental and observational physics of his day: measurements produced by Langley on the transmission of heat through the atmosphere, by de Bort on cloudiness for different latitudes, by Ångström on the absorption coefficients of water vapor and CO₂, and by Buchan on mean monthly temperature over the globe.81 Stephan’s law, which states that radiant emission varies as the fourth power of temperature, was used to calculate heat exchanges. Arrhenius estimated the absorption of the surface and of clouds (surface albedo and cloud albedo, respectively) as well as the effects of snow cover feeding back on the radiation budget by decreasing the surface albedo. For all this effort, several significant factors had to be omitted. Neither the horizontal transport of heat (by winds or ocean currents) nor the effects of changes in cloud cover were included in his computations.

Arrhenius’s work was part of a long and continuing evolution of our understanding of the climate of the planet. The results of his calculations resemble those derived modern general circulation models (GCMs) that currently are used in assessments of the planetary effects of increases in “greenhouse gases” in the atmosphere. As with the modern GCMs, the warming effects are greatest in the higher latitudes and in the winter. The magnitude of Arrhenius’s predictions of 5 to 6°C for doubled CO₂ is not out of line with recent GCM predictions, either.⁸² This agreement may be fortuitous in that, as noted above, Arrhenius’s calculations do not include important significant changes,⁸³ notably the horizontal advection of heat, clouds, and vegetation change (to be discussed in chapter 8). The Earth’s climate has feedback systems that complicate our evaluation of the consequences of our actions.

For example, increased greenhouse gases could increase the warming and thus cause snow and ice to melt in regions that are otherwise perennially white or to lengthen the ice-free season at other locations. This would make the surface land and water, which are darker than snow and ice, absorb more of the heat from the Sun and promote further warming.⁸⁴ This “ice-albedo feedback” could amplify an initial warming caused by increased greenhouse gases in the atmosphere. It is one of the many planetary feedbacks that this chapter has but introduced. Certainly, we have begun to modify the composition of the atmosphere by introducing increased CO₂ from land clearing, cement production, and fossil fuel combustion as well as by producing and releasing other greenhouse gasses.