Reptiles

Crocodiles, too, regulate their body temperature on land by varying their position relative to the Sun's rays. They also open their mouths to increase heat loss by evaporation. If the temperature becomes too high, they move into the water which is relatively cooler. At night they retreat to water in order to avoid the low temperatures which would be experienced on land. Regularization mechanisms have been studied most extensively in lizards. Many different species of lizard have been studied and show a variety of responses to different temperatures. Lizards are terrestrial reptiles and exhibit many behavioral activities, as is typical of other isotherms. Some species, however, use a number of physiological mechanisms to raise and maintain their body temperatures above that of the environment. Other species are able to keep their body temperature within confined limits by varying their activity and taking advantage of shade or exposure. In both these respects lizards foreshadow many of the mechanisms of thermometer shown by birds and mammals. 

Surface temperatures in desert regions can rise to 70-80 °C during the day and fall to 4 °C at dawn. During the periods of extreme temperatures, most lizards seek refuge by living in burrows or beneath stones. This response and certain physiological responses are shown by the horned lizard (Chromosomal) which inhabits the deserts of the south-west of the USA and Mexico. In addition to burrowing, the horned lizard is able to vary its orientation and color, and as the temperature becomes high it can also reduce its body surface area by pulling back its ribs. Other responses to high temperatures involve panting, which removes heat by the evaporation of water from the mouth.

THE SKELETAL SYSTEM

The 206 bones of the body make up a working whole called the skeleton, or skeletal system. Together, the bones of the skeleton perform many important functions, some of which have already been mentioned. To summarize:The skeletal system provides support for the body otherwise you would be a shapeless blob of skin covered tissues and organs. It also provides for movement, with individual bones serving as points of attachment for the skeletal muscles and acting as levers against which muscles can pull.Delicate internal structures are protected by the skeleton. The brain, for example, lies within a strong, bony casing called the skull; the rib cage surrounds and protects the heart and lungs.The bones of the skeleton are a storehouse for minerals such as calcium and phosphorus.

Amazingly, bone tissue is continually broken down and reformed, the mineral salts being transported to other parts of the body on demand. In fact, scientists have estimated that your body completely "replaces" your skeleton over a period of 7 years! Lastly, certain inner portions of bones contain red marrow and arc your internal factory of blood cells. Without this factory you would die, since red blood cells have a short life span of approximately 120 days. Without these cells your body would have no efficient means to transport life giving oxygen to your tissues. 'White blood cells are also produced in the red bone marrow. One of the main jobs of certain classes of these cells is to ingest bacteria and debris.

Archaeal Genomes Combine Features Of Bacteria and Eukaryotes

Like bacteria, Archean have polytechnic opens, and their reproduction is predominantly asexual. Archean are true protectorates in that their cells lack a nuclear membrane. On the other hand, in most species of Archean, the structures of the DNA packing proteins, RNA polymer, and chromosomal components more closely resemble those of Prokaryotic. Even the DNA polymer and the origin recognition sequence show greater similarity to those of Prokaryotic. Finally, it should be noted that charcoal genomes encode certain unique components such as the metabolic pathway of parthenogenesis. Carbon Trading news in freshsciencenews For more on Archean, What experimental data allow us to make such comparisons? Overwhelmingly, we rely on new data from the growing number of microbial genomes sequenced. Comparison of genomes has revolutionized our understanding of evolutionary relationships among microbes. We will now examine the tools of DNA sequence analysis that have made these studies possible. The most important of these tools restriction mapping, DNA sequencing, and amplification by the polymer chain reactionactually harness the molecular apparatus used by bacteria to replicate or protect their own chromosomes. 

DNA Sequence Analysis 

We have just described the core concepts of DNA structure, packaging, and replication. This knowledge is crucial to understanding genomics and the fundamentals of gnomic analysis. It is now appropriate to discuss the basic techniques used to manipulate DNA. These include isolating gnomic DNA from cells, snipping out DNA fragments with surgical precision, splicing them into plasma vehicles, and reading their polynucleotide sequences. These are the techniques that drove the gnomic revolution.

study of behaviour (ethology)

Behaviour may be defined as the outwardly expressed course of action produced in organisms in response to stimuli from a given situation. The action modifies, in some way, the relationship between the organism and its environment and its adaptive significance is the perpetuation of the species. All living organisms exhibit a variety of forms of behaviorism activity deter-mined by the extent to which they are able to respond to stimuli. This varies from the relatively simple action of the growth of a plant stem towards a light source, to the complex sexual behavior patterns of territory defense, courtship and mating seen in birds and mammals. Plant behavior is restricted to movements produced by growth or turgid changes and is stereotyped and predictable. The two main activities associated with plant behavior are tropisms and taxes and details of these are described in section. Animal behavior is far more complex and diverse than plant behavior and therefore it is extremely difficult to investigate and account for with any degree of scientific validity. The three main approaches to behavioral studies are the capitalistic, mechanistic and ethological approaches. 

Vitalistic approach

This seeks to account for behavioral activities in terms of what animals are seen to do, and attempts to relate this to changes in the environment. It involves the total rejection of any study of the animal outside its natural environment. The technique has its foundations in natural history and has provided a wealth of valuable data, but it is essentially non scientific since all the observations relate to past events which cannot be tested experimentally.

The meninges and cerebrospinal fluid....

The central nervous system is surrounded by three layers or 'membranes' called meninges  and is completely encased within the protective bones of the skull and vertebral column. The outer membrane forms the tough dun mater which is attached to the skull and vertebrae, and the inner membrane forms the thin Pia mater which lies next to the nervous tissues. Between the two is the arachnid 'membrane'. This includes a space, the arachnophobia space, strands of connective tissue, blood vessels and cerebrovascular fluid (CS). Most of this fluid is contained in the central canal of the spinal cord and continues forward to occupy four expanded cavities within the brain called the ventricles. The fluid therefore comes into contact with the outside and inside of the brain, and blood vessels lie within it for the supply of nutrients and oxygen to the nervous tissues and the removal of wastes. It also contains lymphocytes to protect against infection. Meningitis is caused by an infection of the meninges. About 100 cm3 of fluid is present in the CNS and, apart from its nutritive, excretory and defensive functions, it supports the nervous tissues and protects them against mechanical shock. A continual circulation of fluid is maintained by cilia ted cells lining the ventricles and central canal. 

The Spinal Cord

The spinal cord is a cylinder of nervous tissue running from the base of the brain down the back. It is protected by the vertebrae of the backbone (vertebral column) and the meninges. It has a shaped central area of grey matter, composed of nerve cell bodies, dendrites and synapses surrounding a central canal which contains cerebrovascular fluid. Around the grey matter is an outer layer of white matter, containing nerve fibers whose fatty myelitis sheaths give it its characteristic color. There are 31 pairs of spinal nerves and these divide dose to the spinal cord to form two branches called the dorsal root and ventral root. 

 

The hip and thigh

The lower limb, similar in structure to the upper, is modified by its functions of support and propulsion of the body. During its development there is rotation medially on its long axis, so that the flexion surface lies posterior and the sole of the foot faces backwards and then downwards. The pelvic girdle, unlike the pectoral girdle, is firmly attached to the vertebral column, which allows the transmission of the body's weight through it to the lower limb. In the standing position the center of gravity passes behind the hip and in front of the knee and ankle joints. The weight is distributed between the heel and the balls of the toes, most of it being carried by bones and ligaments, with only a minimal amount of muscle activity being required to maintain balance.

The Deep Fascia

 The deep fascia of the gluten region and thigh forms a investigating layer, the fascia lats, from which medial and later inter muscular septa divide the thigh muscles into distinct com departments. Proximal it is attached in a continuous line to the inguinal ligament, lilac crest, posterior sacrum, sacra tuberous ligament, Islamophobic rams and the body of the pubic . Three centimeters below and 1 cm lateral to the pubic tubercle an oval deficiency in the fascia, the sousaphones opening, transmits the great sousaphones vein. The fascia lam is thickened on the lateral side of the thigh, the tibial tract, which is attached distally to the lateral tibial cotyledon. Glutenous maxims and tensor fascias latte gait Impeachment to the tract. Thus they may assist in extension and mobilization of the knee. Over the political fossa the fascia is by the small sousaphones vein. The fascia a is rather like a pair of women's tights.

The ear,intracranial region and cranial nerves

The organ of hearing and balance is divided into an external ear, conveying sound waves to the tympanic membrane; a middle ear relaying the membrane's vibrations to the internal ear; and the cochlea of the internal ear, which translates these vibrations into nerve impulses. The semicircular canals, the organ of balance, are also in the inner ear. The external ear consists of the auricle (pinny) and the external acoustic meats. The auricle is formed of an irregularly shaped piece of cartilage covered by firmly adherent skin. It has a dependent globule used for earrings and an anterior Travus which projects and overlaps the opening of the menus. The external acoustic meat us (SEAM) passes almost horizontally from the Travus to the tympanic membrane in a slightly anterior direction. It is about 4 cm long. Its cartilaginous lateral third is continuous with the cartilage of the auricle; the bony medial two-thirds are formed mainly by the temporal bone. The meat us is lined by skin containing many wax secreting (coterminous) glands. It is innervated by the horticulturalist nerve anterior and the vague nerve posterior. The translucent tympanic membrane (eardrum)  separating the external and middle ears is oval in shape and lies obliquely, with its outer (lateral) surface facing down-wards and forwards. The handle of the mallets is attached to its medial surface and produces a small elevation on the drum, which can be seen with an periscope as the dumbo. 
 
 The middle car (tympanic cavity;  lies within the temporal bone. It is about 15 mm high, 15 mm long, and its medial and lateral walls curve inwards, being about 2 nun apart in their middle and 6 mm apart at the roof. The cavity, lined in part by cilia ted columnar epithelium, contains three small bones, mallets, incs and spates  the auditory vesicles. The lateral wall is formed mainly by the tympanic membrane. Above and behind the membrane is an upward extension of the cavity, the tympanic recess, which contains part of the mallets and incs. The medial wall has a central bulge, the promontory, overlying the base of the cochlea (see below). Above and behind it is the fenestration vestibule (oval window) and below it the fenestration cochleae (round window). Both these formalin lead to the inner ear. The fenestration vestibule is closed by the footplate of the states and the fenestration cochleae by a fibrous membrane. The anterior wall has two openings, the upper for tensor tympani muscle, which attaches to the handle of the mallets, the lower for the auditory (Eustachian) tube, which communicates with the pharynx. High on the posterior wall is the audits, the opening into the mastoid ant rum. Below it formalin transmit the stampedes muscle to the spates and the chords tympani. The facial nerve grooves the medial wall and then descends the medial and part of the posterior wall in a bony canal.

GASEOUS EXCHANGE IN A MAMMAL

Structure of the respiratory system

The respiratory surface of a mammal consists of many air sacs called alveolar inside a pair of lungs. The lungs are situated next to the heart in the thoracic cavity and arc connected to the atmosphere by tubes. Air passes into the lungs through these tubes. Twelve pairs of bony ribs surround and protect the lungs and heart. intercontinental muscles are attached to the ribs, and a large diaphragm separates the thorax from the abdomen.

These are involved in the ventilation mechanism, as described in section. Air enters the body through two nostrils, each of which possesses a border of large hairs which trap particles in the air and filter them out of the system. While passing through the nasal passages the air is warmed and moistened and its dour detected. Air passes from the nasal passages, through the pharynx and into the trachea. This is a tube which lies in front of the esophagus and extends into the thoracic cavity. The wall of the tube is strengthened and held open by horizontally arranged C-shaped bands of cartilage. The open section of the C is next to the esophagus. The cartilage prevents collapse of the tube during inspiration (breathing in). The cartilage can be seen in a section of the trachea. At its lower end the trachea splits into two bronchi. Within the lungs each bronchus subdivides many times into 

much smaller tubes called bronchi oles. These in turn branch into finer and finer tubes, ending with the alveolar ducts which lead into sacs called alveolar sacs. Into each alveolar sac opens a group of alveolar. A summary of these structures and their main features is provided in. The walls of most of the respiratory passage are lined with cilia ted epithelial cells and goblet cells, which secrete mucus. Mucus traps any particles, such as dust and bacteria, that have managed to pass through the hairs of the nostrils. The beating of the cilia then carries the trapped particles to the back of the buccaneer cavity where the mucus is swallowed. Note that it is not the cilia which trap the particles don't confuse them with the hairs in the nose. Mucus also moistens the incoming air. 

Flowers Fruits And Seeds

Flower  that is, those that are beautiful or fragrant, or both  have always had a strong appeal for mankind. Poets of every age have praised them. Roses, tulips, gladioli, azaleas, chrysanthemums, phlox and a host of other plants are cultivate for their showy flowers. Experts are constantly seeking to improve upon nature by making blossoms larger, more showy and more fragrant. The arrangement of flowers is an esteemed art. In the scheme of nature, however, a flower is more than an object of beauty. It is a reproductive organ, by means of which a plant carries on its kind. The most beautiful and fragrant of the flowers are concerned with this task. So are inconspicuous flowers, such as those of the ragweed, and ill smelling flowers, such as we find in the skunk cabbage and the Dutchman's pipe. The only plants whose reproductive processes are centered in flowers are the angiosperms, or flowering plants, which are the most highly evolved of all. In the flowers of angiosperms, as in the reproductive organs of the higher animals, a new organ-ism arises when an egg is fertilized by a sperm. There is an important difference, however. In the higher animals the re-productive organs produce the sex cells eggs and sperm directly. The reproductive organs of flowering plants produce spores first; then egg and sperm cells develop from the spores. The visible plant of an angiosperm  an oak tree, or a rose bush or a lilac represents the spore producing stage. The sexual stage is rep-resented only by the short span between the formation of spores and the production of sex cells by the spores shortly after their formation. Each flower originates in a bud, just as leafy  shoots do.various sequestration methods science daily. In the leafy shoot, leaves arise in the bud as minute projections at the sides of a dome shaped or slightly flattened stem tip, or growing point. In many plants the same stem tip that forms leaves changes later into a floral structure. It produces the small lateral  projections that will develop into floral organs, in much the same way that it formed the young leaves. What determines whether a plant will put forth leaves or flowers? Various factors are involved. To yield flowers there must be ample stores of food in the plant, in the form of proteins and carbohydrates. Likewise certain hormones, called florins, must be produced. Florins arise in many plants after a certain age has been reached. In such cases the plant turns to flowering after it has produced a certain number of leaves. 

                          

Heat Engines

MAN'S puny strength would never suffice to accomplish all the tasks that his fertile brain suggests. To help him perform these tasks, he has provided himself with a variety of power sources  heat, wind, water flowing downhill, electricity and, within recent years, the splitting of atoms in nuclear reactors. Heat is among the most useful of these sources of power. It drives most land vehicles (passenger automobiles, trucks, locomotives, tractors), marine craft (ocean liners, freighters, warships, motorboats) and aircraft (propelled planes, turboprops, turbojets, rockets). It serves to generate electricity in power stations and on farms. It operates blowers, pumps, certain types of fans and many other devices. In all heat engines, the chemical reaction that takes place when fuel is burned imparts a high degree of kinetic energy (energy of motion) to countless gas molecules. Generally these particles strike certain movable parts, such as pistons or the vanes of turbines, and these movable parts provide driving force. In the case of certain airplanes a forward thrust is produced as expanding gas is expelled from a nozzle set at the rear of the plane. 

An ancient Greek mathematician and physicist, Hero of Alexandria (we do not know just when he flourished), was prob-ably the first to show that heat energy could be used to perform work. He invented a steam engine called the Paleolithic , which worked on much the same principle as a modern rotary lawn sprinkler.A high return on capital tilts the kids science magazines. This engine consisted of a globe mounted between two tubes projecting upward from a steam boiler. The bent upper ends of the tubes passed through holes in the globe, which could rotate freely. Two bent nozzles were attached at opposite sides of the globe. The water in the boiler was heated the steam passed from the boiler through the upright tubes into the globe and then out through the bent nozzles attached to the globe. The reactive force of the steam issuing from the nozzles caused the globe to spin rapidly. Hero never put his Paleolithic, which was a form of steam turbine, to any practical use. 

                                        

The Planet Earth

FOUR planets in the solar system are smaller than the planet earth ; four are considerably larger. The earth, therefore, is not an outstanding member of the vast solar family. However it is the most important of all the planets to you and me, for it is our home in space  the vantage point from which we view the universe. Many theories have been proposed to explain the origin of the earth and the other planets. We have discussed some of them in other articles . They are little more than ingenious conjectures, for they are based on insufficient data. However, though we know little about the beginnings of our planet, we know a great deal about its shape, structure, properties and motions. We are quite certain that the earth is round or nearly so. Photographs of the earth taken from rockets soaring far above its surface show distinctly the curvature of our planet. Before this factual evidence became available, we could infer the roundness of the earth from certain facts. It was known, for example, that the hull of a receding ship, following the curve of the earth, disappears from view before its superstructure does. It was known also that as a total lunar eclipse develops, the earth casts a curved shadow on the moon. The earth is not a perfect sphere. Technically speaking, it is an oblate spheroid, or flattened sphere. Our planet bulges somewhat at the equator, because of its rotation. It is believed that while the earth was still in a molten state, its spin caused particles to be forced outward from the . axis of rotation. The particles were piled up least of all near the poles and most of all at the equator. Later a solid crust formed at the surface of the sphere, which had become slightly distorted. 

The diameter of the earth is 7,900 miles from pole to pole, and it is 7,927 miles in the equatorial zone. The difference between the diameters is comparatively slight, therefore  it comes to a little more than one part in 300. If the earth were represented by a globe 18 inches in diameter, the polar radius would be only 1/32 of an inch less than the equatorial radius. Someone has said that the earth is more nearly a sphere than most of the balls you would find in a bowling alley. 

The Industrial Revolution

The American Revolution has had innumerable chroniclers ; the glory and the horrors of the French Revolution are just as familiar. But the story of the Industrial Revolution, whose impact on society has become more and more pronounced as the years go by, has less often been told. The Industrial Revolution evolved through a remarkable series of inventions, going back at least as far as the middle years of the eighteenth century. Power machinery was substituted for hand tools ; the factory system first supplemented and then replaced the domestic system of work ; and industry gradually assumed the form that is familiar to us. The basic drive behind the Industrial Revolution was production. By the use of laborsaving machinery it became possible to produce far greater quantities of goods  for example, cloth  than earlier generations had deemed possible. We of the twentieth century are so much the children of the Industrial Revolution that we sometimes forget how differently men lived be-fore they learned how to harness power and set the forces of nature to do the heavy work of the world. The men who invented the machines that made the Industrial Revolution were not so much scientists as artisans carpenters, weavers, millwrights and instrument-makers, with a few mathematicians and clergymen thrown in for good measure. But the men who were chiefly responsible for carrying forward the Industrial Revolution were businessmen, capitalists and entrepreneurs (risk takers). You can compare them with the merchant adventurers of earlier centuries, who had supported scientific exploration.  From the outset these new industrialists were aware of the need for science and research in the technological development of industry. Here, for example, is part of a letter written in 1780 by Matthew Bouillon, an English manufacturer : 
                                 

 

Science in Revolution

THE last third of the eighteenth century was the period of the political upheavals that we know as the American and French revolutions. In this era there also occurred an Industrial Revolution and a Chemical Revolution, which were likewise supremely important. The Industrial Revolution involved the substitution of machinery for hand tools, the introduction of the factory system and the rise of mass production. In the course of the Chemical Revolution, old, erroneous theories were rapidly over-thrown and the science of chemistry was placed on a firm foundation. It has been pointed out that revolutions are simply signals that evolution has taken place. The forces that produce them have been gathering momentum for a long time before they break out into visible and sometimes violent changes of existing conditions. The American Revolution, which began in 1775, resulted from the gradually increasing strength of the colonies and their growing unwillingness to play a subordinate role, as well as from such specific happenings as the passing of the Stamp Act (1765), the Boston Massacre (1770) and the Boston Tea Party (1773). The age-old misery of the French peasants, popular displeasure over the privileges enjoyed by the upper classes and the spirit of defiance engendered by the French "philosophers" of the eighteenth century all these factors had molded the spirit of the French people over a period of many years, so that the actual outbreak of revolution in 1789 came merely as a long anticipated climax. 

So it was with the Chemical and Industrial revolutions. The Chemical Revolution did not spring full fledged from the brow of some scientific Zeus. It was the product of many generations of scientists and pseudo scientists, who had gruelingly accumulated facts and advanced theories. The Industrial Revolution, in its beginnings, was not so intimately bound up with the history of a science, but it was rooted partly, at least, in earlier scientific achievement.the most complex science related articles facing humanity today It waxed and grew as men realized more and more that the methods of scientific thinking could be applied to the problems of industry and could bring about astonishing improvements in the manufacture and distribution of goods. One of the important results, indeed, of the Industrial Revolution was the development of applied science, or technology. 

Acorn Worm

The acorn worms look like elongated worms with an acorn like head. The "acorn" is made up of a proboscis, or tubular structure, and a collar, into which the proboscis fits. The collar is attached to a long, flat, ruffled trunk, tapering toward the end. The animal ranges in length from an inch to four feet ; the average length is from six to ten inches. These relatively rare creatures are found on the Atlantic coast, buried in the mud and sand of the low tide zones. Like in the same way as in the vertebrates and is made up of the same tissue. Other authorities deny that the acorn worm has a chordate. They include the animal with the invertebrates, because it resembles them in many respects. The acorn worm's pharynx leads into the intestine, which is perforated with gill slits. The gills lead into a pouch, which opens to the exterior by gill pores. The intestine runs the length of the body. It ends in an anus at the tapered end of the trunk. The reproductive organs are located at the front end of the trunk. The sexes are separate; males produce sperm and females eggs. Fertilization takes place outside of the body after the sperm and eggs have been ejected from it. Some deep sea types, such as Hydrocephalus, reproduce asexually by budding. The larvae of acorn worms resemble those of the echinoderms (sea stars, sea urchins and their kin) in both structure and development. For this reason many believe that the chordates are descended from the same stock as the echinoderms. 
             

 shallow sea water one often finds orange, red or purple bearlike objects attached to rocks, piles and seaweed. These colorful "bags" are the primitive chordates In the adult animal, water bearing food particles passes through the mouth and is  filtered through gill slits. Food particles are trapped by the gill slits and enter the intestine. The water then flows into a surrounding sac  the atrium  and out through the siphon called the atrial pore. Undigested waste materials also pass out of the body by way of the atrial pore. Communicates can reproduce by budding. An adult buds again and again, producing new individuals. In time a large colony may develop on a rocky surface. Sexual reproduction also occurs. Communicates are hermaphrodites: that is, each animal produces male and female sex cells sperm and eggs. Fertilization may take place within the body ; or eggs and sperm may pass out of the body and unite elsewhere. 

Resort Climates

For a long time, many Europeans have placed much faith in the curative and restorative powers of clean air, sunshine, and pleasant weather. A 1964 report of the World Meteorological Organization in Geneva used phrases such as "climatic treatment" and "specific climatic therapy." It has been alleged that blood circulation, respiration, and skin condition are made health by exposure to favorable weather. These notions have resulted in the establishment of many health resorts in mountainous and southern-coastal areas. Baths in warm, sulfur-laden waters of certain natural springs are often part of the treatment. The benefit of the redolent waters and the air that surrounds them is debatable, but a week or two in a climatically optimal resort may send a city dweller home with a healthier mind and body. European climatologists have given a great deal of study to the most appropriate attributes of resort areas. To a certain extent, these depend on the purpose of the resort and the conditions of the people it seeks to attract. Generally, anyone seeking a pleasant period of recuperation from an illness is advised to avoid the following conditions: intense heat, particularly if accompanied by high humidity; polluted air, especially if the patient has had some kind of respiratory illness; highly changeable weather with frequent passages of fronts and cyclones; and excessively high elevations, where the presence of oxygen in the atmosphere may be too low. Sanatorium should be far enough from cities and industries to assure low concentrations of gaseous and particulate pollutants Local vegetation should be of varieties that produce little pollen. The clean, brisk air often found at moderately high elevations on the lee of a ridge or along a sea coast dominated by light sea breezes is recommended for summer resorts. On mountains or hilly terrain, spas are sometimes located in forest glades, where they are protected from strong winds by tall trees. Sunshine is considered therapeutic in many parts of the world. The World Meteorological Organization report, cited earlier, discusses the value of solar ultraviolet radiation in "hydrotherapy." These rays arc "used for their effects on skin cell metabolism, formation of substances such as vitamin I and detoxification processes." Hydrotherapy calls for long periods of exposure to the sun. Today, in the United States and a number of other countries, it is recognized that the risk of skin cancer through excessive exposure to sunlight exceeds the benefits of such exposure. In the Western Hemisphere, there is relatively little stress on health resorts, but a great many people migrate to the sunny south lands in winter. 

Comfort and Health

It is easy not to appreciate the full impact of the atmosphere on human well biophysical and psychological. Violent weather is obviously traumatic, causing injury and death to thousands every year; the effects of polluted air, though not so dramatic can still be tragic, particularly for the very young and very old with already existing lung problems. Sometimes the weather has such subtle influences that the hows and whys remain a mystery. For example, certain asthmatics find miracles in the desert air of southern Arizona while others find only disappointment, and the reasons for the differences still have not been found. It is sometimes difficult to specify in detail how the weather affects human behavior and psychological well-being, but there is no doubt that it does. Who can forget the joys of the first warm, sunny days of spring after a seemingly endless cold, gloomy winter? Also, it is well established that the strong, dry, gusty winds of the alpine foe and the California Santa Ana are associated with increases in abnormal behavior. No one needs to be told which weather conditions are physically pleasant and which ones cause discomfort. The most important element is temperature, but strong winds make cold days scent colder and hot days hotter and have many other effects as well. Even at moderate temperatures, atmospheric humanities affect human perception of air temperature. When the relative humidity is low, most people react as if the temperature were below its true value; when humidity is high, the opposite occurs. Investigations have been made of the losses and gains of heat by the human body as functions of temperature, humidity, and wind speed. Such information is particularly important in the design of clothing for use by people living and working in extreme environments . For example, the maintenance crews along the Alaskan oil pipeline must be protected from the frigid conditions that can cause frostbite or hypothermia. •

Aviation

Anyone who flies an airplane, a glider, or a balloon should take the weather into account before leaving the ground. Commercial and military pilots have ready access to the necessary information. Airplanes are designed to withstand the normal stresses imposed by violet weather events of the kind discussed in this chapter. Unfortunately there still are those rare circumstances where inclement weather, combined with pilot errors, leads to fatal accidents. The more a flier knows, through study and experience, the smaller the likelihood of such an episode. The major meteorological factors that affect an airplane in flight are wind, turbulence, lightning, hail, and aircraft icing (that is, the accumulation of ice on the leading edges of an airplane flying through a super cooled cloud). But weather considerations must begin at the runway. The length of runway needed for takeoff depends on the type and weight of the airplane, the elevation of the airport, the wind velocity, the air temperature, and the humidity. The lift imparted to an airplane's wings at any speed depends on the as density that is, the mass of air in unit volume of space which decreases with height. Departing airplanes must move faster in Denver (elevation about 5,300 feet) than in Chicago (elevation about 670 feet) to take off. To reach the higher speed, airplanes in Denver need longer runways. In addition, as the air temperature and (to a lesser extent) the humidity rise, the air density decreases; so longer takeoff runs are needed in summer than in winter. The altitude of an aircraft is usually measured by a pressure altimeter, which is calibrated according to the average pressure height relationship of the atmosphere.  Although labeled in units of altitude, the instrument actually responds to air pressure, which is a (unction of height. Since vertical distributions of temperature and density vary with time and place, so do the pressure at the ground and the rate at which pressure decreases with height. To take the deviations from average into account, a pilot adjusts the altimeter before takeoff and landing. Knowing the atmospheric pressure at the airport, the pilot sets the altimeter so that it reads the field elevation  when the airplane is on the ground. Up-to-date "altimeter settings" are normally supplied, via radio, from airport control towers. When air temperatures at flight altitudes are lower than the averages used to calibrate the altimeter, the actual altitude of the airplane is less than the one given by the altimeter; air temperatures above the averages have the opposite effect. Knowing the temperature, a pilot can easily compute a corrected altitude. Two important concerns in air travel are ceiling, which is defined as the height of the base of the lowest layer of clouds or other obscuring phenomenon that hides more than half the sky, and visibility, the greatest distance at which one can see and identify prominent objects. Low ceilings and visibility most often result from fogs or stratus clouds, but heavy snow or rain, blowing sand, or dense smoke and haze can also be causes. These conditions arc most significant during landings and takeoffs. In very dense fogs, ceilings and visibility can be nearly zero, bringing traffic to a halt. Fortunately, these "zero zero" conditions are not common. More often, ceilings are reduced to a few hundred feet and visibility to less than a mile, in which cases air traffic continues, though at a slower rate, in and out of airports having suitable radio or radar systems that can guide an airplane to a safe touchdown. Some types of fogs and low cloud layers form or become more dense on clear nights as a result of cooling by thermal radiation to the night sky. For this reason, ceilings and visibility may drop during the night and early morning. Pilots of small airplanes, who are often required to fly with the ground in sight, should schedule flights out of fog-prone airports for periods after the sun has burned off the fog and before fog begins to form in the evening or night.

Water And Vapor

Quite clearly, the results of farming depend on adequate and timely sup-plies of water. The critical factor is not rainfall but soil moisture throughout the life history of the crop involved. As everyone with house plants or a garden knows, the appropriate conditions depend on the plant species, the stage of growth, the properties of the soil, and air temperature and humidity. Water in the soil feeds and cools growing vegetation as it passes into the plant through the root systems. The flow of fluid transports nutrients into the stems and leaves. When the air is hot and dry, the tomatoes of the leaves open and a great deal of water vapor transpires into the air. In the process, the plant is cooled. In a sense, this is the vegetative equivalent to human perspiration. Because of uncertainties about the quantity and scheduling of watering needed to achieve optimum crop yields, irrigation practices have been less than maximally efficient. Vegetation can survive and even thrive in moderately dry soil, but when there is inadequate water, leaves begin to wilt. A heavy rainfall or deep irrigation will improve the health of the plants, but will not entirely undo the harm caused by the desiccation. This means, of course, that when irrigation is available, a grower should not wait for signs of distress; that is, the plant should not be used as a measure of water insufficiency. The crucial factor, soil moisture, should be monitored directly. A procedure widely recommended to the home gardener is poking a metal rod or digging a few inches into the soil to see if it is wet. Water should be applied when the soil is dry. Surprisingly, in arid regions, where irrigation is a necessary practice, ,a great many plants are killed by over-watering. This happens when an amateur farmer, seeing dry surfaces, incorrectly assumes that the dryness extends into the root zone. 

Commercial farmers sometimes use soil augers to gags the state of the soil. Another approach is to install electronic moisture sensors whose out-puts are recorded continuously. Some authorities believe these procedures are inadequate because they do not measure the wetness at enough points through a deep layer of earth. An alternative approach to the monitoring of soil moisture is to maintain a water budget of the cultivated field. This involves measuring the water added by precipitation and irrigation and balancing it against the water leaving the field by evaporation and transpiration. This requires computation of the last two processes, which are often lumped together and called transpiration. 

the growth of a thunderstorm

the growth of a thunderstorm is impeded by a stable layer sometimes a temperature inversion—that serves as a lid over the cloud top. Asia thunderstorm matures, a draftsman develops adjacent to the updraft core. Both drafts arc composed of churning high-speed air resembling a tumbling stream of rushing water. This pattern of air motion accounts for the turbulence: experienced by an airplane flying through a thunderstorm. The drafts may carry an airplane up or down while eddies in air velocity buffet it and, in extreme cases, muse structural damage. Most thunderstorms pass through their lifetimes in less than an hour, yielding a few lightning strokes and rain. Provided no one is struck by lightning, these storms do a great deal more good than harm. The rain is usually very beneficial, particularly to farms. The cool air that precedes an arriving thunderstorm on a hot summer day is the result of air from high altitudes being cooled by the evaporation of water drops; the air descends to the ground and spreads out, mostly in the direction of the storm motion. Some thunderstorms, because of their large sizes and long duration, arc called "supermodel" thunderstorms. They can last for many hours and have strung, persistent updrafts and downdrafts. They commonly occur as parts of a squall line, a line of thunderstorms, often oriented northeast-southwest, that sweeps across the Great Plains ahead of an advancing cold front. Super cell storms an produce violent weather. They are the sources of tornadoes and hail. As these storms move over the flatland of Kansas, Nebraska, Iowa, Illinois, and surrounding states, they sometimes lay down swaths of hail that devastate wheat, corn, and soybeans (Figure 3-16). In an average year, hail damage to agriculture in the United States amounts to more than 5700 million. Hailstorms also cause widespread damage in many other parts of the world: the fruit orchards of northern Italy, the grapevines of the Caucasus region of the Soviet Union, the tea plantations in Kenya, the farmlands of South Africa and Argentina. In India, 246 people were killed during a severe hailstorm near New Delhi in April 1888.

                                           

The Atmosphere and the Weather

storms accompanying low pressure centers associated with fronts are some-times called "frontal cyclones." References to cyclones are often misunderstood; they usually evoke thoughts of violent weather. There is some justification for such a reaction: Over the central United States, tornadoes are commonly called cyclones; in Southeast Asia, Australia, and Mexico, the name is applied to the intense tropical storms known as hurricanes in the United States. These are not improper uses of the name, although most cyclones over the earth are centers of low pressure that do not contain threatening weather. The middle latitudes of the earth experience, at regular intervals, the passage of cyclones with their associated clouds and precipitation. On weather satellite photographs, cyclones sometimes have very distinctive patterns (Figure 3-7). Some places see more of them than others do because there are favored regions for the formation of cyclones. Cyclones most often develop along well-established, nearly stationary fronts. In winter, cold air from the Arctic commonly sweeps southward.

                                         

over North America behind a cold front, pushing warm air ahead of it. Usually the Rocky Mountains act as a barrier that stops the air from moving westward. As a result, the front separating the polar air over the Great Plains from warmer air becomes stationary along the eastern foothills of the Rocky Mountains. Many cyclones develop along this front, particularly over Colorado (Figure 3-8). On a weather map, a new cyclone first appears on the front as a wavelike wiggle that coincides with an area of falling atmospheric pressure. In some cases, the wave amplitude increases and pressure continues to decrease. Clouds appear, which thicken, become widespread, and even-tually yield rain or snow. As all this is going on, the cyclone usually moves more or less eastward under the influence of the major west wind currents dominating the middle latitudes. In winter, polar air often pushes southward until the front becomes stationary in the form of a giant arc along the Gulf coast and up the eastern seaboard. Cyclones frequently develop along this front and move north-ward or northeastward. Many of them originate over the Gulf. Another favorite spawning ground is just off Cape Hatteras, North Carolina. 

Carbon Trading

Enthusiasm is spreading for cap and trade systems to regulate the amount of carbon dioxide (CO₂) emitted to Earth's atmosphere. In 1990, the U.S. Environmental Protection Agency set a limit on sulfur dioxide (SO₂) emissions from obvious point sources and allowed those who emit less than their quota to trade excess allowances. As a result, regional acid deposition was dramatically reduced. Can the world do the same for CO₂ ? Fundamental differences in the bio geochemistry of SO₂ and CO₂ suggest that establishing a comprehensive, market-based cap and trade system for CO₂ will be difficult. For SO₂, anthropocentric point sources (largely coal-fired power plants), which are relatively easy to control, dominate emissions to the atmosphere.

Natural' sources, such as volcanic emanations, are comparatively small, so reductions of the anthropocentric component can potentially have a great impact, and chemical reactions ensure a short lifetime of CO₂ in the atmosphere.CO₂ , in contrast, comes from many distributed sources, some sensitive to climate, others sensitive to human disturbance such as cutting forests. It is thus impossible to control all of the potential sources. combustion are one of the smaller components of the atmospheric flux of CO₂. which is dome• noted by exchange between forests and the oceans. During most of the past so,000 years, the uptake and loss of CO₂ from forests and the oceans must have been closely balanced, because atmospheric CO₂  showed' little variation until the start of the Industrial Revolution. CO, from coal, oil, and natural gas combustion now comics from many segments of society. including electric power generation, industry, home heating, and transportation. Unbalanced by equivalent anthropological sinks for carbon, fossil fuel emissions account for the vast majority of the rise of CO₂ in Earth's atmosphere. Caps on emissions, like those instituted for SO₂ ,will be difficult to institute if the burden of reducing CO₂  is to be borne equally by all emitters. Because land plants take up CO₂  in photo syn• thesis and store the carbon in biomass, forests and soils seem to be attractive venues to store CO₂ . Market•based schemes propose substantial payments and credits to those who achieve net carbon storage in forestry and agriculture, but these projected gains are often small and dispersed over large areas. Carbon Trading news in freshsciencenews
 We will need to net any such carbon uptake against what might have occurred without climate-policy intervention. Conversely, will Canada and Russia be billed for incremental CO₂  releases that stem from the warming of cold northern soils as a result of global warming from the use of fossil fuels worldwide? If credit is given to those who choose not to cut existing forests, the increasing total demand for forest products will shift deforestation to other areas.

Carbon Trading Over Taxes

As the United States moves inevitably toward climate legislation, discussion has shifted from the science to the policy options for slowing emissions of carbon dioxide CO₂ and other greenhouse gases. Some favor a tax on CO₂ emissions—referred to as a C tax (r). Others favor government subsidies (2). If high enough to alter consumer behavior, a carbon tax would reduce emissions by raising the effective price of carbon-intensive energy relative to carbon-free sources. Subsidies may speed development of specific, targeted low-C technologies. But a market-based system with an economy wide cap on emissions and trading of emission allowances would do the same, while having distinct advantages 0). Most important, a cap and trade system, coupled with adequate enforcement, would assure that environmental goals actually would be achieved by a certain date. Given the potential for escalating damages and the urgent need to meet specific emission targets (4), such certainty is a major advantage. A federal cap and trade system could be incorporated into existing emissions-trading frame-works and markets, such as the Kyoto Protocol's international market or sub rational ones like the Regional Greenhouse Gas Initiative. Earth's climate is agnostic about the location and type of CO₂ emissions and is sensitive only to the total burden of CO₂ It makes sense, therefore, to design a climate policy that taps all possible avenues to limit net  CO₂ emissions. Trading of emissions Science news articles across all sectors of the economy addresses this by allowing emitters to purchase carbon offsets from businesses that are able to lower their own emissions below their allocation. If trading were incorporated into an international system, U.S. firms and consumers could meet emissions targets at reduced costs by substituting less expensive cuts in, for example, developing countries, for expensive emissions cuts in the United States. Because investment would be funneled to technologies that reduce CO₂ emissions at the least ant, the overall expense of the program would be minimized. Cutting emissions of pollutants is admittedly notes  complicate crosscutting      CO₂        emissions, and transaction costs can be a factor. Nevertheless, the United States was able to reduce sulfur oxide emissions ahead of schedule and at 30% of the projected cost using a market-based cap and trade system (5). Elimination of lead from gasp. line and phaseout of ozone-depleting chemicals were also facilitated by emissions-trading programs. 

A Guide to Sequestration

Climate change concerns may soon force drastic reductions in carbon dioxide CO₂ emissions. In response to this challenge, it may prove necessary to render fossil fuels environmentally acceptable by capturing and sequestering CO₂  until other inexpensive, dean, and plentiful technologies are available. Today's fossil fuel resources exceed 5000 megatons of carbon (GT C) (I), compared with world consumption of 6 Gt C /year, assuring ample transition time. However, by 2050, the goal of stabilizing the atmospheric CO₂   con, cent ration while maintaining healthy economic growth may require "carbon-neutral" energy in excess of today's total energy consumption (2). Lowering world CO₂ emissions to 2 GT C/year 

 Estimated storage capacities and times for various sequestration methods science daily. The "fossil carbon" range includes at its upper end methane hydrates from the ocean floor. The "oxygen limit" is the amount of fossil carbon that would use up all oxygen available in air for its combustion. Carbon consumption for the zits century ranges from 600 Gt (current consumption held con-stent) to 2400 Gt. "Ocean acidic" and "ocean neutral" are the ocean's uptake capacities for carbonize acid and neutralized carbonize acid, respectively. The upper limits of capacity or lifetime for underground injection and mineral carbonates are not well constrained. 

Preparing to Capture Carbon

Carbon sequestration from large sources of fossil fuel combustion, particularly coal, is an essential component of any serious plan to avoid catastrophic impacts of human-induced climate change. Scientific and economic challenges still exist, but none are serious enough to suggest that carbon capture and storage will not work at the scale required to offset trillions of tons of carbon dioxide (COR) emissions over the next century. The challenge is whether the technology will be ready when society decides that it is time to get going. Strategies to lower CO2 emissions to mitigate climate change come in three flavors: reducing the amount of energy the world uses, either through more efficient technology or through changes in lifestyles and behaviors; expanding the use of energy sources that do not add to the atmosphere; and capturing the CO2 from places where we do use fossil fuels and then storing it in geologic repositories, a process known as carbon sequestration. A survey of energy options makes clear that none of these is a silver bullet. The world's energy system is too immense, the thirst for more and more energy around the world too deep, and our dependence on fossil fuels too strong. All three strategies are essential, but the one we are furthest from realizing is carbon sequestration. The crucial need for carbon sequestration can be explained with one word: coal. Coal produces the most CO2 per unit energy of all fossil fuels, nearly twice as much as natural gas. And unlike petroleum and natural gas, which are predicted to decline in total production well before the middle of the century, there is enough coal to last for centuries, at least at current rates of use, and that makes it cheap relative to almost every other source of energy (Table r). Today, coal and petroleum each account for roughly 40% of global CO2 emissions. But by the end of the century, coal could account for more than 80%. Even with huge improvements in efficiency and phenomenal rates of growth in nuclear, solar, wind, and biomass energy sources, the world will still rely heavily on coal, especially the five countries that hold 75% of world reserves (see (6)): the United States, Russia, China, India, and Australia (1). As a technological strategy, carbon sequestration need not apply only to coal plants; indeed, any point source of CO2 can be sequestered, including biomass combustion, which would result in negative emissions. latest tech fresh news Carbon sequestration uptake through reforestation or fertilization of marine photo plankton. But the potential to enhance bio-logical uptake of carbon pales in comparison to coal emissions, ever more so as India, China, and the United States expand their stock of coal-fired power plants. So developing and deploying the technologies to use coal without releasing CO2 to the atmosphere may well be the most critical challenge we face, at least for the next too years, until the possibility of an affordable and completely non—fossil energy system can be realized. 

Critical Assumptions in the stern

 In November 2006, the British government presented a comprehensive study on the economics of climate change , the Stem Review. It painted a dark picture for the globe: 'III we don't act, the overall costs and risks of climate change will be equivalent to losing at least 5% of global GDP [gross domestic product] each year, now and forever. If a wider range of risks and impacts is taken into account, the estimates of damage could rise to 20% of GDP or more." The Stem Review recommended urgent, immediate, and sharp reductions in greenhouse-gas emissions. These findings differ markedly from economic models that calculate least cost emissions paths to stabilize concentrations or paths that balance the costs and benefits of emissions reductions. Mainstream economic models definitely find it economically beneficial to take steps today to slow warming, but efficient policies generally involve modest rates of emissions reductions in the near term, followed by sharp reductions in the medium and long term (2-5). A standard way of showing the stringency of policies is to calculate the ''carbon tax," or penalty on carbon emissions. A recent study by the author estimates an optimal carbon tax for ions of about $30 per ton carbon in today's prices, rising to $85 by the mid-21st century and further increasing after that (5). A similar carbon price has been found in studies that estimate the least-cost path to stabilize carbon dioxide concentrations at two times protein dust rial levels (2). The sharply rising carbon tax reflects initially low, but rising, emissions reduction rates. We call this the climate-policy ramp, in which policies to slow global warming increasingly tighten or ramp up over time. A $30 carbon

 Comparing the optimal carbon tax under alternative discounting assumptions. Integrated model of clinical trials news. Climate and the Economy (DICE model) (5) integrates the economic cods and benefits of greenhouse gases (Gig) reductions with a simple dynamo representation of the scientific and economic links of output, emissions, concentrations, and clip' mate change. The DICE model is designed to choose levels of investment in tangible capital and in Gallic re:Inchon% that maximize economic welfare. It calculates the optimal carbon tax as the price of carbon emissions that will balance the incremental of abating carbon emissions with the incremental benefits of lower future damages from climate change. Using the DICE model to optimize climate policy leads to an optimal carbon tax in boos of around Ssh per ton carbon (shown here as 'DICE baseline). If we substitute the Stern Review-s assumptions about tune astounding and the consumption elasticity into the DICE model, the calculated optimal carbon tax is much higher and rises much more rapidly (shown as 'Stern assumption:). tat may- appear to he a modest target. but it is at least to times the current globally averaged carbon tar implicit in the Kyoto Protocol (shown as Stern assumptions). What in the logic of the ramp? In a world when- capital la productive and damages are far in the fun in (see chart affirm). the highest. return investments today are primarily in Ian. gable, nontechnical. and human capital. In the inning decade.. damages are predicted to rise relative to output. As that occurs. rt becomes efficient to shift investment toward more intensive emissions reductions and the IRK COM paying higher carbon taxes. The exact time  of emissions reductions depends on details of emit. damages, learning, and the extent In which climate change and damages are nonlinear and semitrailer. The Stern Review proposes to rime Ill to inn table for emissions reductions slur . forward. It suggests global emulsions reductions of between yo% and 70%  the neat two decades. °bin-Me consistent with a carbon tat of about  per ton today. or about to times the level mg. Rested by standard economic models. Green that the Stern Review embraces . traditional economic techniques such as those described in it-t). how does 0 get such differ.  results and strangles, Flaying analyzed the Stern Review in (6) 'which also contains a list of recent analyses). I find that the difference sterns ah nowt emirs-Is-from Its technique for cal. cabling disgusting rates and only marginally on new science or economics. The reasoning has questionable foundations in terms of its ethical assumptions and also leads to economic results that are inconsistent with market data. Some background on growth economics and discounting concepts I. necessary to under-stand the debate. monogramming alternative trajectories for emissions reductions. the key  variable is the real return on capital. which measures the net yield on investments in capital. education. and technology. In principle. this is observable in the marketplace. For rumple. the real pretax return on U.S. snipe rate capital over the last four decades has aver-aged about 0.07 per year. Estimated real returns on human capital range from 0.06 to > 0.20 per year, depending on the country and time period (7). The return on capital is the "discount rate" that enters into the determination of the efficient balance between the cost of emissions reductions today and the benefit of reduced climate damages in the future. A high return on capital tilts the kids science magazines balance toward emissions reductions in the future, whereas a low return tilts reductions toward the present. The Stern Review's economic analysis recommended immediate emissions reductions because its assumptions led to very low assumed real returns on capital. Where does the return on capital come from? The Stern Review and other analyses of climate economics base the analysis of real returns on the optimal economic growth theory (8, 9). In this framework, the real return on capital is an economic variable that is determined by two normative parameters. The first parameter is the time discount rate, denoted by p, which refers to the discount on future utility or wel-fare (not on future goods, like the return on capital). It measures the relative importance in societal decisions of the welfare of future generations relative to that of the current generation. A zero discount rate means that all generations into the indefinite future are treated the same; a positive discount rate means that the welfare of future generations is reduced or "discounted" compared with nearer generations. Analyses are sometimes divided between the ''descriptive approach," in which assumed discount rates should conform to actual political and economic decisions and prices, and the "prescriptive approach," where discount rates should conform to an ethical ideal, sometimes taken to be very low or even zero. Philosophers and economists have conducted vigorous debates about how to apply discount rates in areas as diverse as economic growth, climate change, energy, nuclear waste, major infrastructure programs, hurricane levees, and reparations for slavery. The Stern Review takes the prescriptive approach in the extreme, arguing that it is indefensible to make long-term decisions with a positive time discount rate. The actual time discount rate used in the Stern Review is 00.01 per year, which is vaguely justified by estimates of the probability of the extinction of the human race. 

Sea Level Rice

A semi-empirical relation is presented that connects global sea level rise Tc global mean surface temperature. It is proposed that, for time scales relevant to anthropocentric warming, the rate of sea level rise is roughly proportional to the magnitude of warming above the temperatures before the Industrial Age. This holds to good approximation for temperature and sea level changes during the both century, with a proportionality constant of 3.4 mm/year per °C. When applied to future warming scenarios of the Intergovernmental Panel on Climate Change (IPECAC), this relation-ship results in a projected sea level rise in 2100 of o.5 to 1.4 m above the 1990 level. Understanding global sea level changes is a difficult physical problem, because complex mechanisms with different time scales play a role Oh including thermal expansion of water due to the uptake and penetration of heat into the oceans, input of water into the ocean from glaciers and ice sheets, and changed water storage on land. Ice sheets have the largest potential effect, because their complete melting would result in a global sea level rise of about 70 m. Yet their dynamics are poorly understood, and the key processes that control the response of ice flow to a warming climate are not included in current ice sheet models [for example, melt water lubrication of the ice sheet bed (2) c increased ice-stream flow after the removal c buttressing ice shelves (3)]. Large uncertainties exist even in the projection of thermal expand Sion, and estimates of the total volume of ice it] mountain glaciers and ice caps that are remote from the continental ice sheets are uncertain by a factor of two (4). Finally, there are as yet NC published physically based projections of ice Los* from glaciers and ice caps fringing Green lark and Antarctica. For this reason, our capability for calculating future sea level changes in response to a given surface warming scenario with present physics based models is very limited, and models are not able to fully reproduce the sea level rise of recent decades.  climate of current events earth science and ice sheet models are generally lower than observed rates. Since 1990, observed sea level has followed the uppermost uncertainty limit of the IPECAC Third Assessment Report (Algal), which was constructed by assuming the highest emission scenario combined with the highest climate sensitivity and adding an ad hock amount of sea level rise for Mice sheet uncertainty" (1). While process-based physical models of sea level rise are not yet mature, semi-empirical

Prioritizing Climate Chance

Investments aimed at improving agricultural adaptation to climate change inevitably favor some crops and regions over others. An analysis of climate risks for crops in 12 food-Secure regions was conducted to identify adaptation priorities, based on statistical crop models and climate projections for 2030 from 20 general circulation models (Gyms). Results indicate South Asia and Southern Africa as two regions that, without sufficient adaptation measures, will likely suffer negative impacts on several crops that are important to large food-insecure human populations. We also find that uncertainties vary widely by crop, and therefore priorities will depend on the risk attitudes of investment institutions. Adaptation is a key factor that will shape the future severity of climate change impacts on food production (2). Although relatively inexpensive changes, such as shifting planting dates or switching to an existing crop variety, may moderate negative impacts, the biggest benefits will likely result from more costly measures, including the development of new crop varieties and expansion of irrigation (2). These adaptations will require substantial invest-mints by farmers, governments, scientists, and development organizations, all of whom face many other demands on their resources. Prioritization of investment needs, such as through the identification of "climate risk hot spots" Oh is therefore a critical issue but has received limited attention to date.components to science magazines for kids be essential to any prioritization approach: (i) selection of a time scale over which impacts are most relevant to investment decisions, (ii) a clear definition of criteria used for prioritization, and (iii) an ability to evaluate these criteria across a suite of crops and regions. Here, we focus on food security impacts by 2nd—a time period most relevant to large agricultural investments, which typically take 15 to 30 years to realize full returns (4, 5). We consider several different criteria for this time scale. First is the importance of the crop to a region's food-insecure human population [hunger importance (HI)]. Second is the median projected impact of climate change on a crop's production by 2030 (indicated by CO), assuming no adaptation. For this analysis, we generate multiple (i.e., IMO) projections of impacts based on different models of climate change and crop response; in order to capture relevant uncertainties. The projections are then ranked, and the average of the 5th and 51st values are used as the median. A third criterion is the fifth percentile of projected impacts by 2030 (where Com indicates the fifth value of the ranked projections), which we use to represent the lower tail, or "worst case," among the projections. Finally, we consider the 95th percentile of projected impacts by 2030 (where C indicates the 95th value of the ranked projections), which we use to represent the upper tail, or "best case," among the projections. We first identified 12 major food-insecure regions. each of which (i) comprise groups of countries with broadly similar diets and agricultural production systems and (ii) contain a notable share of the world's malnourished individuals as estimated by the Food and Agriculture Organization (MO) (Table r; see fig. Si online for details on regions). For each region, we computed the HI value for each crop by multiplying the number of malnourished individuals by the crop's percent contribution to average per-capital calorie consumption [see supporting online material (SOME) Text Si and table Si J. A hunger importance ranking (HIRE) was then generated by ranking the HI values for all crop-by-region combinations. Rice. maize, and wheat contribute roughly half of the coal-rise currently consumed by the world's poor and

Michael Oppenheimer

We disagree with Solomon eta . that our Policy Forum was misleading. We correctly noted that model-based numerical ranges for century sea level rise presented in the Working Group I (WIG) "Summary for Policymakers" (SPAM) (Table SPAM-3) did not account for the uncertainty resulting from potential increases in the rapid dynamic response of ice sheets. Solomon a AL. challenge this assertion by pointing instead to qualitative statements in the SPAM, implying that the latter provide a satisfactory accounting of uncertainty. But the distinction between numerical values highlighted in a prominent table and narrative qualifications of such numbers is critically important. Numbers are powerful, grabbing the readers' attention, whereas qualifications are often ignored. For example, the tabular values, indicating a maximum sea level rise of 59 cm during the 21st century, are cited frequently in the public discussion absent any qualification. We did not imply, as Solomon ET AL. argue, that the WEI SPAM omitted information from paleolithic studies in evaluating uncertainty in sea level rise beyond the 21st century. We suggested that it gave too much credence to ice sheet health articles models compared  For example, in reporting only a model-based estimate for the time scale of a long-term contribution (from Greenland), the WIG SPAM gives short shrift to the implications of observations of fast responses in the ice sheets in both Greenland and western Antarctica, narrative qualifications to the contrary notwithstanding. Such an approach understates the range of opinion in the relevant expert community on the potential magnitude and rate of the ice sheet contribution as indicated by studies reviewed during the Fourth Assessment Report (ARE) (i). Further perspective on this question is provided by the ARE Synthesis Report (2). Finally. contrary to Solomon ct Al.'s assertion, our suggestions for improving the treatment of uncertainty were made specifically with the shortcomings of ice sheet modeling in mind. It makes little sense to highlight model-based projections of sea level rise when models that are supposed to account for the ice sheet component have failed the test against reality. Other approaches provide important additional perspectives. For example, the fact that two independent semi-empirical analyses estimating uncertainties in future sea level rise have been published recently (3, 4) suggests that observation-based methods yield important insights where models are deficient. We do not propose that IPECAC conduct new research: Rather, we argue that it take full advantage of what has already been produced. IPECAC also has the flexibility to fill gaps in modeling and analysis where the completeness of assessment calls for it, and it has done so many times. In anticipation of a Fifth Assessment. and realizing that ice sheet models may not improve rapidly, IPECAC should encourage the development of more comprehensive approach to uncertainty. As it has done for other arenas, such as emissions scenarios or abrupt climate change, I P CC could spur research into empirical approaches, formalized expert elicitation, and comprehensive analysis of Paleocene extent and sea level, each carried out with a specific view toward informing quantitative judgments on the range of future sea level. Holding work-shops on this problem over the next few years would fit neatly into IPECAC tradition. Three of us are authors of ARE, well aware of the difficulty of assessment. A premise of our Policy Forum is that I P CC has done a superb job of establishing the scientific consensus. But in a high-stakes problem like global warming. governments need to calibrate policy to the full range of plausible outcomes, for sea level rise and for all other key uncertainties.

A Closer Look at the Ipcc Report

In the future, Arctic warming and the melting of polar glaciers will be considerable, but the magnitude of both is uncertain. We used a global climate model, a dynamic ice sheet model, and paleolithic data to evaluate Northern Hemisphere high-latitude warming and its impact on Arctic ice fields during the Last Inter glaciation. Our simulated climate matches paleolithic observations of past warming, and the combination of physically based climate and ice sheet modeling with ice core constraints indicate that the Greenland Ice Sheet (GUYS) and other circumstantial ice fields likely contributed 2.2 to 3.4 m of sea level rise during the Last Interrelation. 

Determining the sensitivity of the Arctic climate system to anomalous forcing and understanding how well climate models can simulate the future state of the Arctic are critical priorities. Over the past 3 years, Arctic surface temperatures have increased o.3°C per decade (0); September Arctic sea-ice extent has decreased 7.7% per decade (2); and the seasonal ablation area for Greenland has increased, on average, by 16% (3-3). The global climate models being used to estimate future scenarios of Arctic warmth give polar warming of o.7°C to 4.4°Ca large ranges well as a reduction of Arctic sea ice of up to 65% at the time of the doubling of atmospheric CO (6). The Last Inter glaciation (LUG, about 130,000 to 116,000 years ago) is the last time that the Arctic experienced summer temperatures markedly warmer than those in the 20th century and the late Holocene, and it also featured a significantly reduced GUYS. Climate models need to be able to current event science articles. reproduce this large. warm climate change in the Arctic if they are to lie trusted in their representation of Arctic processes and their prediction for the future. Prerecords indicate much warmer Arctic summers during the LUG. Storm beaches and ancient barrier islands with mollusks of LUG age indicate that the open water north of Alaska was more extensive and Listed seasonally longer (7) Arboreal forest communities expanded pollard by as much as boo to moo km in Russia (8). reaching the coast everywhere crept in Alaska (9) and central Canada. Total gas evidence from L ice in the Greenland Ice Core Proctor (GRIP) ice (Orr indicates that the Summit region remained ice centered. although possibly up to about Soto m lower than the we level at per', rm. at sonic tune m the LING (soy In contrast. basal ice at Dye-3 (southern Greenland); in the Agassi Demon. and Meighen ice caps in the Canadian Arctic; and possibly in Camp Century (northwest Greenland) suggest that these doll sites were Refine during the LING (so. 1). The increased presence of vegetation over southern Greenland is reconstructed from plant macro. fossils 07) and fern spores (0). Elsewhere. pol• lens. Insects. marine plankton. and other pros ices document the magnitude of LUG summer warmth across the Arctic (14). We conducted climate simulations for the LUG with a global coupled ocean-atmosphere-land sea ice general circulation model National Center for Atmospheric Research (N CAR) Community Climate System Model (COSMIC) Dem. We also used we sheet simulations with a three-dimensional. coupled kindhearted-flow model 06). which spans the entire western