Chris Maser

Long before humans harnessed the wind, dust circumnavigated the globe in an ocean of air. The wind's variable strength—which can be thought of as circulating energy—determines both the amount and size of the airborne dust.1 Moreover, Asian dust is a regular component of the troposphere over the eastern Pacific and western North America, and is common across North America, at least during spring.2 (The troposphere is the lowest major layer of the atmosphere, extending to a height of 6-10 miles, 10-16 kilometers, from the Earth's surface.) Although the same is true for such Pacific Islands as Midway, Mauna Loa, and Guam, as well as Shemya Island, which is one of the Aleutian Islands in Alaska, occasional synoptic events bring Asian emissions to Guam from either East Asia or Southeast Asia (e.g., Indonesia), generally during late summer and autumn.3

In South America, on the other hand, most of the dust in Antarctic ice cores originates from the glacial outwash in Patagonia. (Glacial outwash refers to the sediments deposited by streams that are flowing away from glaciers.) Sedimentary evidence suggests that proglacial lakes provided an on/off switch for the flux of dust to Antarctica during the last glacial period. Whereas peaks in the amount of dust coincide with periods when the rivers of glacial meltwater (water that comes directly from melting snow or ice) deposited sediment directly onto easily mobilized outwash plains, but no such peaks occurred when glacial meltwater went directly into proglacial lakes. (A proglacial lake is a lake formed either by the damming action of a moraine or ice during the retreat of a melting glacier. A moraine, in turn, is any glacially formed accumulation of loose glacial debris, such as soil and rock, that occurs in currently glaciated and formerly glaciated regions.)4


"Glacial till" is the unsorted accumulation of rocky materials carried by glaciers as they moved down the mountains, including finely ground rock called "glacial powder," which is essentially dust. The glacial till in the photograph is left by the melting glacier on Mount Hood, Oregon, as well as the "glacial outwash," which is the glacial material being carried into the valley by water from the melting ice.

Traveling dust initiates an incredible range of effects as it goes from place to place. For example, the wind-scoured, nearly barren southern Sahara Desert of North Africa feeds the Amazonian jungle of South America with mineral-coated dust from the Bodélé Depression, which is the largest source of dust in the world. During the Northern-hemisphere winter, winds routinely blow across this part of North Africa, where they pick up 700,000 tons (635 metric tons) of dust on an average day and sweep much of it across the Atlantic. Approximately twenty million tons of this mineral-rich dust fall on the Amazon rainforest and enrich its otherwise nutrient-poor soils. The Bodélé Depression accounts for only 0.2 percent of the entire Saharan Desert and is only 0.05 percent of the size of the Amazon itself.5

On the other hand, two intense dust storms generated over the Gobi desert by springtime low-pressure systems in 1998 crossed the Pacific Ocean in five days to reach the mountain ranges between British Columbia, Canada, and California in the United States. Once there, the dust had a severe impact on visibility in areas where it concentrated and simultaneously reduced the direct solar radiation, but doubled the diffuse radiation. Yet in East Asia, the blowing dust increased the albedo effect over the ocean on a cloudless day because the dust was lighter than the ocean's surface and thus reflected the electromagnetic radiation back into space, thereby preventing it from being absorbed by the dark water.6 ("Albedo effect" is the electromagnetic radiation reflected back into space by a light surface, such as snow; albedo is Late Latin for whiteness, from the Latin albus, white.)

The dark surface of the ocean absorbs the sun's radiation, thereby increasing in temperature, which causes the water to expand and thus occupy more space.

Contrariwise, decreases in the amount of atmospheric dust over the past 30 years have contributed more to the warming of the Tropical North Atlantic Ocean than has climate change per se. Nevertheless, changes in the surface temperature are sensitive to regional changes in stratospheric volcanic and tropospheric mineral aerosols.7 (The stratosphere is the atmospheric layer immediately above the aforementioned troposphere and contains most of the Earth's ozone.)

Mineral-laden dust also contributes to the concentrations of dissolved iron in the marine ecosystem.8 In addition, dust carries live bacteria to the glacial ice of the East Rongbuk Glacier at an elevation of 21,385 feet (6,518 meters) above sea level on Mt Qomolangma (Mt. Everest) in the Himalayas. The bacterial diversity and concentrations depend on the amount of airborne dust. Four general periods of bacterial activity occurred between 950 and 1963 AD, each corresponding to a abundance of dust.9

The Himalayas from 12,000 feet (3,658 meters) on Phulung Ghyang, Newakot, Nepal, in May 1967.

The concentration of bacteria that can be cultured from an ice core taken on East Rongbuk Glacier is highest in the premonsoon season, next highest during the monsoon, lowest during the postmonsoon season and third highest during winter. The high concentration of bacteria deposited during the premonsoon season is attributable to the transportation of continental dust stirred up by the frequent dust storms during spring. A similar situation occurs in Tibetan glaciers owing to dust that originates in Northwest China. The culterable bacteria deposited in the glacier during the monsoon season are more diverse than those deposited at other times, possibly due to their derivation from both marine air masses and local or regional continental sources, whereas the bacteria deposited during the other seasons are transported only by the westerly winds.10

Moreover, primary biological aerosol particles influence atmospheric chemistry and vice versa through micro-biological and chemical properties and processes.11 Primary biological aerosol particles that include pollen, plant and fungal spores, plant debris, epithelial cells, bacteria, algae, protozoa, and viruses, all of which are a ubiquitous component of the atmospheric aerosols, and are most probably present in all size ranges. Besides their effects on air hygiene and health, biological particles play an important role in cloud physics. Some bacteria, for example, are able to accumulate water and act as ice nuclei.12

Primary biological aerosols represent a significant fraction of air particulate matter and hence affect the microstructure and water uptake of the aerial particles. Moreover, airborne microorganisms, namely fungal spores and bacteria, can transform chemical constituents of the atmosphere through their metabolic activity. Although bacteria are viable and digest portions of organic substances in cloud water, the viability and metabolic activity of airborne microorganisms depend strongly on such physical and chemical parameters as the atmospheric temperature, pressure, radiation, pH value, and concentrations of nutrients.13

Samples of fine, airborne particulate matter were collected along an altitude transect ranging from urban, rural, and high-alpine locations (Munich, Hohenpeissenberg, and Mt. Zugspitze) in the south of Germany, and were analyzed for their bacterial content by using mass fractions of DNA. Most of the bacterial sequences found in particulate aerosols were from Proteobacteria (which includes a wide range of gram-negative bacteria), while some were Actinobacteria (bacteria that inhabit plants and animals, including a few that are pathogenic) and Firmicutes (gram-positive bacteria). Ascomycota (sac fungi) and Basidiomycota (which include such fungi as mushrooms, puffballs, stinkhorns, and bracket fungi, along with many others) characterized the fungal sequences. These fungi are known to actively discharge spores into the atmosphere. The plant sequences could be attributed to green plants and moss spores, whereas a singular, unicellular organism, termed a protist, such as a protozoan, represented the animal DNA.14 A similar situation was found in high-elevation snow in the Alps (Mont. Blanc area in France) and the Andes (Nevado Illimani summit, Bolivia), as well as from Antarctic aerosol (French station Dumont d'Urville), and a maritime Antarctic soil (King George Island, South Shetlands, Uruguay Station Artigas), which lacked plant nutrients but had a large amount of dissolved oxygen throughout.15

In addition to dust, the movement of air also causes water to evaporate, ascend to ride the wind near and far, and be disseminated throughout various parts of the world as precipitation. Without wind, there would be no winter storms carrying moisture-laden clouds to blanket the high elevations with snow, which is the seasonal storage of water for the lower elevations. Moreover, without wind, there would be no monsoons to water the crops of Asia, as history attests.

If you are wondering where the Asian Monsoons may have originated, we need to go back to the collision between the Indian and Eurasian continents, which began 45 to 55 million years ago. Subsequently, the features that dominate the architecture of Himalayan Mountains developed 23 million years ago along what is today the Nepalese-Tibetan border. Erosion of the Himalayas intensified as the increasing uplift reached a peak around 15 million years ago, although it remained high until 10.5 million years ago and then slowed gradually until 3.5 million years ago. However, it began to increase once again in the Late Pliocene (5.332 million to 1.806 million years ago) and Pleistocene (1.8 million to 10,000 years before the present) epochs. Records of geological weathering from the South China Sea, Bay of Bengal, and the Arabian Sea permit the reconstruction of the Asian monsoon climate back 23 million years, during which time there is evidence of a dynamic coupling between the climate and both the building of and erosion of the Himalayas.16

Snow accumulating in the Himalayas in late May 1967, as the monsoon season got under way.

Within historical times, however, Chinese dynasties, such as the Tang (618-907) and the Northern Song (960-1127), enjoyed increased yields of rice during periods when the monsoons were strong. In fact the yield of rice during the first several decades of the Northern Song Dynasty allowed the human population to increase from 60 million to as many as 120 million. But periods of weak monsoons ultimately spelled the demise of dynasties.

The Tang Dynasty, for example, was established in 618 A.D., and is still determined to be a pinnacle of Chinese civilization, a kind of golden age from its inception until the ninth century, when the dynasty began to lose its grip. The Tang was dealt a deathblow in 873 A.D., when a growing drought turned horrific, and widespread famine took a heavy toll on both people and livestock. Henceforth, until its demise in 907 A.D, the Tang Dynasty was plagued by civil unrest.

Weak monsoon seasons, when rains from the Indian Ocean no longer reached much of central and northern China, coincided with droughts and the declines of the Tang, Yuan (1271-1368), and Ming (1368-1644) dynasties, the latter two characterized by continual popular unrest. Weak monsoons, with dramatically diminished rainfall, may also have helped trigger one of the most tumultuous eras in Chinese history, called the Five Dynasties and Ten Kingdoms period, during which time, five dynasties rose and fell within a few decades, and China fractured into several independent nation-states.

The strength of past Asian Monsoons was driven by the variability of natural influences—such as changes in solar cycles and global temperatures—until 1960, when anthropogenic activity appears to have superseded natural phenomena as the major driver of the monsoon seasons from the late twentieth century onward. In short, the Asian-Monsoon cycle has been disrupted at least in part by human-caused climate change.17

Besides monsoons, wind has spawned storms that have ravaged parts of the Earth and dramatically altered the stage on which the human drama is enacted. Hurricanes;18 cyclones;19 and tornadoes, which are Nature's most violent storms,20 have changed whole landscapes. Hot, dry winds have not only caused droughts throughout the centuries but also caused lightening storms and than fanned the flames of the resultant fires as they raced across grasslands and through forests.


Yet, somewhere in the long reach of time, the boat was invented, and men began to explore the watery world. At first, boats were powered by human energy. At length, however, the sail was invented to harness the wind's energy, and the age of sailors was born. From that day on, men have plied the seas, along with the wind-driven waves, in search of adventure and riches, in whatever form.

Although hot air or helium (which is lighter than air) has carried balloons aloft, it's the wind wherewith they have traveled while passengers have observed the land below. Other balloons carried instruments to send information to ground crews and thus helped to predict the behavior of weather patterns. Wind has also given many a child moments of joy as their kites tacked back and forth on the currents of air. As well, wind has long provided energy in the form of windmills through which water was drawn from below ground to the surface for human use. And today turbines are being used to gather, control, and translate the wind's kinetic energy into mechanical energy that people can put to work for their benefit.21 In addition, the power of wind-driven ocean waves is being harnessed by wave buoys and reconfigured for human use.22 With these few examples in mind, what do you think the world would be like without wind? On a smaller scale, air is compressed and used to drive nails into wood, alleviating the need to use a hammer. The foregoing is but a fraction of the ways in which humans have conceived to use air as a source of energy.


Although air currents carry life-giving oxygen, water, and life-sustaining dust to the Amazon, they also transport the "key of death"—a human legacy made visible. Toxins from such areas as the notoriously polluted air of Mexico City hitchhike on the wind across the Gulf of Mexico to the United States.23

And this is just Mexico. "Faster than mail traveling from Beijing to Seattle, air pollution and dust from China can speed across the Pacific Ocean and blanket broad swaths of North America."24 Although homegrown pollution is clearly the most potent, everyone's aerial garbage goes somewhere. For example, Asian dust crosses the Pacific to North American shores in 4 to 10 days, and carries with it such pollutants as arsenic, copper, lead, and zinc. In one case, at least, the heavy metals were traced to smelters in Manchuria because the dust passed over the smelters on its way to North America.25

Coming as no surprise, the quality of air decreases as the level of pollution increases, which causes chronic, adverse effects on lung development in city children from the ages of ten to eighteen. Moreover, diesel exhaust from buses, trucks, and farm equipment is a major component of air pollution throughout the world and is linked to lung cancer.26 In addition, chronic exposure to fine particulate aerial pollution clogs arteries and does lasting damage to blood vessels, although it may take relatively long time to develop.27 More specifically, it is a risk factor for mortality from cause-specific cardiovascular disease via mechanisms that likely include pulmonary and systemic inflammation, accelerated atherosclerosis, and altered cardiac autonomic function.28

An open-pit mine of soft coal near München, West Germany. The largest machine on Earth is used in this mine to extract the coal.

What is even more disturbing is a study from California documenting the fact that mothers who are exposed to chronic concentrations of the highest fine-particulate pollution gave birth to babies weighing 1.3 ounces (35.3 grams) less—about 1 percent on average—than babies whose mothers resided in communities with the cleanest air. These findings have important implications for infant health because of the ubiquitous exposure to fine particulate air pollution across the United States.29

If airborne particulate matter (often referred to as "aerosols") from such things as coal-fired power plants or forest fires is now added to the formula, they can alter the balance of energy affecting Earth by reflecting or absorbing energy from the sun. Whether this particulate matter exerts a net cooling or a net warming will depend on the type of particulate and its albedo effect, as well as that of the underlying surface.30

For example, heat from the sun reaching the Earth's surface has undergone decadal variations in Europe since the mid-twentieth century. These variations presumably result from changes in the amount of airborne particulate matter (such as fog, smoke, and various pollutants) and clouds. By analyzing multi-decadal data of horizontal visibility, it was found that the frequency of low-visibility due to fog, mist, and haze has declined in Europe over the past 30 years. This increased visibility was noted during all seasons and all distances of 0 and 5 miles (0 and 8 kilometers), and correlates with reduced emissions of sulphur dioxide, suggesting a significant improvement in air quality. Although it may seem counterintuitive with respect to the controversy over global warming, the improved air quality is calculated to account for an approximate average of 10 to 20 percent of the rise in daytime temperatures in western Europe and for about 50 percent of the rise in daytime temperatures in eastern Europe.31

Clean, healthy air to breathe is one of the primary components of the global commons and thus everyone's birthright.

Moreover, it seems that carbon dioxide is absorbed and stored more effectively by the world's vegetation under conditions of diffuse radiation from skies polluted with particle-scattering aerosols than under conditions of clean air and direct sunlight. Whereas this notion would seem to defy common sense because pollution decreased the overall amount of light falling on such vegetation as a tree, the particulates diffuse the radiation so that it actually illuminates more of the leaves, including those under the tree's outer canopy, thereby increasing photosynthetic efficiency. In fact, it is estimated that variations in the diffusion of particulate aerosols enhanced the land-carbon sink by approximately one-quarter between 1960 and 1999.32

Why the apparent paradox? That answer lies in the tiny particles and droplets of fog, sulphur dioxide, smoke, and other pollutants suspended in the air (aerosols) that scatter light and reduce ground-level visibility. However, while fog and the sulphur dioxide generated by coal-fired power plants are light and thus reflect the energy from the sun back into space, thereby cooling the atmosphere just above the ground, smoke particles from burning wood are dark (termed "black carbon") and absorbed the sun's energy, thus having just the opposite effect—something the that was not accounted for in the study.33

Black carbon, commonly termed "soot," is a black, powdery form of carbon produced when coal, wood, or oil is burned; it is the fine, particulate matter that rises up with the flames and smoke, and as such, is the dominant aerosol when it comes to absorbing the visible solar energy. Although human-caused sources of black carbon are distributed globally, they are concentrated predominantly in the tropics, where solar irradiance is highest. (Sunlight, in the broad sense, is the total spectrum of the electromagnetic energy given off by the sun. In turn, solar irradiance describes the relative amount of radiant energy emitted by the sun over all wavelengths that falls each second on 10.8 square feet [1 square meter] outside the Earth's atmosphere.)

Smoke from a forest fire in central Oregon.

Black carbon is often transported over long distances, and mixed with other aerosols along the way. The aerosol mix can form transcontinental plumes of atmospheric brown clouds that ascend vertically for 2 to 3 miles (3 to 5 kilometers). Emissions of black carbon, which are highly absorbent of the sun's energy, are the second only to those of carbon dioxide in their contribution to current global warming, in addition to which it has the capacity to form widespread atmospheric brown clouds in a mixture with other aerosols.34

To illustrate, smoke from over a hundred illicit fires set to clear forest or fields in Sumatra caused such a pall of smoke that officials closed schools and advise people to remain indoors. According to health officials, upper-respiratory ailments have increased sharply in Riau Province, as well as other parts of Sumatra due to the annual plague of forest and plantation fires, which pump huge clouds of smoke into the atmosphere. Although the practice of open-field burning was banned in Indonesia in 1999—after the widespread fires of 1997 and 1998 brought a choking haze that caused a public health crisis across some Southeast Asian nations—the ban has not been effective.35

Thus, brown clouds of smoke and soot from slash-and-burn agriculture and the combustion of fossil fuels blanket many regions of Asia. In doing so, these clouds enhanced lower-atmospheric solar heating by about 50 percent. Taking into account the vertically extended atmospheric clouds of pollution over the Indian Ocean and Asia, circulation models suggest the brown clouds themselves contribute as much to the regional warming of the lower atmosphere, as do increases in anthropogenic greenhouse gases. The air temperature between 1,650 feet (503 meters) and approximately 2 miles (3 kilometers) in altitude is 33 degrees Fahrenheit (1 degree Celsius) warmer than it would be without the pollution. Moreover, roughly 90 percent of the heating is attributable to the dark soot.36

Elsewhere, the interception of solar radiation by atmospheric brown clouds dims the sunlight at the Earth's surface, which has important implications for the hydrological cycle because, like circumstances in the Arctic, the deposition of black carbon darkens the surface of snow and ice, thereby contributing to its melting. For example, atmospheric warming due to black carbon at high elevations in the Himalayan region may be just as critical as carbon dioxide in melting the extant snowpacks and glaciers. In essence, the decreasing concentrations of light sulphate aerosols, along with increasing concentrations of black carbon in the mid- and high-latitude climate, have contributed substantially to the rapid warming of the Arctic and the consequent melting of the sea ice during the past three decades.37

For discussion's sake, let's suppose we achieve a world of lasting peace, a balanced and sustainable human population, food in abundance, gender and racial equality, and democratic governance, but we do not clean the air—then all is for naught. If we do everything except clean the air, we will still pollute the entire Earth from the blue arc of the heavens to the bottom of the deepest sea in every corner of the globe. Clean air is not only the very foundation of the global commons but also the absolute bottom line for human survival. Without clean air there eventually will be no difference in the way we commit suicide, either directly by nuclear war or indirectly through air pollution. Regardless of our choice, the consequence is the same. We will be the collective authors of our own demise—the "Greek tragedy" of modern society. But there are alternatives, and the choice is ours. To our children of all generations, we bequeath the consequences.


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  29. Jennifer D. Parker, Tracey J. Woodruff, Rupa Basu, and Kenneth C. Schoendorf. Air Pollution and Birth Weight Among Term Infants in California. Pediatrics, 115 (2005):121-128.

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  33. (1) Robert Vautard, Pascal Yiou, and Geert Jan van Oldenborgh. Decline of Fog, Mist and Haze in Europe Over the Past 30 Years. Nature Geoscience, 2 (2009):115-119; (2) Lorraine A. Remer. Smoke Above Clouds. Nature Geoscience, 2 (2009):167-168; and (3) Sid Perkins. Cleaner Air Means Warmer Europe. Science News, 175 (2009):9.

  34. The preceding two paragraphs are based on: V. Ramanathan and G. Carmichael. Global and Regional Climate Changes Due to Black Carbon. Nature Geoscience, 1 (2008)221-227.

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  36. Veerabhadran Ramanathan, Muvva V. Ramana, Gregory Roberts, and others. Warming Trends in Asia Amplified by Brown Cloud Solar Absorption. Nature, 448 (2007):575-578.

  37. (1) V. Ramanathan and G. Carmichael. Global and Regional Climate Changes Due to Black Carbon. Nature Geoscience, 1 (2008):221-227; (2) Noel Keenlyside. Clean Air Policy and Arctic Warming. Nature Geoscience, 2 (2009):243-244; and (3) Drew Shindell and Greg Faluvegi. Climate Response to Regional Radiative Forcing During the Twentieth Century. Nature Geoscience, 2 (2009):294-300.

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