DOOMSDAY ASTEROIDS

"Asteroids Impacting The Planet"
MAY 2004: On January 13,2004 scientists and astronomers believed a newly discovered asteroid, over 100-feet in width and named the 2004 ASI, showed a 25% probability of global impact within 36 hours. The dilemma of alerting governmental leaders of this impact possibility was avoided, as later analysis indicated the asteroid would miss our planet. The fact that many asteroids may indeed hit the earth is problematic. Many of these roaming asteroids remain undetected as in the case of 2004 ASI, and when discovered, the planet may have only days to years of it's threat of global contact. In the case of 2004 ASI, if it were to have actually hit our planet, would have caused catastrophic results. The reality of this story is a simple one. Live every day as if it were your last, as it may very well be.

ASTEROIDS & EARTHQUAKES

Scenario: It is an evening in May 1999. The sky is clear, and there is no Moon. High in the north, just below the Big Dipper, a comet blazes. Found only a few weeks earlier by an amateur astronomer through a small telescope, it has been getting brighter until, tonight, it far outshines everything else in the sky. The comet breaks through the earth's atmosphere, destroying the ozone layer. Second's later, with a force of 100 million hydrogen bombs, slams into into the Pacific Ocean just off the coast of California. Virtually every rock within 5 miles of ground zero is instantly vaporized. The earth trembles as a force 12 earthquake topples any living creature standing. In less than one minute, a mighty shock wave gouges out a crater 100 miles wide and 25 miles deep. Mile high tsunamis rush upward from the point of impact and speed across the Pacific toward the American West Coast and Japan with tidal waves mile's in height, flooding the cities and destroying everything in their path.

Ground fires ignite and spread quickly around the world. As the World wide fires quicken and burn for months, fine dust thickens the in the earth's atmosphere. The sky becomes black as a darkroom, and for as long as six months there is no sunlight anywhere on the planet. Cooling rain falls, but the rains are poisoned with sulfuric acid. After more than a year of darkness, the skies begin to clear and the temperatures rise thus bringing the green house effect. A scene for Armageddon.

Our planet is no stranger to meteor impacts. For proof, just look at our own Moon. One of the Earth's oldest craters is in Sudbury, Ontario. The nickel mining city was the site of a impact around 1.9 billion years ago. Another crater, one of the largest discovered to date lies in the Yucatan Peninsula and is 65 million years old, some 150 miles wide. More than 3/4 of all life on the planet, including the dinosaurs, were extinguished with the impact.
 

                Near-Earth Asteroids

There are two groups of near Earth asteroids that deeply cross the Earth's orbit on an almost continuous basis. The first of these to be discovered were the Apollo asteroids, 1862 Apollo being detected by the German astronomer Karl Wilhelm Reinmuth in 1932 but lost shortly thereafter and not rediscovered until 1978. Apollo asteroids have semi major axes (a) that are greater than or equal to 1 AU and perihelion distances that are less than or equal to 1.017 AU; thus, they cross the Earth's orbit when near the perihelia of their orbits. For the other group of Earth crossing asteroids -- named Atens after 2062 Aten, which was discovered in 1976 by Eleanor F. Helin of the United States--a < 1.0 AU and Q 0.983 AU, the present perihelion distance of the Earth. These asteroids cross the Earth's orbit when near the aphelia of their orbits. (see also Index: Apollo group, Aten group)

By mid 1991 the number of known Aten, Apollo, and Amor asteroids were 11, 91, and 81, respectively. Most of these were discovered since 1970, when dedicated searches for this type of asteroid were begun: 25 were discovered during the 1970s, 80 during the 1980s, and 49 during the first 20 months of the 1990s. It is estimated that there are roughly 100 Atens, 700 Apollos, and 1,000 Amors that have diameters larger than about one kilometer. Because these asteroids travel in orbits that cross the Earth's orbit, close approaches to the Earth occur, as well as occasional collisions. For example, in January 1991, an Apollo asteroid with an estimated diameter of 10 meters passed by the Earth within less than half the distance to the Moon.

Asteroid, Inbound, 2044 AD

THE ASTEROID THEORY

The asteroid theory is widely accepted as the most probable explanation of the K-T iridium anomaly, but it does not appear to account for all the pale ontological data. An impact explosion of this kind would have ejected an enormous volume of terrestrial and asteroid material into the atmosphere, producing a cloud of dust and solid particles that would have encircled the Earth and blocked out sunlight for many months, possibly years. The loss of sunlight could have eliminated photosynthesis and resulted in the death of plants and the subsequent extinction of herbivores and their predators and scavengers.

The K-T mass extinctions, however, do not seem to be fully explained by this hypothesis. The stratigraphic record is most complete for extinction of marine life--foraminifera, ammonites, coccolithophores, and the like. These life forms apparently died out suddenly and simultaneously, and their extinction accords best with the asteroid theory. The fossil evidence of land dwellers, however, suggests a gradual decline in dinosaurian diversity, and possibly abundance, rather than a sudden change at the K-T boundary. Alterations in terrestrial life seem to be best accounted for by environmental factors such as the consequences of sea floor spreading and continental drift. With the rearrangement of the continental masses, disrupting and deflecting oceanic current patterns and causing repeated changes in sea level, there undoubtedly occurred many climatic changes, which in turn would have affected terrestrial organisms and their distribution.

Finally, in the controversy between the gradualist and catastrophist explanations of the dinosaurs' extinction, it should be noted that one phenomenon does not preclude the other. It is entirely possible that a culmination of ordinary biological changes and some catastrophic event both took place around the end of Cretaceous time.
 

About 50,000 earthquakes large enough to be felt or noticed without the aid of instruments occur annually over the entire Earth. Of these, approximately 100 are of sufficient size to produce substantial damage if their centers are near areas of habitation. Very great earthquakes occur at an average rate of about one per year. Among the great earthquakes of the past are those of Lisbon in 1755; New Madrid, Mo., U.S., in December 1811 and January and February 1812; San Francisco in 1906; Tokyo Yokohama in 1923; the coast of Chile in 1960; south central Alaska in 1964; T'ang-shan, China, in 1976; and Mexico in 1985. Their devastating effects are briefly described below.

Geographic concentrations of earthquakes.
The Earth's major earthquakes occur mainly in belts coinciding with the margins of tectonic plates (see below). This has long been apparent from early catalogs of felt earthquakes and is even more readily discernible in modern seismicity maps, which show instrumentally determined epicentres.One major earthquake belt passes around the Pacific Ocean and affects coastlines bordering on it, as, for example, those of New Zealand, New Guinea, Japan, the Aleutian Islands, Alaska, and the western regions of North and South America. It is estimated that 80 percent of the energy presently released in earthquakes comes from those whose epicenters are in this belt. The seismic activity is by no means uniform throughout the belt, and there are a number of branches at various points.

A second belt passes through the Mediterranean region eastward through Asia and joins the first belt in the East Indies. The energy released in earthquakes from this belt is about 15 percent of the world total. There also are striking connected belts of seismic activity, mainly along mid oceanic ridges including those in the Arctic Ocean, the Atlantic Ocean, and the western Indian Ocean--and along the rift valleys of East Africa.

Most other parts of the world experience at least occasional shallow earthquakes--those that originate within 60 kilometers of the Earth's outer surface. The great majority of earthquakes are shallow. It should be noted that the geographic distribution of smaller earthquakes is less precisely determined, partly because the availability of relevant data is dependent on the geographical distribution of observatories.

A distinction is made between "intermediate" focal depths ranging from about 60 to 300 kilometers and greater focal depths. Of the total energy released in earthquakes, 12 percent comes from intermediate earthquakes and 3 percent from deeper ones. The frequency of occurrence falls off rapidly with increasing focal depth in the intermediate range, while below this the distribution in depth is fairly uniform until the greatest focal depths are approached.

Deep focus earthquakes commonly occur in patterns called Benioff zones that dip into the Earth. Dip angles average about 45, with some shallower and others nearly vertical. Benioff zones are found under tectonically active island arcs, such as Japan, Vanuatu (formerly the New Hebrides), the Kingdom of Tonga (islands), and Alaska, and they are normally but not always (e.g., Romania and the Hindu Kush mountain system) associated with deep ocean trenches, such as those along the South American Andes. In most Benioff zones intermediate- and deep earthquake foci lie in a narrow layer, although recent precise hypo central locations in Japan and elsewhere show two distinct parallel bands of foci 20 kilometers apart. Careful estimation gives about 680 kilometers for the deepest depths globally.
 

T'ang-shan.
The coal mining and industrial city of T'ang-shan, located about 110 kilometers east of Peking, was almost razed in the tragic earthquake of July 28, 1976. The death toll exceeded 240,000 persons, and probably another 500,000 were injured. Most persons were killed from the collapse of unreinforced masonry homes, where they were asleep.
 

Energy and frequency of occurrence.
Energy in an earthquake passing a particular surface site can be calculated directly from the recordings of strong ground motion, which is given as ground velocity. Such recordings indicate an energy rate of 105 watts per square meter near a moderate sized earthquake source. The total power output of a rupturing fault in a shallow earthquake is on the order of 1014 watts compared with the 105 watts generated in rocket motors.The magnitude Ms has also been connected with the energy Es of an earthquake by empirical formulas. These give Es = 6.3  1011 and 1.4 1025 ergs for earthquakes of Ms = 0 and 8.9, respectively. A unit increase in Ms thus corresponds to a 32-fold increase in energy. Negative magnitudes correspond to the smallest instrumentally recorded earthquakes, a magnitude of 1.5 to the smallest felt earthquakes and one of 3 to any shock felt at a distance of up to 20 kilometers. Earthquakes of magnitude 5.0 cause light damage near the epicenter; those of 6 are destructive over a restricted area; and those of 7.5 are at the lower limit of major earthquakes.

The total annual energy released in all earthquakes is about 1025 ergs, corresponding to a rate of work between 10,000,000 and 100,000,000 kilowatts. This is on the order of 0.001 of the annual amount of heat escaping from the Earth's interior. Ninety percent of the total seismic energy comes from earthquakes of magnitude 7.0 and higher--i.e., those whose energy is on the order of 1023 ergs or more.

There also are empirical relations for the frequencies of earthquakes of various magnitudes. Suppose N to be the average number of shocks per year for which the magnitude lies in the range Ms +/- Ms. Then log10 N = a - bMs fits the data well both globally and for particular regions; e.g., for shallow earthquakes worldwide: a = 6.7, b = 0.9 when Ms > 6.0. The frequency for larger earthquakes therefore increases by a factor of about 10 when the magnitude is diminished by one unit. The increase in frequency with reduction in Ms falls short, however, of matching the decrease in the energy E. Thus larger earthquakes are overwhelmingly responsible for most of the total seismic energy release. The number of earthquakes per year with mb > 4.0 may reach 20,000.

 Some Great Earthquakes

Indonesia 2004
On Sunday, December 26, 2004 a massive 9.0 earthquake, centered in the Indian Ocean about 100 miles off the coast of Aceh, Indonesia, formed a tsunami that pummeled 11 countries causing thousands of deaths. The Tsunami toll could approach 150,000 to 200,000 after the earthquake which hit the region  5 million people ultimately will be affected by the disaster, including 1 million homeless.

Tokyo Yokohama 1923
A great earthquake struck the Tokyo- Yokohama metropolitan area near noon on Sept. 1, 1923. The death toll from this shock was estimated at more than 140,000. Fifty four percent of the brick buildings and 10 percent of the reinforced concrete structures collapsed. Many hundreds of thousands of houses were either shaken down or burned. The shock started a tsunami that reached a height of 12 meters at Atami on Sagami-nada (Sagami Gulf), where it destroyed 155 houses and killed 60 persons.

Mexico 1985
The main shock occurred at 7:18 AM on Sept. 19, 1985. The cause was a fault slip along the Benioff zone (a band of intermediate- and deep earthquake foci along a planar dipping zone) under the Pacific coast of Mexico. Although 400 kilometers from the epicenter, Mexico City suffered major building damage and more than 10,000 of its inhabitants were reported killed. The highest intensity was in the central city, which is founded on a former lake bed. The ground motion there measured five times that in the outlying districts, which have different soil foundations.

Alaska 1964
On March 27, 1964, a great earthquake with a Richter magnitude 8.3-8.5 (see below) occurred in south central Alaska. It released at least twice as much energy as the 1906 San Francisco earthquake and was felt on land over an area of almost 1,300,000 square kilometers. The death toll was only 131 because of the low density of the state's population, but property damage was very high. The earthquake tilted an area of at least 120,000 square kilometers. Landmasses were thrust up locally as high as 25 meters to the east of a line extending northeastward from Kodiak Island through the western part of Prince William Sound. To the west, land sank as much as 2.5 meters. Extensive damage in coastal areas resulted from submarine landslides and tsunamis. Tsunami damage occurred as far away as Crescent City, Calif. The occurrence of tens of thousands of aftershocks indicates that the region of faulting extended about 1,000 kilometers.

New Madrid 1811
Three large earthquakes occurred near New Madrid in southern Missouri on Dec. 16, 1811, and Jan. 23 and Feb. 7, 1812. There were numerous aftershocks, of which 1,874 were large enough to be felt in Louisville, Ky., some 300 kilometers away. The principal shock produced waves of sufficient amplitude to shake down chimneys in Cincinnati, Ohio, about 600 kilometers away. The waves were felt as far as Canada in the north and the Gulf Coast in the south. The area of greatest shaking was about 100,000 square kilometers, considerably greater than the area involved in the San Francisco earthquake in 1906. It has been discovered that in continental earthquakes such as the Missouri shocks, the area of strong shaking can be abnormally large compared with that in shocks along the Pacific coast of the United States. In one region 240 kilometers long by 60 kilometers wide, the ground sank from one to three meters and was covered by inflowing river water. Sand liquefaction effects were widespread. In certain locations, forests were overthrown or ruined by the loss of soil shaken from the roots of the trees.

San Francisco 1906
On April 18, 1906, at about 5:12 AM, the San Andreas Fault slipped over a segment about 430 kilometers long, extending from San Juan Bautista in San Benito County to the upper Mattole River in Humboldt County and from there perhaps out under the sea to an unknown distance. The shaking was felt from Los Angeles in the south to Coos Bay, Ore., in the north. Damage was severe in San Francisco and in other towns situated near the fault--e.g., San Jose, Salinas, and Santa Rosa (30 kilometers from the fault). Approximately 700 people were killed. In San Francisco the earthquake started a fire, which destroyed the central business district.

Lisbon 1755
On Nov. 1, 1755, Lisbon was heavily damaged by a great earthquake that occurred at 9:40 AM. The source was situated some distance off the coast. The violent shaking demolished large public buildings and about 12,000 dwellings. As November 1 was All Saint's Day, a large part of the population was attending religious services; most of the churches were destroyed, resulting in many casualties. The total number of persons killed in Lisbon alone was estimated to be as high as 60,000, including those who perished by drowning and in the fire that burned for about six days following the shock. Damage was reported in Algiers, 1,100 kilometers to the east. The earthquake generated a tsunami that produced waves about six meters high at Lisbon and 20 meters high at Cádiz, Spain. The waves traveled on to Martinique, a distance of 6,100 kilometers in 10 hours, and there rose to a height of four meters.

Chile 1960
The source of this earthquake in 1960 extended over a distance of about 1,100 kilometers along the southern Chilean coast. Casualties included about 5,700 killed and 3,000 injured, and property damage amounted to many millions of dollars. Seismic sea waves excited by the earthquake caused death and destruction in Hawaii, Japan, and the Pacific coast of the United States.

Nature or Acts of God such as Earthquakes, floods, Hurricanes, Tornadoes, Volcanic Eruptions and so forth still remain
the most threat to the extinction of the human race. The biggest loss of life due to a natural disaster, a flood in this case, occurred in 1938 in China on the Huang He River where 3,900,000 people were killed.. China also holds the largest
death toll due to the 1931 earthquake in the area of  Shaanxl in which 800,000 people were killed. The so-called "BIG ONE"
which is set to happen on the American west coast may happen by the year 2007.

----------------Major Earth Quakes since 1923-2004 and their Death Tolls.

December 26, 2004 Aceh, Indonesia magnitude 9.0, 150,000 to 200,000 killed-Sept. 1, 1923; Tokyo-Yokohama, Japan; magnitude 8.3; at least 140,000 killed / May 31, 1935; Quetta, India; magnitude 7.5; 50,000 killed. / Dec. 26, 1939; Erzincan province, Turkey; magnitude 7.9; 33,000 killed. / Jan. 24, 1939; Chillan, Chile; magnitude 8.3; 28,000 killed. / July 28, 1976; Tangshan, China; magnitude 7.8 to 8.2; 240,000 killed. / Feb. 4, 1976; Guatemala; magnitude 7.5; 22,778 killed. / Sept. 16, 1978; Northeast Iran; magnitude 7.7; 25,000 killed. / Sept. 19, 1985; Central Mexico; magnitude 8.1; more than 9,500 killed. /  Dec. 7, 1988; Northwest Armenia; magnitude 6.9; 25,000 killed. /June 21, 1990; Northwest Iran; magnitude 7.3 to 7.7; 50,000 killed. /  Dec 12, 1992  Indonesia A quake measuring 6.8 on the Richter scale killed at least 2,200 people on a string of islands in the province of East Nusa Tenggara. / Sept 30, 1993  India  A series of quakes killed almost 10,000 people in western and southern India. The first tremor measured 6.4. / June 6, 1994  Colombia  A quake brought down buildings and triggered mudslides, killing about 1,000 people in the Paez River valley in southwestern Colombia./ Jan 17, 1995 Japan A quake measuring 7.2, the country's worst in half a century, rocked Kobe, killing 6,430 people. /  May 28, 1995  Russia  Russia's worst earthquake, measuring 7.5, killed 1,989 people in the oil-producing Far East. / Feb 28, 1997  Iran A quake measuring 5.5 killed about 1,000 people in northwestern Iran. /  May 10, 1997  Iran A quake measuring 7.1 killed 1,560 people in rural areas of eastern Iran near the Afghan border. /  Feb 4, 1998  Afghanistan  At least 4,500 people were killed in Takhar province in a quake measuring 6.1. / July 17, 1998  Papula  New Guinea An undersea quake measuring 7.1 created three tidal waves that killed at least 2,100 people. /  Jan 25, 1999  Colombia. A quake measuring 6.3 killed at least 1,170 people in the central coffee-growing region. /  Aug 17, 1999  Turkey  More than 17,800 people were killed by a quake measuring 7.4. /  Sept 21, 1999  Taiwan At least 2,000 people were killed and hundreds of thousands made homeless by a quake measuring 7.6 in central Taiwan. /  Jan 26, 2001  India  An earthquake measuring 7.7 struck the western state of Gujarat killing at least 19,700 people and causing damage in neighbouring Pakistan. The quake affected 15.9 million people in 7,904 villages. / March 26, 2002  Afghanistan At least 1,500 people were killed when a series of earthquakes, measuring between five and six on the Richter scale, struck northern Afghanistan, destroying the district capital of Nahrin in the Hindu Kush mountains. /  June 22, 2002; Northwestern Iran, magnitude 6; at least 500 killed./
May 21, 2003  Algeria  An earthquake measuring 6.7 on the Richter scale strikes Algiers and nearby towns to the east, killing 2,251 and injuring 10,243. /  Feb 24, 2003; Western China, magnitude 6.3 or 6.8, at least 266 killed. / May 30, 1998 Afghanistan  A quake measuring 6.9 killed up to 4,000 people in northern Takhar province. /  Dec 26, 2003  Iran  An earthquake measuring 6.3 on the Richter scale strikes the historic city of Bam, 600 miles southeast of Tehran. Initial estimates suggested 30,000-35,000 people were killed.
---------------------
Most seismic activity occurs at the areas between tectonic plates. The dots above display earthquakes with a
minimum 5.5 of movement measured by the Richter scale. All the above earthquakes above have taken place since 1973 TO 2004.. Earthquakes of 6.5 to 7.5 on the Richter scale are considered the most powerful and dangerous depending on the area
in which they occur.

Tsunamis

Organizations, notably in Japan, Siberia, Alaska, and Hawaii, have been set up to provide tsunami warnings. A key development is the Seismic Sea Wave Warning System (SSWWS), an internationally supported system designed to reduce loss of life in the Pacific Ocean. Centered in Honolulu, it issues alerts based on reports of earthquakes from circum-Pacific seismographic stations.

HAZARDS FROM VARIOUS TYPES OF VOLCANIC ERUPTIONS

Gas clouds from a sudden increase in fumarole emissions may also contain poisonous or suffocating gases such as hydrogen sulfide, carbon monoxide, carbon dioxide, and sulfur dioxide. At a crater lake in Cameroon, West Africa, more than 1,700 people were killed by a sudden release of carbon dioxide in August 1986.

Ash falls from continued explosive jetting of fine volcanic particles into high ash clouds generally do not cause any direct fatalities. Yet, where the ash accumulates more than a few centimeters, collapsing roofs from ash loads and failure of crops are major secondary hazards. Crop failure can occur over large areas downwind from major Plinian eruptions, and widespread famine and disease may result, especially in poorly developed countries. Lightning strikes are common close to Plinian ash clouds, adding one more element of terror to an explosive eruption. (see also Index: volcanic ash)

Pyroclastic flows are the most dangerous and destructive aspect of explosive volcanism. They occur in many sizes and types, but their common characteristic is that they form a fluidized emulsion of volcanic particles, eruption gases, and entrapped air, resulting in a flow of low enough viscosity to be very mobile and of high enough density to hug the ground surface. A pyroclastic flow can pour over the lip of an erupting vent, or it may form when an ash cloud becomes too dense to continue rising and falls back to the ground. In major caldera collapses associated with explosive volcanoes, huge pyroclastic flows may issue from the ring fractures as the caldera block subsides.

Pyroclastic flows can move at speeds up to a few kilometers per minute and have temperatures ranging from 100 to 700 C. They sweep away and incinerate nearly everything in their path. Smaller pyroclastic flows are confined to valleys and are called nuées ardentes. Large pyroclastic flows may spread out as a blanket deposit across many hundreds or even thousands of square kilometers around a major caldera collapse. During the past 2,000,000 years, the Yellowstone National Park area has undergone three major caldera collapses involving pyroclastic eruptions of 300 to 3,000 cubic kilometers of rhyolitic magma.

Avalanches of rock and ice also are common on active volcanoes. They may occur with or without an eruption. Those without an eruption are often triggered by earthquakes, weakening of rock into clay by hydrothermal activity, or by heavy rainfall or snowfall. Those associated with eruptions are sometimes caused by oversteepening of a volcano's flank by intrusion of a shallow body of magma within or just beneath the volcanic cone, as happened at Mt. St. Helens.

A caldera collapse that is in part or entirely submarine usually generates a tsunami; the larger and more rapid the collapse, the larger the tsunami. Tsunamis also can be caused by avalanches or large pyroclastic flows rapidly entering the sea on the flank of a volcano.

Mud flows are common hazards associated with stratovolcanoes and can happen even without an eruption. They occur whenever floods of water mixed with ash, loose soil, or rocks that have been altered to clay by hydrothermal activity sweep down the valleys draining the sides of large stratovolcanoes. The huge mud flows generated by melt water from the ice cap of Nevado del Ruiz Volcano in 1985 are classic examples of mud flows associated with eruptions. Heavy rainfall or earthquake induced avalanches of ice or hydrothermal clay also can cause mud flows on steep volcanoes during periods of repose.

A lava flow engulfs and buries the land it covers, but new soil and vegetation eventually develop again. In warm humid climates the recovery is rapid; a few decades will hide the rocky surface of flows. In desert or arctic climates recovery is slower; flows more than 1,000 years old may still retain their barren appearance.

The greatest hazard at potentially active volcanoes is human complacency. The physical hazards can be reliably estimated by studying the past eruptive activity as recorded in history or in the prehistoric deposits around a volcano. Volcano observatories can monitor the local earthquake activity and the surface deformation of a potentially active volcano and make useful, if not yet precise, forecasts of eruptions. Increased earthquake activity beneath Mauna Loa in 1983 led to a forecast of an increase in probability of an eruption for 1984 or 1985; an eruption occurred in March 1984. The major eruption of Mt. St. Helens on May 18, 1980, was much larger than anticipated, but the high level of local earthquakes and the bulge forming on the north flank of the mountain provided enough warning to encourage a partial evacuation of the surrounding area. Some lives were lost, but the toll would have been much higher if access to the area had not been restricted by the local authorities. A major problem in reducing volcanic risk is that most explosive volcanoes have such long repose periods that people living nearby consider them extinct rather than dormant.

Bahasa Indonesia KRAKATAU, volcano on Pulau (island) Rakata in the Sunda Strait between Java and Sumatra, Indonesia. Its eruption in 1883 was one of the most catastrophic in history. Sometime within the past 1,000,000 years, the volcano built a cone shaped mountain composed of flows of volcanic rock alternating with layers of cinder and ash. From its base, 1,000 ft (300 m) below sea level, the cone projected about 6,000 ft above sea level. Later, the mountain's top was destroyed, forming a caldera, or bowl shaped depression, 4 mi (6 km) across. Portions of the caldera projected above the water as four small islands: Pulau Sertung (Verlaten) on the northwest, Lang and Polish Hat on the northeast, and Rakata on the south-southwest. Over the years, three new cones were formed, merging into a single island. The highest of the three cones rose to 2,667 ft above sea level.
The only known eruption prior to 1883 occurred in 1680; it was only moderate. On May 20, 1883, one of the cones again became active; ash laden clouds reached a height of 6 mi, and explosions were heard in Batavia, (Jakarta), 100 mi away, but by the end of May the activity had died down. It resumed on June 19 and became paroxysmal by August 26. At 1:00 PM of that day the first of a series of increasingly violent explosions occurred, and at 2:00 PM a black cloud of ash rose 17 mi above Krakatoa. The climax was reached at 10:00 AM on August 27, with tremendous explosions that were heard 2,200 mi away in Australia and propelled ash to a height of 50 mi. Pressure waves in the atmosphere were recorded around the Earth. Explosions diminished throughout the day, and by the morning of August 28, the volcano was quiet. Small eruptions continued in the following months and in February 1884.

The discharge of Krakatoa threw into the air nearly 5 cu mi (21 cu km) of rock fragments, and large quantities of ash fell over 300,000 sq mi (800,000 sq km). Near the volcano, masses of floating pumice were so thick as to halt ships. The surrounding region was plunged into darkness for two and a half days because of ash in the air. The fine dust drifted several times around the Earth, causing spectacular red sunsets throughout the following year.

After the explosion, only a 2,667-ft-high islet remained in a basin covered by 900 ft of ocean water. As much as 200 ft of ash and pumice fragments had accumulated on Verlaten and Lang islands and on the remaining southern part of Rakata. Analysis of this material revealed that very little of it consisted of debris from the former central cones: the fragments of old rock in it represented less than 10 percent of the volume of the missing part of the island. Most of the material was new magma brought up from the depths of the Earth, most of it distended into pumice by expansion of the gas it contained or completely blown apart to form ash. Thus, the former volcanic cones were not blown into the air, as was first believed, but instead, sank out of sight as the top of the volcano collapsed because of the removal of a large volume of magma from the underlying reservoir.

The volcano's collapse triggered a series of tsunamis, or tidal waves, recorded as far away as South America and Hawaii. The greatest wave, which reached a height of 120 ft and took 36,000 lives in nearby coastal towns of Java and Sumatra, occurred just after the climactic explosion. All life on the Krakatoa island group was buried under a thick layer of sterile ash, and reestablishment of plant and animal life did not begin for five years.

Krakatoa was quiet until Dec. 29, 1927, when a new eruption began on the sea floor along the same line as the previous cones. By Jan. 26, 1928, a growing cone had reached sea level and formed a small island called Anak Krakatoa (Child of Krakatoa). Sporadic activity continued until, by 1973, the island had reached a height of 622 ft above sea level. It was still in eruption in the early 1980s.

-EL NINO & GLOBAL WARMING-

1999 Winter Sets U.S. Record For Warmth

Sir John Houghton,of the Intergovernmental Panel predicts the sea level is likely to rise by about half a meter by
the year 2100 and that will lead to a more intense hydrological cycle.In laymen terms this means areas with
heavy rain fall will intensify while global areas with little rain fall will receive even less.The ecology summit held
in 1997 at Kyoto,Japan where the world's industrial nations agreed to try and lessen the green house effect will
need to step up their plans on the lessening of global emissions. The amount of carbon dioxide has already
increased by 30% since 1750 and if no action is taken soon,it will increase 60% by the middle of this century
making ecology one of the world's top priority concerns of the next century. Many scientists have already
stated that the world's fresh water supply will be in serious shortage by the year 2025 and will not be able to
supply the basic needs of 18 nations in the MidEast. This surely will cause conflict between nations including
Iran, Iraq, Israel and the Palestine area (as if they needed more issues to deal with as it is.) and cause tension
world wide if drastic measures are not taken immediately by everyone.If anything would cause a world panic
it would be the shortage of water.Look what happened when oil was in short supply.

The invasion of Kuwait in 1990 by Iraq leader Suddam Hussein which brought the armies of the world to drive him out
had little to do with the liberation of Kuwait- but more like the stopping of a ruthless leader controlling the Persian Gulf
in which most of the world's oil supply comes from. Oil is the second largest financial business in the world and to let a
dictator try and control it would be disastrous. With Military weaponry as the world's largest economic business and
drugs follow up in third  I foresee global water shortages as a possibility to future global conflict within the next 20 years
at which time a estimated 8 to 12 more nations in the world will have nuclear war head capabilities.
 

Warmer Oceans Killing Marine Life
     June 9, 1999
                         Ocean 3 degrees warmer

 "These disturbing results demonstrate that global warming is coming home to roost," said Adam Markham,
director of the wildlife fund's climate program. "The story will only get worse unlessgovernments and
business take the steps to stop it."Ocean temperatures have risen three degrees Fahrenheit in some places
over the past 60 years and will rise another 5.5 degrees over the next century if greenhouse gas emissions
continue to grow at current rates, the  report said.

Global warming has coincided with an increased incidence of the El Niño phenomenon, in which warm
water concentrated in the eastern Pacific creates volatile weather patterns, it said. Centuries ago El Niño
occurred every two to 15 years,but the pattern was repeated five times between 1990 and 1997 and record
high global average temperatures were recorded in 1997 and 1998,the report said.The oceanic heat has
devastated coral reefs and ice shelves that house species including algae, plankton and crustaceans,
cutting the food supply to larger animals including whales, penguins and sea lions, it said. Rising sea levels
also threaten to ruin coastal wetlands and other habitats that support marine animals and commercial fisheries,
the report concluded.

  1999 Acid Rain Report Exposes Serious Health Hazards

1998 Atlantic Hurricane Season Death Toll Highest In 200 Years

         The El Niño Phenomenon

The shortest, or interannual, time scale relates to natural variations that are perceived as years of unusual weather--e.g., excessive heat, drought, or storminess. Such changes are so common in many regions that any given year is about as likely to be considered as exceptional as typical. The best example of the influence of the oceans on interannual climate anomalies is the occurrence of El Niño conditions in the eastern Pacific Ocean at irregular intervals of about 3-10 years. The stronger El Niño episodes of enhanced ocean temperatures (2-8 C above normal) are typically accompanied by altered weather patterns around the globe, such as droughts in Australia, northeastern Brazil, and the highlands of southern Peru, excessive summer rainfall along the coast of Ecuador and northern Peru, severe winter storminess along the coast of central Chile, and unusual winter weather along the west coast of North America.The effects of El Niño have been documented in Peru since the Spanish conquest in 1525. The Spanish term "la corriente de El Niño" was introduced by fishermen of the Peruvian port of Paita in the 19th century; it refers to a warm, southward ocean current that temporarily displaces the normally cool, northward-flowing Humboldt, or Peru, Current. (The name is a pious reference to the Christ child, chosen because of the typical appearance of the countercurrent during the Christmas season.) By the end of the 19th century Peruvian geographers recognized that every few years this countercurrent is more intense than normal, extends farther south, and is associated with torrential rainfall over the otherwise dry northern desert. The abnormal countercurrent also was observed to bring tropical debris, as well as such flora and fauna as bananas and aquatic reptiles, from the coastal region of Ecuador farther north. Increasingly during the 20th century, El Niño has come to connote an exceptional year rather than the original annual event.

As Peruvians began to exploit the guano of marine birds for fertilizer in the early 20th century, they noticed El Niño-related deteriorations in the normally high marine productivity of the coast of Peru as manifested by large reductions in the bird populations that depend on anchovies and sardines for sustenance. The preoccupation with El Niño increased after mid-century, as the Peruvian fishing industry rapidly expanded to exploit the anchovies directly. (Fish meal produced from the anchovies was exported to industrialized nations as a feed supplement for livestock.) By 1971 the Peruvian fishing fleet had become the largest in its history; it had extracted very nearly 13 million metric tons of anchovies in that year alone. Peru was catapulted into first place among fishing nations, and scientists expressed serious concern that fish stocks were being depleted beyond self-sustaining levels, even for the extremely productive marine ecosystem of Peru. The strong El Niño of 1972-73 captured world attention because of the drastic reduction in anchovy catches to a small fraction of prior levels. The anchovy catch did not return to previous levels, and the effects of plummeting fish meal exports reverberated throughout the world commodity markets.

El Niño was only a curiosity to the scientific community in the first half of the 20th century, thought to be geographically limited to the west coast of South America. There was little data, mainly gathered coincidentally from foreign oceanographic cruises, and it was generally believed that El Niño occurred when the normally northward coastal winds off Peru, which cause the upwelling of cool, nutrient-rich water along the coast, decreased, ceased, or reversed in direction. When systematic and extensive oceanographic measurements were made in the Pacific in 1957-58 as part of the International Geophysical Year, it was found that El Niño had occurred during the same period and was also associated with extensive warming over most of the Pacific equatorial zone. Eventually tide-gauge and other measurements made throughout the tropical Pacific showed that the coastal El Niño was but one manifestation of basinwide ocean circulation changes that occur in response to a massive weakening of the westward-blowing trade winds in the western and central equatorial Pacific and not to localized wind anomalies along the Peru coast.

EL NIÑO/SOUTHERN OSCILLATION AND CLIMATIC CHANGE

Studies suggest that the ENSO can affect mid-latitude climates, modulating the position and intensity of the polar-front jet stream (see above). An El Niño event that began in early 1982 lasted well into 1983. It was accompanied by unusual weather events outside of the equatorial Pacific region. Western Europe suffered from record summer heat. Late-fall temperatures in the United States were very cold; winter was mild; spring rains were far above normal and spring temperatures in the central part of the country were extremely cold; and summer conditions in the Midwest and Southeast were extremely hot and dry. These abnormal weather conditions were consistent with a shift in the jet-stream pattern away from its normal one and were with little doubt caused in part by the intense El Niño.

The ENSO appears to be a truly disruptive force that wreaks havoc on life. In 1982-83 it not only caused the drought in Australia and the flooding along the western coast of South America and the loss of the anchovy catch there, but it also damaged corn, soybean, and other summer crops in the United States, which resulted in losses amounting to billions of dollars. Clearly a better understanding of the El Niño and its associated atmospheric effects is needed, leading perhaps to predictive skill.

As was explained earlier, the oceans can moderate the climate of certain regions. Not only do they affect such geographic variations, but they also influence temporal changes in climate. The time scales of climate variability range from a few years to millions of years and include the so-called ice age cycles that repeat every 20,000 to 40,000 years, interrupted by interglacial periods of "optimum" climate, such as the present. The climatic modulations that occur at shorter scales include such periods as the Little Ice Age from the early 16th to the mid-19th centuries, when the global average temperature was approximately 1 C lower than it is today. Several climate fluctuations on the scale of decades have occurred in the 20th century, such as warming from 1910 to 1940, cooling from 1940 to 1970, and the warming trend since 1970.
Although many of the mechanisms of climate change are understood, it is usually difficult to pinpoint the specific causes. Scientists acknowledge that climate can be affected by factors external to the land-ocean-atmosphere climate system, such as variations in solar brightness, the shading effect of aerosols injected into the atmosphere by volcanic activity, or the increased atmospheric concentration of "greenhouse" gases (e.g., carbon dioxide, nitrous oxide, methane, and chlorofluorocarbons) produced by human activities. However, none of these factors explain the periodic variations observed during the 20th century, which may simply be manifestations of the natural variability of climate. The existence of natural variability at many time scales makes the identification of causative factors such as human-induced warming more difficult. Whether change is natural or caused, the oceans play a key role and have a moderating effect on influencing factors.
 

        Studying the Causes of Droughts and other Climatic Patterns

Upwelling

CIRCULATION, CURRENTS, AND OCEAN-ATMOSPHERE INTERACTION

The ocean, particularly in areas where the surface is warm, also supplies moisture to the atmosphere. This in turn contributes to the heat budget of those areas in which the water vapour is condensed into clouds, liberating latent heat in the process, frequently in high latitudes and in locations remote from the ocean where the moisture was taken up.

The great ocean currents are themselves wind-driven--set in motion by the drag of the winds over vast areas of the sea surface, especially where waves increase the friction. At the limits of the warm currents, particularly where they abut directly upon a cold current, as at the left flank of the Gulf Stream in the neighbourhood of the Grand Banks off Newfoundland and at the subtropical and Antarctic convergences in the oceans of the Southern Hemisphere, the strong thermal gradients in the sea surface result in marked differences in the heating of the atmosphere on either side of the boundary. These temperature gradients tend to position and guide the strongest flow of the jet stream (see below Jet streams) in the atmosphere above and thereby influence the development and steering of weather systems.

Interactions between the ocean and the atmosphere proceed in both directions. They also operate at different rates. Some interesting lag effects, which are of value in long-range weather forecasting, arise through the considerably slower circulation of the ocean. Thus, enhanced strength of the easterly trade winds over low latitudes of the Atlantic, north and south of the Equator, impels more water toward the Caribbean and Gulf of Mexico, producing a stronger flow and greater warmth in the Gulf Stream approximately six months later. Anomalies in the position of the Gulf Stream-Labrador Current boundary, which produce a greater or lesser extent of warm water near the Grand Banks, so affect the energy supply to the atmosphere and the development and steering of weather systems from that region that they are associated with rather persistent anomalies of weather pattern over the British Isles and northern Europe. Anomalies in the equatorial Pacific and in the northern limit of the Kuroshio (also called the Japan Current) seem to have effects on a similar scale. Indeed, through their influence on the latitude of the jet stream and the wavelength (that is, the spacing of cold trough and warm ridge regions) in the upper westerlies, these ocean anomalies exercise an influence over the atmospheric circulation that spreads to all parts of the hemisphere.

Sea-surface temperature anomalies that recur in the equatorial Pacific at variable intervals of two to seven years can sometimes produce major climatic perturbations. Such an anomaly is known as El Niño (Spanish for "The Child"; it was so named by Peruvian fishermen who noticed its onset during the Christmas season).

During an El Niño event, warm surface water flows eastward from the equatorial Pacific, in at least partial response to weakening of the equatorial easterly winds, and replaces the normally cold upwelling surface water off the coast of Peru and Ecuador that is associated with the northward propagation of the cold Peru (or Humboldt) Current. The change in sea-surface temperature transforms the coastal climate from arid to wet. The event also affects atmospheric circulation in both hemispheres and is associated with changes in precipitation in regions of North America, Africa, and the western Pacific.
 

Adverse Effects of Global Weather Conditions

The Atmosphere

The atmosphere extends from the surface of the Earth to heights of thousands of kilometres, where it gradually merges with the solar wind--a stream of charged atomic particles that flows outward from the outermost regions of the Sun. The composition of the atmosphere is more or less constant with height to an altitude of about 100 kilometres.

The atmosphere is commonly described in terms of distinct layers, or regions. Most of the atmosphere is concentrated in the troposphere, which extends from the surface to an altitude of about 15 kilometres. The behaviour of the gases in this layer is controlled by convection. This process involves the turbulent, overturning motions resulting from buoyancy of near-surface air that is warmed by the Sun. Convection maintains a vertical temperature gradient (i.e., temperatures decline with altitude) of roughly 6 C per kilometre (10.8 F per kilometre) through the troposphere. At the top of the troposphere, which is called the tropopause, temperatures fall to about -60 C (-76 F). The troposphere is the region where virtually all water vapour exists and where all weather occurs.

The dry, tenuous stratosphere lies above the troposphere and extends to an altitude of about 50 kilometres. Convective motions are weak or absent in the stratosphere; motions instead tend to be horizontally oriented. The temperature in this layer increases with altitude.

In the upper stratospheric regions, absorption of ultraviolet light from the Sun breaks down oxygen molecules; recombination of oxygen atoms with O2 molecules into ozone (O3) creates the ozone layer, which shields the lower ecosphere from harmful short-wavelength radiation.

Above the relatively warm stratopause is the even more tenuous mesosphere, in which temperatures again decline with altitude, reaching roughly -85 C at the mesopause. Temperatures then rise with increasing height through the overlying layer known as the thermosphere. Above about 100 kilometres, in the ionosphere, there is an increasing fraction of charged, or ionized, particles. Spectacular visible auroras are generated in this region, particularly along circular zones around the poles, by episodic precipitation of energetic particles.

The general circulation of the Earth's atmosphere is driven by solar energy, which falls preferentially in equatorial latitudes. Atmospheric redistribution of heat poleward is strongly affected by the Earth's rapid rotation and the associated Coriolis force at nonequatorial latitudes (which adds an east-west component to the direction of the winds), resulting in about three latitudinal cells of circulation in each hemisphere. Instabilities produce the characteristic high-pressure areas and low-pressure storms of the mid-latitudes as well as the fast, eastward-moving jet streams of the upper troposphere that guide the paths of storms. The oceans are massive reservoirs of heat, and their slowly changing currents and temperatures also influence weather and climate, as in the so-called El Niño episodes (see OCEANS: Impact of ocean-atmosphere interactions on weather and climate: The El Niño phenomenon). (see also Index: atmospheric circulation, ocean-atmosphere interaction)

The Earth's atmosphere is not a static feature of the environment. Rather its composition has evolved over time in concert with life and continues to change as human activities alter the ecosphere. Roughly halfway through the history of the Earth, the atmosphere's unusual complement of free oxygen began to develop owing to photosynthesis by blue-green algae and subsequently evolving plant life. Accumulation of oxygen eventually made it possible for respirating animals to move out onto the land.

The Earth's climate at any location varies with the seasons, but there are also longer-term variations in global climate. Volcanic explosions, such as the 1991 eruption of Mount Pinatubo in the Philippines, can inject great quantities of particulates into the stratosphere, which remain suspended for years, decreasing atmospheric transparency and resulting in measurable cooling worldwide. Rare, giant impacts of asteroids and comets can have even more profound effects. The dominant climate variations observed in the recent geologic record are the ice ages, which are linked to small variations in the Earth's geometry with respect to the Sun. (see also Index: volcanic eruption)

The Sun is believed to have been less luminous during the early history of the Earth, so if other planetary conditions were identical with those of today, the oceans would have been frozen. But it is expected that there was much more carbon dioxide in the Earth's atmosphere during earlier periods, which would have enhanced greenhouse warming. In this phenomenon, heat radiated by the surface is trapped by gases such as carbon dioxide in the atmosphere and reradiated back to the surface, thereby warming it. There is presently 105 times more carbon dioxide buried in carbonate rocks in the Earth's crust than in the atmosphere, in sharp contrast with Venus, whose atmospheric evolution followed a different course. (see also Index: greenhouse effect)

The amount of carbon dioxide in the atmosphere is rising steadily, however, and has increased by more than 10 percent in the last 30 years owing to the burning of fossil fuels (e.g., coal, oil, and natural gas) and the destruction of tropical rain forests, such as that of the Amazon River basin. A further doubling by the middle of the 21st century could lead to a global warming of a few degrees, which would have profound effects on the sea level and on agriculture.

Of more immediate concern is the impact of human activities on the stratospheric ozone layer. Complex chemical reactions involving traces of man-made chlorofluorocarbons have recently created temporary holes in the ozone layer, particularly over Antarctica, during polar spring. More disturbing, however, is the discovery of a growing depletion of ozone over temperate latitudes, where a large percentage of the world's population resides, since the ozone layer serves as a shield against ultraviolet radiation, which has been found to cause skin cancer.

GREENHOUSE EFFECT INDUCED BY CARBON DIOXIDE AND OTHER TRACE GASES

In spite of these long-term possibilities, the greenhouse problem has received the least policy-oriented attention of any of the three major issues at hand. There are various reasons for this: (1) The problem is fraught with technical uncertainties. (2) It has perceived "winners" and "losers"--economic and otherwise. (3) No one nation acting alone can do much to counteract the CO2 buildup in the atmosphere. (4) Dealing with the problem substantively could be expensive and even alter life-styles. (5) There is no way of proving the validity of the greenhouse theory to everyone's satisfaction except by "performing the experiment" on the real climatic system, which would necessarily involve all living things on Earth. (6) The principal greenhouse gas, CO2, is an inherent by-product of the utilization of a commodity that is most fundamental to the economic viability of the world--fossil-fuel energy. (This fact more than any other explains why the greenhouse problem is so difficult to solve.)

It seems appropriate to break down the issue of greenhouse warming into a series of stages and then consider how policy questions might be addressed against the background of these more technical stages. The present discussion will deal with the problem specifically as it relates to increasing atmospheric CO2 for the sake of simplicity, though other related questions certainly can be dealt with in the same manner.

Glaciers and Sea Level

(UNCED), byname EARTH SUMMIT, conference held at Rio de Janeiro, Brazil (June 3-14, 1992), to reconcile worldwide economic development with protection of the environment. The Earth Summit was the largest gathering of world leaders in history, with 117 heads of state and representatives of 178 nations in all attending. By means of treaties and other documents signed at the conference, most of the world's nations nominally committed themselves to the pursuit of economic development in ways that would protect the Earth's environment and nonrenewable resources.The main documents agreed upon at the Earth Summit are as follows. The Convention on Biological Diversity is a binding treaty requiring nations to take inventories of their plants and wild animals and protect their endangered species. The Framework Convention on Climate Change, or Global Warming Convention, is a binding treaty that requires nations to reduce their emission of carbon dioxide, methane, and other "greenhouse" gases thought to be responsible for global warming; the treaty stopped short of setting binding targets for emission reductions, however. The Declaration on Environment and Development, or Rio Declaration, laid down 27 broad, nonbinding principles for environmentally sound development. Agenda 21 outlined global strategies for cleaning up the environment and encouraging environmentally sound development. The Statement of Principles on Forests, aimed at preserving the world's rapidly vanishing tropical rainforests, is a nonbinding statement recommending that nations monitor and assess the impact of development on their forest resources and take steps to limit the damage done to them.

The Earth Summit was hampered by disputes between the wealthy industrialized nations of the North (i.e., western Europe and North America) and the poorer developing countries of the South (i.e., Africa, Latin America, the Middle East, and parts of Asia). In general, the countries of the South were reluctant to hamper their economic growth with the environmental restrictions urged upon them by the North unless they received increased Northern financial aid, which they claimed would help make environmentally sound growth possible.

Biological productivity.

The Ozone

Ozone is 1.5 times as dense as oxygen; at -112 C (-170 F) it condenses to a dark blue liquid, which freezes at -251.4 C (-420 F). The gas decomposes rapidly at temperatures above 100 C (212 F) or, in the presence of certain catalysts, at room temperatures. Although it resembles oxygen in many respects, ozone is much more reactive; hence, it is an extremely powerful oxidizing agent, particularly useful in converting olefins into aldehydes, ketones, or carboxylic acids. Because it can decolorize many substances, it is used commercially as a bleaching agent for organic compounds; as a strong germicide it is used to sterilize drinking water as well as to remove objectionable odours and flavours
 

Depletion of stratospheric ozone.

The debate concerning the environmental impact of the SST has had a lasting effect on the development of atmospheric science, spawning a new interdisciplinary program of research linking chemists, physicists, and biologists in a common effort to understand the stratosphere. The program, with international participation, has been remarkably successful and has led to a new view of the interdependence of the atmosphere, hydrosphere, and biosphere.

The concern over the effects of exhaust gases from supersonic aircraft was soon followed by a new issue: the possibility that chlorine atoms released by decomposition of chlorofluorocarbons could have a larger and more persistent effect on stratospheric ozone. CFC's were developed first in the 1930s but found widespread use only in the years following World War II. They were employed with great success by U.S. troops in the Pacific to dispense insecticides from aerosol spray cans. This led to many commercial uses, from propellants and refrigerants to foaming agents and degreasers and a host of other applications. Moreover, the use of CFC's rapidly spread from the United States to Europe and the Far East. All this changed in 1975, when it was recognized that the release of CFC's to the atmosphere could pose a serious problem for stratospheric ozone. Production of F-12 declined from a peak of about 4.5 105 metric tons in 1975 to about 3.4 105 metric tons in 1982. A similar drop was registered for F-11.

Much of the work undertaken since the mid-1970s has focused on the effects of CFC's on the assumption that the composition of the atmosphere was otherwise constant. It has become clear, however, that the response of ozone depends not simply on the abundance of CFC's but also on the abundances of methane, nitrous oxide, and carbon monoxide. These species, too, are changing. Current models suggest that a continuing release of CFC's at the rate registered in 1980, other gases remaining constant, would lead to a reduction in stratospheric ozone by about 5 percent. Maximum impact is predicted to occur at altitudes above 25 kilometres. An increase in nitrous oxide of 20 percent is expected to cause a reduction in ozone of about 2 percent. An increase in carbon dioxide should lead to a reduction in stratospheric temperatures with a consequent reduction in the anticipated impact of CFC's and nitrous oxide on ozone. The effect of an increasing burden of methane is more complex. Oxidation of methane provides a source of ozone at low altitude, while the reaction of chlorine with methane converts chlorine radicals to hydrogen chloride, resulting in a reduction in the impact of CFC's between 30 and 40 kilometres.

Models suggest that the change in the column density of stratospheric ozone to date should be relatively small. Reductions in ozone at high altitude, near 40 kilometres, ought to be balanced by excess production at low altitudes due in part to the higher level of methane and in part to NOx released by high-altitude aircraft. Observational evidence is consistent with this view. A statistical analysis concluded that the change in the ozone column from 1970 to 1983 averaged -0.003 percent per decade. It showed, however, that a small though statistically significant drop in ozone--a decline of about 2 percent--occurred at altitudes above 30 kilometres between 1970 and 1980.

There has been a new development since 1985. That year, Joseph C. Farman and his associates at the British Antarctic Survey reported that the level of ozone over Antarctica had dropped precipitously every October since 1982, with the first such change apparent as early as 1978. A number of theories, or more properly hypotheses, have been advanced to account for this phenomenon. Several implicate effects of anthropogenic chlorine, enhanced by small quantities of bromine. Others suggest that the reduction may be due to a diminished supply of ozone from low latitudes, reflective of a change in stratospheric dynamics. In any case, the phenomenon was quite unexpected and serves as a powerful warning that current scientific understanding of the stratosphere is still rudimentary.
 

OZONE DEPLETION

By the mid-1970s, various U.S. investigators had determined that chlorofluorocarbons (CFCs), widely employed as propellants in aerosol spray cans, could reduce the amount of stratospheric ozone significantly. A temporary ban was imposed on the use of certain CFCs in the United States, but only after much emotional debate among environmental and industrial scientists, reports by the National Academy of Sciences, and the development by industry of economically viable substitutes for spray-can propellants.
 

Toxic chemicals.

Sulfur dioxide results primarily from the burning of large amounts of soft coal and high-sulfur oil. It is toxic to a wide range of plants at concentrations as low as 0.25 part per million (ppm) of air (i.e., on a volume basis, one part per million represents one volume of pure gaseous toxic substance mixed in one million volumes of air) for 8 to 24 hours. Gaseous and particulate fluorides are more toxic to sensitive plants than is sulfur dioxide because they are accumulated by leaves. They are also toxic to animals that feed on such foliage. Fluorine injury is common near metal-ore smelters, refineries, and industries making fertilizers, ceramics, aluminum, glass, and bricks.

Ozone and peroxyacetyl nitrate injury (also called oxidant injury) are more prevalent in and near cities with heavy traffic problems. Exhaust gases from internal combustion engines contain large amounts of hydrocarbons (substances that principally contain carbon and hydrogen molecules--gasoline, for example). Smaller amounts of unconsumed hydrocarbons are formed by combustion of fossil fuels (e.g., coal, oil, natural gas) and refuse burning. Ozone, peroxyacetyl nitrate, and other oxidizing chemicals (smog) are formed when sunlight reacts with nitrogen oxides and hydrocarbons. This pollutant complex is damaging to susceptible plants many kilometres from its source. Ozone and peroxyacetyl nitrate are capable of causing injury if present at levels of 0.01 to 0.05 part per million for several hours.

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